integrated general · pdf filechemical reactions involve the movement and the changes in the...

Integrated General Biology A Contextualized Approach

Active Learning Activities

Student Version FIRST EDITION

Jason E. Banks

Julianna L. Johns

Diane K. Vorbroker, PhD

Molecules, Compounds, & Chemical Bonds Active Learning Activities

Let's Bond, Chemically 2

Chapter 3 Molecules, Compounds, & Chemical Bonds

Section 3.1 Let's Bond, Chemically Directions for the Student:

This lesson is designed for you to complete, on your own or in your study group. Use your notes and follow along in the text, as you find necessary.

Objectives: 1. Define a chemical bond. 2. Describe trends in the chemical behavior of metals and non-metals. 3. Describe ionic bonds and predict the chemical formula for ionic bonds. 4. Differentiate between a cation and an anion. 5. Identify groups of atoms as a compound and/or a molecule.

Chemical reactions involve the movement and the changes in the arrangement of the electrons. While

the nucleus of the atom must also be understood, we will be focusing on the electrons and their

positions. Therefore, instead of drawing each nucleon, only the chemical symbol for the atom or ion

will be drawn to represent the nucleus. Sometimes all of the electrons will be drawn, and sometimes

only the valence electrons will be drawn. You must be comfortable with all of the different notations

and be able to move freely between them.

1. Look at the diagram of sodium and chlorine. Remembering that the most stable arrangement of electrons is a complete outermost shell, predict what will happen when a sodium atom meets a chlorine atom.

Sodium has one electron in its outer shell. Chlorine has seven electrons in its outer shell. When they react sodium loses an electron to become a sodium ion with a charge of +1. Chlorine atoms accept an electron to become chloride ions with a charge of -1. After reacting the sodium and chloride ions have a full outer shell of electrons. A full outer shell of electrons is a stable arrangement.

Sodium and chlorine bond together to form table salt. There are many other salts, but sodium chloride is

the most famous (notice that we change the ending on the non-metal to “-ide” when it forms an ion).

If sodium loses its outermost electron, its new outermost shell will be complete (the 2nd orbital). And, if

chlorine gains the electron from sodium, chlorine will also have a complete outermost shell with 8

electrons in its 3rd orbital.

2. What type of element (metal, nonmetal or metalloid) is Sodium? metal

3. What type of element (metal, nonmetal or metalloid) is Chlorine? nonmetal



Atoms can be seen as the building blocks for life. Atoms link together to form larger molecules and build

the structures that make up everything we can see, touch, taste or smell. But what happens when atoms

bond together?

There are many different types of bonds, but we will focus here on ionic bonds.

As the name implies, ions are formed when two atoms form an ionic bond.

4. What are the two different types of ions? Use the examples from the first question.

An ion is an atom or group of atoms in which the number of electrons is not equal to the number of protons, giving it a net positive or negative electrical charge. An anion is an ion that is negatively charged, and is attracted to the anode (positive electrode) in electrolysis. A cation has a net positive charge, and is attracted to the cathode (negative electrode) during electrolysis. In the first question, Na is considered to be the cation as it loses an electron and its overall charge becomes positive. Therefore, Cl is considered to be the anion because it gains an electron and its overall charge becomes negative.

Some atoms lose electrons and some atoms gain electrons to form a complete outermost shell (valence

orbital). Metals tend to lose electrons and nonmetals tend to gain electrons. This means that metals and

nonmetals will form ionic bonds when they meet. In ionic bonds, the electron is transferred from the

metal to the nonmetal. This means that the electron is no longer counted for the metal, and is now part

of the nonmetal. Now that a charged particle has been transferred, the charge on the atom has now

changed, and it is now a charged atom, or ion. This ion now has a complete outermost shell, and is an

example of the Octet Rule (or Duet rule if there is only one orbital).

5. The chemical symbol for magnesium is drawn (as the nucleus). Using question number 1 as a guide, add all of magnesium’s electrons (in its atomic state, not its ionic state). Use the periodic table to help you remember how many electrons can fit into each orbital (by counting the number of spaces in each row until you get to the element you are drawing).

Mg



6. Draw sulfur (with its chemical symbol as the nucleus) and all of its electrons in the atomic state.

7. Complete the table.

8. Draw the electron dot diagram for each element from the table. Then draw an arrow from the

metal’s electron(s) to the nonmetal’s open space(s) representing a transfer of the electron(s) and

the formation of ions. Name the newly formed compound with the metal first and the nonmetal

second, and change the ending of the nonmetal to “-ide”. Also, give the chemical formula for the

compound (count how many of each element there are and write it as a subscript, even if it is a “1”

for now).

Name Formula Diagram

Sodium Chloride Na1Cl1

Element Type # of

Protons

# of Valence

Electrons How it forms an

Ion

New # of Electrons (total) as

an ion Ionic Charge (p

– e)

Sodium metal 11 1 Loses 1 electron 10 11 – 10 = 1+

Chlorine nonmetal 17 7 Gains 1 electron 18 17 – 18 = 1-

Magnesium metal 12 2 Loses 2 electrons 10 12 – 10 = 2+

Sulfur nonmetal 16 6 Gains 2 electrons 18 16 – 18 = 2-

Aluminum metal 13 3 Loses 3 electrons 10 13 – 10 = 3+

Nitrogen nonmetal 7 5 Gains 3 electrons 10 7 – 10 = 3-



Magnesium Sulfide Mg1S1

Aluminum Nitride Al1N1

Notice how each of the parts of problem number 7 are perfectly matched . . . sodium needed to lose

one electron while chlorine need to gain one electron, and magnesium needed to lose two electrons

while sulfur needed to gain two electrons, and so on.

Since these particular elements are matched so well, only one atom of each element was required to

form a complete valence shell. This is not always the case, and additional atoms of either element may

need to be added to form a stable compound (group of at least two different elements bonded

together, like when sodium and chlorine bond together).

9. Draw the electron dot diagrams for the elements and add additional atoms as necessary to empty

the valence shell of the metal and complete the valence shell of the nonmetal. Draw arrows showing

where the electrons will go. Then name the compound you formed.


Magnesium Chloride

Mg1Cl2



Aluminum Bromide

Al1Br3

Sodium Oxide

Na2O

Sodium Phosphide

Na3P

Adding more atoms of the same elements makes sense because they are already there in the reaction—

we just haven’t drawn all of them. Think of it this way: it would be extremely difficult to get only two

atoms together, but almost anyone could add many magnesium atoms to many chlorine atoms. There

are extra magnesium and chlorine atoms all around the two that happened to be drawn.

In some cases, it may be necessary to add more atoms of both elements. Every electron from the metal

must be moved and every space in the valence shell of the nonmetal must be filled.

10. Draw the electron dot diagrams for the following elements. Add more atoms of each element as

necessary. Name the ionic compound and give its chemical formula.




Magnesium Nitride

Mg3N2

Only add one atom at a time, as necessary, until finished

Calcium Nitride

Ca3N2

Aluminum Sulfide

Al2S3

Understanding the previous problems is very important—you must be able to trace the electrons as

they leave the metal and go to the non-metal in the formation of these ionic bonds. However, there is a

faster method of determining the formula for ionic compounds.



When we write the ionic charges next to the formulas, an interesting pattern appears.

11. Complete the table. Chemists don’t usually write “1”s, but we will write them here. Also, be sure to

write the charges as superscripts and how many there are (quantity) as subscripts.

12. Write an EVIDENCE and a CLAIM (based on the evidence) from the table above.

Evidence Claim

Any example from above

Total (+) charge must equal total (-) charge

Number of electrons lost MUST EQUAL number of electrons gained

Symbol of cation always written FIRST

Symbol of anion always written SECOND

Use CRISS-CROSS method short-cut

method to determine correct formula

Remember to simplify subscripts!

The pattern of dropping the signs from the charges and switching the numbers to give you the formula

could be called the SWITCHEROO Pattern. The following shows how we can apply this pattern to

aluminum sulfide:

Step 1: Find the Ionic Charges Al3+ S2-

Metal Nonmetal Ionic Charge on

the Metal Ionic Charge on the Nonmetal Chemical Formula

Sodium Chlorine Na1+ Cl1- Na1Cl1

Magnesium Bromine Mg2+ Br1- Mg1Br2

Iron (III) Oxygen Fe3+ O2- Fe2O3

Copper (II) Nitrogen Cu2+ N3- Cu3N2

Aluminum Iodine Al3+ I1- Al1I3

Magnesium Nitrogen Mg2+ N3- Mg3N2



Step 2: Drop the signs and switch the numbers to make the subscripts Al2S3

You now know two ways of predicting the formula for ionic compounds: the first method is to draw the

valence electrons with arrows showing how they move from the metal to the nonmetal, and the second

method is to switch the numbers (without the signs) of the ionic charges. But, there is something you

must be careful about when using this new pattern.

13. Find the chemical formula for magnesium oxide. Use both methods that we have learned.

Method 1: Draw the electron dot diagram for each element and show (using arrows) where the

electrons will transfer to, then predict the chemical formula.

Name Chemical Formula Diagram

Magnesium Oxide MgO

Method 2: Find the ionic charges for each element, and switch the numbers (without the signs).

Step 1: Find the Ionic Charges Mg2+ O2-

Step 2: Drop the signs and switch the numbers to make the subscripts

Mg2O2 –> MgO

Were the answers the same? Which one is correct?

There is never any need for any adjustments to be made when using Method 1. However, if the ionic

charges have the same (absolute) value, they can be cancelled to one. The correct formula for

magnesium oxide is Mg1O1 (although chemists don’t write the “1”s).

But what happens when the charges have a common factor?

14. Find the chemical formula for manganese (IV) oxide. Use both methods we have learned.

Method 1: Draw the electron dot diagram for each element and show (using arrows) where the

electrons will transfer to, then predict the chemical formula.

Name Chemical Formula Diagram



Manganese Oxide MnO2

Method 2: Find the ionic charges for each element, and switch the numbers (without the signs).

Step 1: Find the Ionic Charges Mn4+ O2-

Step 2: Drop the signs and switch the numbers to make the subscripts

Mn2O4 MnO2

Which answer is correct? When using the SWITCHEROO method and there is a common factor in the

ionic charges, you must simplify the ratio. The chemical formula for manganese (IV) oxide is Mn1O2.

Whatever method you choose to use, remember that ionic bonds represent a transfer of electrons from

the metal to the nonmetal. This complete transfer results in the formation of a positive cation (the

metal) and a negative anion (the nonmetal).

Ionic bonds are a result of large differences in the electronegativity of the two elements . . . in other

words, the nonmetal (with a high electronegativity) pulls electrons much more than the metal (with a

low electronegativity).


Bond, Covalent Bond 11

Section 3.2 Bond, Covalent Bond Directions for the Student:


Objectives: 1. Describe how covalent bonds are formed. 2. Differentiate between a polar covalent bond and a non-polar covalent bond.

Describe some effects of each type of bond. 3. Predict the type of bond formed between two elements when given the elements'

electronegativities. 4. Predict the chemical formula for molecules forming covalent bonds. Name the

molecule formed. 5. Differentiate between single, double and triple covalent bonds. 6. Use electron dot diagrams to explain how the valence electrons are arranged in

covalent bonds. 7. Draw stick diagrams to represent covalent bonds.

Nonmetals are found in the upper right-hand corner of the periodic table. From our study of ionic

bonds, we know how many times each nonmetal can bond—it will bond until it has a complete

outermost shell.

1. Complete the table by predicting the number of times these common nonmetals can bond.

If ionic bonds transfer electrons from one element (the metal) to another (the nonmetal), what will

happen when two nonmetals bond? Nonmetals have a high electronegativity (they pull electrons with a

large force).

2. Predict what will happen if two nonmetals bond.

Instead of transferring electrons like in ionic bonds, there will now be a sharing of the electrons forming a covalent bond

Element Valence Number

Number of additional electrons required to complete

valence shell Number of times element

can bond

Carbon 4 4 4

Nitrogen 5 3 3

Oxygen 6 2 2

Fluorine 7 1 1

Sulfur 6 2 2

Chlorine 7 1 1



When two nonmetals bond, they share a pair electrons in a covalent bond. A covalent bond is

significantly stronger than an ionic bond. As a result, covalent bonds do not break apart (disassociate) in

water (aqueous environments).

Sometimes, nonmetals bond with themselves. This example serves as a good introduction to covalent

bonds. While it is still important to be able to draw the nucleus and all of the electrons, we will only

focus on the valence electrons, as that is where the electrons are that form chemical bonds.

3. Draw the electron dot diagram (just the valence electrons) for chlorine. Since there are two

chlorine atoms, draw the first electron dot diagram using small dots (like normal) and draw the

second electron dot diagram using small “x”s. (It is recommended that you place the one spot

without an electron in between the two atoms.)

Cl Cl

Next, without adding anymore electrons, find a way to make the valence shells complete on BOTH

fluorine atoms.

F F

Finally, around each atom draw a circle that is just outside all of the electrons that count for that

atom. Does each atom meet the requirements for the Octet Rule?



By sharing electrons, a covalent bond can make it seem as though there are more electrons than there

really are. Each atom requires 8 valence electrons in its outermost shell to be stable (the Octet Rule),

which means there should be a total of 16 valence electrons drawn, right? But by sharing a PAIR OF

ELECTRONS, a covalent bond can make 14 valence electrons seem like 16 valence electrons.

This is an example of a diatomic (di- means two) molecule that is also homonuclear (homo- means

same), which means the two atoms that are joined are of the same element.

There are seven elements that form homonuclear diatomic molecules:

hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine. Since

chlorine and fluorine are in the same column, the electron dot diagram

for F2 will be identical to that of Cl2 (with the exception of the chemical

symbols, of course).

When two atoms share a pair of electrons, forming a covalent bond, we

often draw a stick to represent that pair of shared electrons.

4. Draw a covalent bond, represented only by a stick, between two fluorine atoms.

F F

This is how chemists represent a SINGLE BOND. This is called a single bond, but it is a PAIR of electrons

(one electron from one atom, and another electron from the other atom).

Again, since chlorine and fluorine are in the same column and have the same

number of valence electrons, the diagram for chlorine would look like just like

that of fluorine.

Single bonds are very common, but there are also double and triple covalent bonds.

5. Understanding how bonds are created and how to describe them are an important part of

Chemistry. Answer the following questions about bonds.

If a single bond is between two atoms that share one pair of electrons, predict how many pairs of electrons will be shared in a double bond and in a triple bond.

Two, three



A single bond is between two atoms that share a pair of electrons. A double bond is between two atoms that share how many electrons?

two

A triple bond is between two atoms that share how many electrons?

three

When an oxygen atom forms a diatomic molecule with another oxygen atom (a homonuclear diatomic

molecule), two pairs of electrons are shared, forming a double bond. The electron dot diagram below is

already completed on the first oxygen atom.

6. Complete the electron dot diagram for the other oxygen atom, showing how there are two pairs of electrons between the two oxygen atoms. (It is recommended that you draw the electrons around the second oxygen in a mirror image to the one already completed.) Then, for each atom, draw a circle around the electrons that are counted for that atom, and satisfy the Octet Rule for each.

7. If a single bond is represented by one stick, predict what a double bond will be represented by.

two sticks

8. Draw a double bond between two oxygen atoms with sticks (and their chemical symbols).

The greatest number of bonds that two nonmetals can share between them is 3. A triple bond shares 3

pairs of electrons, and occurs in the diatomic homonuclear molecule N2. Metallic bonds formed by two

transition metals may form a quadruple bond, but two nonmetals will not. Do not confuse a quadruple

bond with an atom bonding four times. For example, carbon will bond four times, but not all four bonds

will be formed with one other atom.

9. When a nitrogen atom forms a diatomic molecule with another oxygen atom (a homonuclear

diatomic molecule), three pairs of electrons are shared, forming a triple bond. The electron dot

diagram is already completed on the first nitrogen atom. Complete the electron dot diagram for

the other nitrogen atom, showing how there are two pairs of electrons between the two nitrogen

atoms. (It is recommended that you draw the electrons around the second nitrogen in a mirror



image to the one already completed.) Then, for each atom, draw a circle around the electrons

that are counted for that atom, making sure to satisfy the Octet Rule for each.

10. Draw a triple bond between two nitrogen atoms with sticks (and their chemical symbols).

The molecules that we have studied so far are made of the same element. This means that they both

pull the electrons with the same force . . . there is no difference in their electronegativities. This means

that the atoms involved share their electrons very evenly with each other, and will not become charged.

Covalent bonds that are comprised of elements with similar or the same electronegativities and,

therefore, pull the electrons very evenly, share the electrons evenly and are called nonpolar covalent

bonds.

In ionic bonds, the electron was transferred from the metal to the nonmetal, forming charged atoms, or

ions. Nonpolar covalent bonds involve a more equal sharing of the electrons, so neither atom will

become charged. They are called “nonpolar” because the atoms do not have slightly different charge . . .

there are no poles of opposite charges on the ends of the molecules.

But this is not always the case. Sometimes, two atoms will only partially share their electrons.

11. Hydrogen has a somewhat strong pull on electrons, but it is not nearly as strong as oxygen’s pull on electrons. Oxygen will pull electrons to its outermost shell with a stronger force than hydrogen. Predict what will happen to the valence electrons if two hydrogen atoms bond with an oxygen atom.

Because the oxygen atom is larger than the hydrogen atom, its attraction for the hydrogen's electrons is correspondingly greater so the electrons are drawn closer in to the orbit of the larger oxygen atom and away from the hydrogen orbits.



Since hydrogen does not pull an electron as much as oxygen, the

electrons will spend more time near the oxygen atom. This is not a

complete transfer of the electrons, so the oxygen does not get a

FULL additional negative charge from the extra electrons. Instead,

the oxygen just get a partial negative charge and the hydrogen gets

a partial positive charge. This partial charge is designated with a “δ”, the lower case Greek symbol for

delta.

This molecule has partial charges on it, with opposite poles. The oxygen end has a slight negative charge,

and the hydrogen end has a slight positive charge. As such, molecules that do not share electrons

evenly are called polar covalent bonds because they have different poles (or ends) with opposite

charges.

Notice that when you draw the circles around the atoms to show which electrons count for each atom,

you will only circle two electrons for hydrogen.

12. Why is hydrogen stable with only two electrons in its outermost shell?

For stability, an atom tries to reach the electronic configuration (arrangement of electrons in orbits) of the nearest noble gas. The noble gas nearest to Hydrogen is Helium. So, it gains 1 electron to get Helium's configuration which is 2 electrons.

13. Draw H2O (water) using a stick model. Use the electron dot diagram of water as a guide. Add the partial charges where necessary.

Generally speaking, metals bonding with nonmetals will form ionic bonds and nonmetals bonding with

nonmetals will form covalent bonds. However, that is only a generalization. To be certain what type of

bond is formed, one should always check the difference in the electronegativities.



Electronegativity for Bonding Elements

Note: These numbers may vary, depending on which scale you use and which sources you reference, but

the trends remain the same. (Note: These ranges may slightly vary, depending on which source you

reference.)

Difference in Electronegativity Type of Bond

0.0 – 0.3 Nonpolar Covalent

0.4 – 1.7 Polar Covalent

1.8 – 3.3 Ionic

14. Using the table with the electronegativities, what happens to the electronegativity value as you move up a column?

It increases

15. What happens to the electronegativity value as you move right, across a row?

It increases

16. Determine what type of bond is formed when these two elements bond. Write the larger of the two

electronegativities first when subtracting to avoid a negative value.



17. Draw NH3 (ammonia) using an electron dot molecule. Circle the electrons that count for each atom. (Hint: Draw nitrogen with a pair of electrons on one side and only one electron on the other three sides.)

18. Draw a stick model for NH3 and determine what type of bond is formed. If necessary, put partial charges in the proper places.

19. Draw CO2 using an electron dot diagram and stick model. Remember that, in order to have a stable electron arrangement, carbon must bond 4 times and each oxygen must bond 2 times. (Hint: Start by drawing carbon in the middle of the oxygen atoms, and put a pair of electrons on carbon’s right and left.)

Element 1 Element 1

Electronegativity Element 2 Element 2

Electronegativity Difference in

Electronegativity Type of

bond

Sodium 0.9 Chlorine 3.0 3.0 – 0.9 = 2.1 ionic

Hydrogen 2.1 Carbon 2.5 2.5 – 2.1 = 0.4 Polar Covalent

Chlorine 3.0 Bromine 2.8 3.0 – 2.8 = 0.2 Covalent

Hydrogen 2.1 Oxygen 3.5 3.5 – 2.1 = 1.4 Polar Covalent

Fluorine 4.0 Fluorine 4.0 4.0 – 4.0 = 0 Non-Polar Covalent


Functional Groups 19

Section 3.3 Functional Groups Directions for the Student:


Objectives: 1. Differentiate between a functional group, a free radical and a polyatomic ion. 2. Identify and describe the significance of six biologically important functional groups

(hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, and phosphate).

Organic molecules are carbon-based. This means that they often have long backbones of carbon,

forming molecules that are long chains. But not all of the atoms along this long chain are reactive. In

fact, the molecule may be very stable, with only one area that is reactive. This area is called a functional

group, and it determines how the molecule will behave chemically (react and bond).

A functional group is different from a polyatomic ion or a radical. See if you can tell how.

1. Complete the table.

Notes Drawings Questions

Hydroxide Ion—

I notice that…

Hydroxyl Radical—

I notice that…

Hydroxy Group—

I notice that…

1. Which one has a charge?

2. Which one is part of a larger molecule and is attached to more atoms?

3. Which one has an unpaired valence electron that makes it very reactive?

Ions are atoms or groups of atoms that have gained or lost an electron. This means that there are no

longer equal numbers of charged particles (positive protons and negative electrons), so there is an

overall charge. Groups of two or more atoms bonded together that have an overall charge are called

polyatomic ions—these usually act as one unit as they react, with the charge being spread over the

entire polyatomic ion.



Free radicals (often referred to as simply “radicals”) have an unpaired valence electron. This means that

the atom does not have a stable electron arrangement, and is not following the Octet rule. In the

hydroxyl radical, the unpaired valence electron on oxygen means that oxygen only has seven electrons

in its outermost shell. When this oxygen is given a chance to react and gain that last electron that it

needs to become stable, it will do so—this makes it very reactive.

Functional groups are groups of atoms within a larger molecule that are more reactive than other areas

of the molecule, and determine how the overall molecule will react. There are six important functional

groups in Biology that greatly affect living organisms. These functional groups determine the chemical

behavior of the molecules that are the basis for life as we know it.

The hydroxy group (often referred to as the hydroxyl group) shows that it is part of a larger molecule

with a large stick off the side of the oxygen atom. This functional group plays a large role in determining

how the entire molecule will behave.

2. Examine the molecule below. There are usually so many carbon atoms in biomolecules (organic

molecules are carbon-based) that chemists don’t like to write the “C”s. Instead, we have to remember

that there is a carbon wherever two lines (bonds) meet.

Identify all of the hydroxyl groups by marking each one.

Notice that this molecule has three phosphate groups, a 5-carbon sugar (ribose) and a nitrogenous base

(adenine). This molecule is often called the energy currency of the cell.

3. What is the molecule pictured in #2? Adenosine Triphosphate (ATP)

Hydroxyl functional groups play a very important role in dehydration synthesis, which forms larger

molecules from smaller molecules by removing a water molecule.

Monosaccharide—OH + H—Monosaccharide Disaccharide + H2O

4. Explain the role of the hydroxy group in dehydration synthesis.

The hydroxy group can combine with a hydrogen atom from the other molecule to form water, leaving an unbounded atom on each molecule, allowing them to bond.



Functional groups are more reactive than other areas of the larger molecule. Oxygen is more

electronegative (pulls the electrons more) than hydrogen, making partial charges on each atom and

increasing its reactivity. This means that the electrons that are “shared” in the covalent bonds are held a

little more closely to the oxygen atom than to the hydrogen atom (making a “polar” covalent bond with

ends that have opposite partial charges).

Another important functional group is the carbonyl group. This group is simply a carbon that has a

double bond with an oxygen atom. Oxygen is very electronegative, and it pulls the electrons with more

force than the carbon atom.

5. Identify carbonyl group in the molecule with a mark over the top of the molecule where the carbonyl group is. How many carbonyl groups are there in this molecule?

There is only one carbonyl group in this molecule.

6. Identify a similarity and some differences between these molecules:

Remember that “R” simply stands for the Rest of the molecule (a side group), which could be many atoms or simply just one atom. R’ means that it leads to another set of atoms and is said as “R prime” (you may have two or more “Rests” of the molecules).

Both molecules have a carbonyl group coming off of the central carbon. The molecule on the left only has one R-group while the molecule on the right has two R-groups.

Students will learn that the molecule on the left is an aldehyde and the molecule on the right is a ketone later.

While both of the molecules from #6 have a carbonyl group, the molecule on the left only has one R-

group while the molecule on the right. An aldehyde is a carbonyl functional group that has at least one

hydrogen attached to it (with only one side group), while a ketone is a carbonyl functional group that

has two side groups attached to it

Formaldehyde (simplest of the aldehydes) Acetone (used for cleaning in the laboratory)

It is possible to have more than one functional group on the same molecule. In fact, some functional

groups combine to form a larger, and differently named, functional group all together.



7. Examine the molecule. What functional groups can you identify?

This molecule has a hydroxyl functional group and a carbonyl functional group.

Sometimes two functional groups can combine to make a new functional group. When both a hydroxyl

functional group and a carbonyl functional group are found together, they are called a carboxyl group.

Even the name “carboxyl” is a combination of the two smaller functional groups.

Because this group can donate a proton (a hydrogen ion, or H+), it is an acid. An organic compound with

a carboxyl group on it is referred to as a carboxylic acid. There are many different groups of atoms that

can on the “R” group of this molecule, which means there are many carboxylic acids. This group is

usually written as “-COOH” (with the stick showing that it is bonded with other atoms).

8. Carbonic acid is pictured below. It plays a very important role in our blood by keeping the acid-base system balanced (in homeostasis) and transports CO2

out of the blood stream. What functional group does carbonic acid have on it?

Carbonic acid has a carboxyl group on it.

9. Carbonic acid is also called “acid of the air” because it can result from carbon dioxide dissolving in water (making the water more acidic). Write an equation that shows water and carbon dioxide combing to form carbonic acid. Use double arrows (⇌) to show it can go back and forth to find an equilibrium (or balance).

CO2 + H2O ⇌ H2CO3

Students may also write carbonic acid as HOCOOH since it was stated that the carboxyl group is written as -COOH.

Without this system, we would not be able to remove carbon dioxide from our blood stream, and it is

also why the oceans can absorb so much carbon dioxide from the air (which makes the oceans more

acidic).

So far, we have only seen functional groups that use carbon, oxygen and hydrogen. But the next

functional group uses nitrogen.

Amine functional groups have a central nitrogen atom. While ammonia (pictured below) is not an amine

because the nitrogen is not bonded to any carbon atoms, it useful as a starting point to think of amines.



The amine functional group has a nitrogen atom that is bonded three times (at least once to carbon) and

has a lone pair of electrons, which repel the bonds away, affecting the overall shape of the molecule.

(Do not confuse a “lone pair of electrons” with an unpaired valence electron—like on a free radical—

that is very reactive.)

When one of the three hydrogen atoms of ammonia is removed and replaced with a carbon compound

(represented by an “R” group), a primary amine arises. A secondary amine is bonded to two carbon

atoms. The nitrogen in a tertiary amine has all three of its bonds with a carbon compound.

10. Examine the molecule. What kind of amine is it? How do you know?

This is a secondary amine because it has two carbon compounds bound to the nitrogen.

11. Examine the molecule. What kind of amine is it? How do you know?

This is a primary amine because it only has one carbon compound bound to the nitrogen.

With these distinctions in mind, the most common way to refer to a nitrogen with two hydrogens

bonded to it is by calling it an amino group (which would be a primary amine when bonded with a

carbon compound). These play an important role in the structure of DNA, forming part of the

nitrogenous bases (adenine, guanine, cytosine and thymine).

12. Here is cytosine, a nitrogenous base on DNA. What functional group is on position 4?

The functional group at position 4 is an amino group.

Amino groups are found in many places, but none probably more important than amino acids, the

building blocks of proteins. (Take a moment to give the proper worth to proteins that they are due—

proteins, after all, make the vast majority of your body’s structures.)

In another combination of functional groups, an amino group and a carboxyl group (bonded around a

central carbon with an R group) together form an amino acid. Amino acids then bond with other amino

acids using peptide bonds, forming into polypeptides and proteins.



13. Here is a basic structure on an amino acid. What parts of the amino acid are the same on all amino acids and what part differs on different amino acids?

The amino group, the central carbon, and the carboxyl group are common to all amino acids. The R group varies from amino acid to amino acid and determines what amino acid it is.

14. What functional group on “Amino acid 1” detaches to allow for the formation of the peptide bond with “Amino acid 2”? (Choose the smaller functional group, not the carboxyl group.)

The functional group on “Amino acid 1” that detaches to allow for the formation of the peptide bond is the hydroxyl functional group, which is part of the carboxyl functional group.

15. This reaction links together two molecules to create a larger molecule. What is the other product of this reaction?

Water (H2O) is the other product of this reaction.

16. This is called a condensation reaction, but can also be referred to by a different name. What is this type of reaction called that forms a new substance by combing two smaller molecules while removing water? (When naming this reaction, think about what you are if you don’t have enough water in your body.)

This type of reaction can be called a dehydration synthesis reaction.

Proteins are polymers, which means they have repeating subunits, like trains have cars. Proteins have

repeating amino acids, which means that amino acids are the monomers for proteins. By releasing the

hydroxyl group from one amino acid and a hydrogen atom on the amino group from the other amino

acid, this dehydration synthesis reaction forms a new compound while releasing water. This is one of the

most important reactions in all of biology, helping to form proteins and other biological polymers.



The order of amino acids determines how the protein will behave chemically. But the bonds that link the

amino acids are not the only important bonds. These polypeptide chains that form during dehydration

synthesis are often very long—so long that they curl back on themselves and form additional bonds that

also determine chemical behavior.

17. Examine this polypeptide chain. What element is joining parts of the chain with other parts?

The polypeptide chain is joined with sulfur atoms to other parts of the chain.

The molecule pictured above is cysteine, which is an amino acid. Notice that it has the two usual

functional groups that all amino acids have. (If you do not know what these are, please go back and

review at this time.)

However, cysteine also has a sulfur atom bonded to a hydrogen atom as part of its “R” group (or side

chain). The sulfur and hydrogen atoms form a functional group called a thiol group, or a sulfhydryl

group. The thiol group is similar to a hydroxyl group, except that oxygen is replaced with sulfur.

18. Examine the amino acid cysteine. What functional groups can you find on it? Which ones are found on all amino acids?

The functional groups found on cysteine are the carboxyl group (which is made of a hydroxyl group and a carbonyl group), an amino group, and a thiol group. The carboxyl group and the amino group are found on all amino acids, but the thiol group is specific to cysteine.

When the amino acid cysteine is used in a polypeptide chain (protein), the thiol groups link up with

other thiol groups to form a disulfide bond. This bends and molds the protein into a specific shape

which allows it to perform specific jobs around the cell.

The disulfide bond, which is also called an SS-bond, is usually written as R-S-S-R’ showing the two R

groups off to either side of the sulfur atoms.



The final functional group important to biological organisms is the phosphate group. Similar to the other

functional groups, the phosphate group plays an important role in a macromolecule. (The important

biological macromolecules are carbohydrates, lipids, proteins and nucleic acids.) All nucleic acids (which

are DNA and RNA) have a sugar-phosphate backbone, depending on the phosphate group for their

structure.

A Nucleotide [Author: OpenStax]

Nucleic acids (like proteins) are polymers, which means they have repeating subunits, like trains have

cars. The repeating subunit for nucleic acids are nucleotides (shown above). In this case, the sugar is

deoxyribose, which means this must be part of a DNA molecule since the sugar for RNA is ribose. The

nitrogenous base is guanine—there are four possible nitrogenous bases found on DNA: guanine,

cytosine, adenine and thymine.

19. What are the three parts of a nucleotide? The three parts of a nucleotide are a phosphate group, a sugar and a nitrogenous base.

[Author: OpenStax]

As you look along the “Sugar-Phosphate” backbone, you see why that is a perfect name for this

structure. DNA is a double-stranded molecule, like a twisted ladder, with the sugar-phosphate

backbones as the legs and the nitrogenous bases forming the rungs.



20. Of the three parts of the nucleotide (sugar, phosphate, and nitrogenous base), which part is always the same, regardless if it’s on DNA or RNA.

The phosphate is the only part of a nucleotide that is always the same. DNA and RNA have different sugars, and there are 5 different nitrogenous bases.

DNA has deoxyribose for its sugar, while RNA has ribose for its sugar. DNA has cytosine, guanine,

adenine and thymine for its nitrogenous bases, while RNA replaces thymine with uracil. The only part of

DNA and RNA that is always the same is the phosphate group that makes up part of the backbone.

Another extremely important way a phosphate group plays an important role in biology is in the energy

currency for the cells.

Cellular processes need energy, but the energy-storing molecule (glucose) is too unwieldy and large to

be of much use to the cell. Instead, the energy from glucose must be converted to a more usable form:

adenosine triphosphate.

Adenosine Diphosphate Adenosine Triphosphate

Adenosine diphosphate (ADP) is like a partially charged battery. By linking one more phosphate onto

ADP, adenosine triphosphate (ATP) is formed and is able to supply energy to cellular process.

21. How many phosphate groups does ADP have? How many phosphate groups does ATP have?

ADP has two phosphate groups, while ATP has three phosphate groups.

22. Noticing that ATP and ADP both have a nitrogenous base (the two rings in the upper right), a sugar (the large pentagon) and a phosphate group, what kind of molecule are ADP and ATP?

Both ADP and ATP are nucleotides.

23. When ATP releases its energy for cellular processes, it also releases a phosphate group. With this in mind, where was the energy stored in the ATP molecule?

ATP stores its energy in the bond that links the final phosphate group.

Linking that third phosphate group onto ADP to form ATP is one of the most important steps in all of

biology and is called phosphorylation. There are three major ways phosphorylation occurs:

photophosphorylation (in photosynthesis), substrate-level phosphorylation (like in glycolysis), and

oxidative phosphorylation (in the electron transport chain during cellular respiration).


Hydrogen Bonds—Making Water Amazing 28

Section 3.4 Hydrogen Bonds—Making Water Amazing Directions for the Student:


Objectives: 1. Describe conditions necessary for and the characteristics of hydrogen bonds. 2. Analyze the structure of water molecules and explain the results of their hydrogen

bonds. 3. Describe characteristics of water, including solvency, increasing chemical reactivity,

thermal stability and lubrication.

Polar covalent bonds are still covalent bonds, they just don’t share their electrons evenly. As a result,

there are partial charges on the atoms, and, as we all know, opposites attract.

Hydrogen usually does not pull the electrons as much as the atoms it bonds with. This means that

hydrogen atoms in polar covalent bonds will have a slight positive charge, and will be attracted to atoms

with a slight negative charge. This is called a hydrogen bond, but it is really just an attraction between

the polar ends with opposite charges.

1. Draw two water (H2O) molecules using sticks to show the bonds. Then draw the partial charges (with a lower case delta: ᵟ ) where appropriate. Add a dashed line between two polar ends with opposite charges to represent a hydrogen bond.

2. Predict what will happen when many water molecules get together. Specifically, discuss what will happen to the water as a collective group.

When water molecules align with each other, a weak bond is established between the negatively charged oxygen atom of one water molecule and the positively charged hydrogen atoms of a neighboring water molecule. The weak bond that often forms between hydrogen atoms and neighboring atoms is the hydrogen bond. Hydrogen bonds give water molecules two additional characteristics: cohesion and surface tension. Because of the extensive hydrogen bonding in water, the molecules tend to stick to each other in a regular pattern. This phenomenon, called cohesion, is easily observed as you carefully overfill a glass with water and observe the water molecules holding together above the rim until gravity overtakes the hydrogen bonding and the water molecules spill down the side of the glass. Likewise, the cohesive property of water allows tall trees to bring water to their highest leaves from sources below ground.



Water has an amazing ability to stick together. The hydrogen bonds formed between two molecules of

water give water great cohesion. But water doesn’t just stick to itself—it also sticks to other things.

Think about how much water sticks onto you when you get out of the swimming pool. The hydrogen

bonds help give water great adhesion too. (Think of adhesive tape sticking things together.)

Water is known as the universal solvent. Many things dissolve in water (think of adding salt to water and

watching it seemingly disappear). Solutions that have water as their solvent are referred to as aqueous

solutions, and life depends on them. Because water is polar, it can easily dissolve other polar things,

which is why ionic compounds like salt will break apart in water. Now that the ions are disassociated,

they can undergo chemical reactions.

3. Examine the data below for a reaction and write an EVIDENCE and CLAIM.

Amount of Water Added Time Required for Reaction

0 mL Did not react

5 mL 15 seconds

10 mL 5 seconds

Evidence Claim

No water = no reaction

The more water = faster reaction time

Water is required for the reaction to occur

Water speeds up the reaction time

If the particles are not dissolved in water, they may not react. And if they are not completely dissolved in

water, the reaction time will not be as quick—water increases chemical reactivity.

4. Examine the data below. The data is taken from two equal parts of water and soil (land) that were exposed to equal amounts of sunlight (energy. Complete an EVIDENCE and CLAIM.

Time Land Temperature (ᵒF) Water Temperature (ᵒF)

0 minutes 55 ᵒF 55 ᵒF






Evidence Claim

No exposure time = no change in temperature

More exposure time = higher changes in temperature

Time must be given for reactions to occur

The greater the exposure time = higher measured reactions

It takes a significant amount of energy to change the temperature of water—in other words, water has a

high heat capacity. This means that once water absorbs the heat, it keeps it. Also, when you sweat and

convert liquid water into gaseous water (or water vapor), it takes a lot of heat away from your body,

thereby, cooling you off!

5. Examine the data table below that measures the friction between two surfaces with different amounts of water between them, and make an EVIDENCE and CLAIM based on the data.

Amount of Water Between Two Surfaces Amount of Friction (newtons)

0 mL 5 N

5 mL 4 N

10 mL 3 N

15 mL 2 N

Evidence Claim

No water = high amount of friction

The higher the amount of water = lesser friction

Water must be present to reduce friction

Water functions as a lubricant

There are many parts of your body that rub against another part of your body. Without the lubrication

that water provides, any kind of movement would be difficult, at best.

Water is vital to life. Water helps us digest food, moves nutrients around our bodies, removes wastes,

send electrical messages in muscles and nerves, lubricates our moving parts, and regulates our body

temperatures. The chemical properties of water, including its hydrogen bonds, high heat capacity and its

ability to stay in its liquid form over a wide range of temperatures, give water amazing abilities and life

as we know it could not exist without water.


Solutions and Their Attributes 31

Section 3.5 Solutions and Their Attributes Directions for the Student:


Objectives: 1. Describe the criteria used to define solutions, colloids and suspensions. 2. Identify three different types of “mixtures” through a verbal description, criteria or

through images. 3. Define and review the following terms: mole, concentration, molarity, solute,

solvent, Avogadro’s constant, buffer, homeostasis, osmosis, ion, acidic, basic, alkaline, neutral, and sodium chloride (NaCl).

4. Complete a Molarity calculation. 5. Describe how pH is determined and explain some characteristics of an acid and a

base. 6. Define a buffer and describe the importance of buffers used in allied health.

Substances get mixed up a lot in daily life. These mixtures have important biological consequences, and

are generally grouped into three categories: solutions, colloids and suspensions.

To understand this better, let’s look at something we all have: blood.

Component of Blood Approximate % Volume

in Blood

Size of Component

(nm = nanometer and µm = micrometer)

Water 50.6% 0.28 nm = 0.00000000028 m

H+ <0.1% 0.10 nm = 0.00000000010 m

Na+ <0.1% 0.18 nm = 0.00000000018 m

K+ <0.1% 0.22 nm = 0.00000000022 m

Ca+ <0.1% 0.18 nm = 0.00000000018 m

Cl- <0.1% 0.18 nm = 0.00000000018 m

HCO3- <0.1% 0.16 nm = 0.00000000016 m

Lipids <0.5% 2 to 5 nm = 0.000000002 m

Glucose <0.5% 0.8 nm = 0.0000000008 m

Amino Acids <0.5% 0.8 to 1.4 nm = 0.0000000008 m

Proteins 3.8% 15 to 20 nm = 0.000000015 m

Platelets <0.1% 2 µm = 0.000002 m

White Blood Cells <0.1% 10 µm = 0.000010 m

Red Blood Cells 44.9% 5 µm = 0.000005 m



The main component of a mixture is the dispersion medium. All of the other components are

considered to be dispersed throughout the main component.

1. What is the dispersion medium of blood? Water

2. What is the range (smallest to largest) of the different components of blood?

0.10 nm – 10 µm

Scientists classify mixtures into three categories, based on the size of the component. The type of

medium you are dealing with depends on the size of the particle.

Particle Size Type of Mixture

Less than 1 nm Solution

1 nm – 1 µm Colloid

Greater than 1 µm Suspension

3. Using the table as a guide, review each component listed and determine what type of mixture it would be when it is mixed with water.

Component Size Type of Mixture

H+ 0.10 nm Solution

Ca+ 0.18 nm Colloid

Lipids 2 to 5 nm Colloid

Glucose 0.8 nm Solution

Platelets 2 µm Suspension

Red Blood Cells 5 µm Suspension

4. What type of mixture is blood? solution, colloid, and suspension

Blood is an unusual mixture—it is a solution, a colloid and a suspension.

Solutions are very important mixtures. As such, the parts of the solution get special names. The medium

doing the dissolving (usually water) is called the solvent. The particles (which are less than 1 nm) that

are dissolved in the solvent are called solutes.

5. What particles in blood are considered to be solutes? List all of them.

Water, H+, Na+, K+, Ca+, Cl-, HCO3-, Lipids, Glucose, Amino Acids



Knowing how to work with solutions is very important in biology and chemistry. One way that we

understand solutions is to identify their concentrations, in terms of the number of solutes in one liter

(solutes per liter). This means we have to know the mass of the of the solutes. (Remember that the

MASS NUMBER refers to the number of protons and the number of neutrons combined, and that

different isotopes have different numbers of neutrons. With this in mind, the average atomic mass is an

average of all of the isotopes.) But where can we find the mass of individual atoms?

Once again, the periodic table comes to the rescue.

Below each element is its average atomic mass (given in atomic mass units or amu). Because we don’t

always know exactly which isotope it is, we will use the average atomic mass. There may be times when

you do know exactly which isotope is being used. Using the periodic table as your guide, answer these

questions.

6. The first solute on the list is H+. What is the mass of one hydrogen atom?

1.008 amu

Hopefully you found the “1.008” amu underneath hydrogen on your periodic table. If you did not, make

sure you know where it is now, before moving on.

7. If one hydrogen atom has a mass of 1.008 amu, what is the mass of 2 hydrogen atoms?

2.016 amu

When there are multiple atoms, we can simply multiply by how many there are. Did you multiply 1.008

amu by 2?

8. What is the mass of a sodium atom? (Again, use the average atomic mass.)

22.990 amu

Now we will find the mass of a molecule. Add the mass of each atom together to find the mass of the

molecule.

9. What is the mass of one molecule of sodium chloride (NaCl)?

58.443 amu

One sodium is counted as 22.99 amu and one chlorine atom is counted as 35.4527 amu. Therefore, a

sodium chloride molecule will be 58.4427 amu.

10. What is the mass of ten sodium chloride molecules? 584.43 amu



11. What is the mass of 100 sodium chloride molecules? 5,844.3 amu

Unfortunately, there is not a balance that measures substances in amu’s. What we have been doing is

simply a thought experiment, and it would be extremely difficult to ever measure individual atoms or

molecules. If we only have balances that measure in grams (the ones in our labs usually measure to a

hundredth of a gram), how could we possibly use grams to approximately know how many molecules

there are in a sample? What do we need to solve this dilemma? (Think about these questions for a

moment before moving on.)

If we know how many atoms are in amu’s and can only measure in grams, we have to have a bridge

between amu’s and grams. We must have a conversion from amu’s to grams. But what is this magical

number that can convert amu’s to grams?

To understand this magical number, let’s do another thought experiment. Imagine you went outside and

started to catch individual carbon atoms and put them onto a scale as you counted them. While you

added more and more (1, 2, 3, 4, 5, . . . ) carbon atoms, when you reached a certain number, the scale

would read 12.011g.

12. Why is 12.011 an important number for carbon? Refer to your periodic table.

It is the average atomic mass for Carbon

When you get to the point where the scale reads 12.011g of carbon atoms, you will have counted about

602 214 129 000 000 000 000 000 atoms of carbon. (Don’t be confused by the spaces—sometimes

scientists use spaces instead of commas with very large numbers.)

This is the magic number: 6.022 x 1023. It is often called the Avogadro constant, named after the Italian

scientist, Amedeo Avogadro, as tribute for his contributions to science.

The Avogadro constant is also called a mole (abbreviated as “mol”), and it is one of the base units in the

International System of Units.

1 mole = 6.022 x 1023

Instead of saying that we have 6.022 x 1023 particles, we just say that we have 1 mole of particles.

This means that we now have a conversion that will take us from amu’s to grams.

1 gram = 6.022 x 1023 amu’s

13. What is the mass of 1 mole of carbon atoms? 12.011 grams

14. What is the mass of 2 moles of carbon atoms? 24.022 grams



Just as before with more than one atom, if there are multiple moles, we multiply. One mole of carbon is

equal to 12.011g and 2 moles is equal to 24.022g.

15. What is the mass of 1 mole of sodium chloride? 58.44 grams

One mole of sodium has a mass of 22.99g and one mole of chlorine has a mass of 35.4527g, so their

combined mass is 58.4427g

16. What is the mass of 5 moles of sodium chloride? 292.2 grams

17. Glucose is C6H12O6. What is the mass of 1 mole of glucose? Complete the table below first, then answer.

180.162 grams

Element Mass of 1 mole Number of Atoms Total Mass for Element

Carbon 12.011g 6 72.066g

Hydrogen 1.008 grams 12 12.096 grams

Oxygen 16 grams 6 96 grams

Total mass for glucose: 180.162 grams

18. How many moles of sodium chloride (NaCl) are there in 58.4427g?

1 mole

EXAMPLE: How many moles are in 350.6562g of NaCl? Setting up this problem properly is of the utmost

importance.

1 mole of NaCl is to 58..4472g of NaCl as ___x___ moles of NaCl is to 350.6562g of NaCl

1 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙

58.4472𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙=

𝑥 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙

350.6562𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙

350.6562𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙 × 1 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙

58.4472𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙=

𝑥 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙

350.6562𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙 ×350.6562𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙

350.6562𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙 (1 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙)

58.4472𝑔 𝑜𝑓 𝑁𝑎𝐶𝑙= 𝑥 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙

350.6562

58.4472 (1 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙) = 𝑥 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙



6 𝑚𝑜𝑙 𝑜𝑓 𝑁𝑎𝐶𝑙 = 𝑥 𝑚𝑜𝑙 𝑁𝑎𝐶𝑙

There are 6 moles of sodium chloride in 350.6562 grams of sodium chloride.

19. How many moles of carbon dioxide (CO2) are there in 132.027g of CO2? (Hint: First, find the number of grams in one mole of CO2, then set it up like the example.)

3 moles

20. How many moles of H2O are there in 95.4795 grams of H2O? (Hint: The number of moles may not always be a whole number.)

5.3 moles

Now that you understand moles, you can start to examine a very important aspect of solutions:

molarity.

𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑀𝑜𝑙𝑒𝑠

𝑙𝑖𝑡𝑒𝑟

EXAMPLE: There are 3 moles of glucose dissolved into 1 liter of solution. What is the molar

concentration of the solution?

𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑀𝑜𝑙𝑒𝑠

𝑙𝑖𝑡𝑒𝑟=

3 𝑚𝑜𝑙

1 𝐿= 3

𝑚𝑜𝑙

𝐿

This is the same as saying it is a 3 molar solution (or 3 M solution).

21. What is the molar concentration of a solution that has 2 moles of sodium chloride dissolved in 4 liters of solution?

0.5 mol/L



22. What is the molar concentration of a solution with 7 moles of sodium chloride dissolved in 3 liters of solution?

2.3 mol/L

23. What is the molar concentration of a solution with 1 mole of solute in 15 liters of solution?

.06 mol/L

Water is made up of two hydrogen atoms and one oxygen atom. What would happen if you split water

up?

H2O H+ + OH-

Normally, the arrow in the middle stands for “yields” or “turns into” and only points to the right. This

arrow points both ways to symbolize that this reaction can go back and forth, and that is exactly what

happens in water all the time. The “H+” ion is a hydrogen ion and the “OH-“ ion is called a hydroxide ion

(hydrogen and oxygen).

Most solutions in biology are aqueous solutions (solutions with water as their solvent). And we know

that life would not be possible without water. Therefore, understanding the characteristics of water is

very important.

24. When water is split into the hydrogen ion and the hydroxide ion, why are there charges on the ions?

Hydrolysis is a chemical process of adding a water molecule to a compound which most often causes both parts to break their chemical bonds resulting in each fragment becoming either an anion (negatively charged ions like hydroxide ions, OH-) or a cation (positively charged ions like hydrogen ions H+). The oppositely charged ions attach to each other synthesizing into new substances. Often these reactions take place when ionic compounds dissolve in water.

Remembering how strong the oxygen pulls electrons (it has a high electronegativity), it is easy to see

that the oxygen will pull the electron away (making the charge on the hydroxide negative 1) from the

lone hydrogen ion (making the charge on the hydrogen positive 1).



A very common measure of water quality is pH. The pH of a solution is a measure of the molar

concentration of hydrogen ions. Some say that the “pH” stands for the “power of hydrogen”. Most of

the time, the concentration of hydrogen ions is very small.

25. What is the molar concentration of a solution that has 0.01 moles of H+ ions in 1 liter of solution?

o.o1 mol/L

Having a 0.01 M solution may sound like a small amount, but, as we will soon see, that would be a

strong acid.

26. Using the evidence below, complete the two EVIDENCEs and one CLAIM. (Notice that hydrogen ion concentration is abbreviated by [H+]. Brackets are commonly used to denote concentration.)

Hydrogen Ion Concentration (mol/L)

[H+] pH

0.00000000000001 = 1 x 10-14 14

0.0000000000001 = 1 x 10-13 13

0.000000000001 = 1 x 10-12 12

0.00000000001 = 1 x 10-11 11

0.0000000001 = 1 x 10-10 10

0.00000001 = 1 x 10-9 9

0.00000001 = 1 x 10-8 8

0.0000001 = 1 x 10-7 7

0.000001 = 1 x 10-6 6

0.00001 = 1 x 10-5 5

0.0001 = 1 x 10-4 4

0.001 = 1 x 10-3 3

0.01 = 1 x 10-2 2

0.1 = 1 x 10-1 1

1 = 100 0



Evidence Claim

I notice that the concentration is getting larger (as you move down the table) while the pH is getting smaller…

This means that, as the hydrogen ion concentration increases, pH…

I notice that when the hydrogen concentration is written in scientific notation with an exponent, the exponent seems to be related to the pH…

This means that the pH is related to the…

We will study pH more when we study exponents. Seeing the above relationships is a good first step.

Most scales measure the pH scale from 0-14, but it is possible to have solutions with higher or lower

concentrations of hydrogen ions that will result in a pH value of less than zero or greater than 14.

Pure water has a perfect balance of hydrogen ions and hydroxide ions, and it has a pH of 7 (any solution

with a pH of 7 is considered to be pH “balanced”). A solution with a pH below 7 is considered to be

acidic. Any pH above 7 is considered to be alkaline. (Note: A solution with the pH of 8 would be a base,

but we don’t usually say it is basic—rather, we say that solution is alkaline.)

Weak acids will have a pH close to 7. For example, a solution with a pH of 5 or 6 would be a weak acid.

Similarly, weak bases will have a pH close to 7. For example, a solution with a pH of 8 or 9 would be a

weak base. The further away from a pH of 7 you get, the stronger the acid or the base becomes.

Because a pH of 7 has an equal number of hydrogen ions and hydroxide ions, a pH of 7 is considered to

be balanced. Acids have more hydrogen ions and bases have more hydroxide ions.



27. Urine has a pH somewhere around 6 (although it can vary). What type of solution (acid or base) is urine? Does urine (with a pH of 6) have more hydrogen ions or more hydroxide ions? (Remember, there are many other particles that are in urine; pH is just looking at the hydrogen ion concentration.)

Urine is a weak acid. It has more hydrogen ions.

28. Blood has a pH of 7.4, and its variation is quite small. The pH of human blood must remain between 7.35 and 7.45 or there will be severe complications. Is human blood acidic or alkaline? Does blood have more hydrogen ions or more hydroxide ions in it?

Human blood is slightly alkaline. It has more hydroxide ions than hydrogen ions.

29. Cranberry juice has a pH around 2.5, which makes it a somewhat strong acid. Various parts of our metabolism create acids in our bodies. How can we keep our blood pH within that narrow window of 7.35-3.45? What helps regulate changes in pH?

Buffer systems. Urinary, respiratory, and integumentary systems.

30. Complete an EVIDENCE and CLAIM for the data below that shows acid being added to two solutions. Solution A and Solution B are identical in all ways except one. After the EVIDENCE and CLAIM, you will hypothesize about this difference.

Solution A Solution B

Acid Added (ml) pH Acid Added (ml) pH

0 7 0 7

1 6 1 7

2 5.2 2 7

3 4.7 3 6.9

4 4.4 4 6.8

5 4.2 5 6.8

6 4 6 6.7

Evidence Claim

I notice that the more acid added to solution A the faster that the pH drops

I notice that the more acid added to solution B the that the pH drops slower

There is less hydroxide ions in solution A

There is more hydroxide ions in solution B



31. What could cause the difference in the two solutions? (Hint: Think about what acids have excess of.)

There are more hydroxide ions in solution B than A

Acids have a lot of hydrogen ions. Therefore, when acid was added to the solutions, we were essentially

adding extra hydrogen ions. But what happened to those extra hydrogen ions in Solution B?

If the pH didn’t change much that means that the extra hydrogen ions must have bonded with another

atom or group of atoms. If the hydrogen ions are bonded, they are no longer counted in the hydrogen

ion concentration and, therefore, do not lower the pH. In this way, your blood can absorb hydrogen ions

and keep the pH relatively stable. These stabilizing molecules that remove hydrogen ions are called

buffers and we couldn’t live without them.

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