20 sept. 2011 objective: you will be able to: review making calculations and manipulating...

20 Sept. 2011

Objective: You will be able to: Review making calculations and

manipulating measurements Determine the formula for copper

(II) sulfate hydrate Homework Quiz: Week of Sept. 19

How will you know when to stop heating your copper (II) sulfate sample? Why?

Agenda

I. Turn in Problem Set 2II. Problem Set 1: Commonly missed

questionsIII. Finish lab procedureIV. Clean upHomework:Quiz on chapters 1-2: tomorrowLab notebook due Thurs.

Clean Up

CuSO4 in trash All equipment washed and hung up

to dry Ring stands, Bunsen burners and

strikers, etc. back in cabinets Wipe down counters Start planning out your calculations

Homework

Quiz on ch. 1-2 tomorrow!

Safety

Wear goggles until all your equipment has been cleaned and returned.

A hot crucible looks just like a cold crucible! Always use crucible tongs.

Work efficiently but carefully.

Technical notes

Heat the crucible uncovered or with the cover tilted to allow water vapor to escape.

Cool the crucible with the cover on. Cool the crucible in the desiccator

for very best results. Never mass a hot or warm crucible. Oil from your fingers will stick to the

crucible and effect your data.

Work Ethic

Work quickly. If you have “down time,” think: “What can I do now to save time later?”

Set up data tables and calculations while you wait.

This period

Carry out your procedure and collect data.

Begin calculations as soon as you can! Percent of water in the hydrate by

mass. Mole ratio of anhydrous CuSO4 to

H2O in your sample. Work to show how you got your

number of molecules of water of hydration.

Homework

Ch. 2 problem set: tomorrow Quiz on chapters 1-2: tomorrow Lab notebook due Thurs.

21 September 2011

Objective: You will be able to: show what you know about

chapters 1 and 2: calculations and compounds

Do now: Questions?

Quiz

Flip it over when you’re done. Zero tolerance policy for

disruptions. When you finish: Work on lab

calculations silently.

Homework

Check chapter 3 summer assignment answers online: Tomorrow

Lab notebook: calculations: tomorrow

22 September 2011

Take Out: Lab Notebook Objective: You will be able to:

review Avogadro’s number, moles, molar mass, conversions, empirical and molecular formulas

Homework Quiz: 1. How many atoms of silver are equal

to 3.50 moles of silver?2. Calculate the molar mass of silver

nitrate. (Nitrate is NO3-)

Agenda

I. Homework QuizII. Review of Avogadro’s number,

moles, molar mass, conversions, empirical and molecular formulas

III. Challenge problem!Homework: p. 110 #18, 22, 26, 30,

44, 54: Mon.

The Mole

Atoms are so tiny; how do we quantify their masses?

The mole

Mole: The unit for amount of substance

=6.02x1023 atoms or molecules Avogadro’s Number = 6.02x1023

This is equal to the number of atoms of carbon in 12 grams of Carbon-12.

Example

a) How many moles of helium atoms are in 6.46 g of He?

b) How many atoms is this?

Problems

a) How many moles of magnesium are there in 87.3 g of Mg?

b) How many atoms is this?c) Zinc is a silvery metal that is used

in making brass (with copper). How many grams of Zn are in 0.356 mole of Zn?

Sulfur is a nonmetallic element present in coal. When coal is burned, sulfur is converted to sulfur dioxide and eventually to sulfuric acid that gives rise to the acid rain phenomenon. How many atoms are in 16.4 g of S?

Calculate the number of atoms in 0.551 g of potassium.

Molar Mass

The mass of a molecule. Calculate the molar mass of:

sulfur dioxide (SO2) caffeine (C8H10N4O2) methanol (CH4O)

SWBAT convert between grams, moles and number of particles of elements and compounds.

Using Molar Mass

Methane (CH4) is the principal component of natural gas. How many moles of methane are present in 6.07 g of CH4?

Calculate the number of moles of chloroform (CHCl3) in 198 g of chloroform.

Particles, Moles and Mass

1. Calculate the mass of 1.2x1024 molecules of carbon dioxide.

2. How many molecules of glucose are in 2.50x10-3 grams of glucose?

3. Calculate the mass of 1 molecule of water.

4. How many molecules of carbon dioxide are there in 0.0003 grams of carbon dioxide?

SWBAT convert between grams, moles and number of particles of elements and compounds.

Percent Composition by Mass

the percent by mass of each element in a compound. Can be used to determine the

purity of a substance by comparing empirical data to known composition.

Practice Problems

Calculate the percent by mass of each element in hydrogen peroxide.

Phosphoric acid (H3PO4) is a colorless, syrupy liquid used in detergents, fertilizers, toothpastes and in carbonated beverages for a “tangy” flavor. Calculate the percent composition by mass of H, P and O in this compound.

Empirical Formulas

Given the percent composition, you can determine the empirical formula of a compound (reverse of calculating percent composition)

This data is often found by experiment.

Practice Problems

Ascorbic acid (vitamin C) cures scurvy. It is composed of 40.92% carbon, 4.58% hydrogen and 54.50% oxygen by mass. Determine its empirical formula.

A sample of a compound contains 1.52 grams of nitrogen and 3.47 grams of oxygen. The molar mass of this compound is between 90 and 95 g. Determine its molecular formula and accurate molar mass.

More practice problems

1. Determine the empirical formula of a compound having the following percent composition by mass: K: 24.75%, Mn: 34.77%, O: 40.51%

2. A sample of a compound containing boron and hydrogen contains 6.444g of boron and 1.803 g of hydrogen. The molar mass of the compound is about 30 g. What is its molecular formula and exact molar mass?

One more…

Chalcopyrite (CuFeS2) is a principal mineral of copper. Calculate the number of kilograms of copper in 3.71x103 kg of chalcopyrite.

Challenge!

A 0.1005 g sample of menthol (composed of C, H and O) is combusted, producing 0.2829 g of CO2 and 0.1159 g of H2O. What is the empirical formula? (Hint: Be aware that some oxygen in the product comes from the air, and some from the menthol!)

the compound has a molar mass of 156 g/mol what is the molecular formula?

Homework

p. 110 #18, 22, 26, 30, 44, 54: Mon. Finish challenge problem

26 September 2011

Objective: You will be able to: write and balance chemical equations

and calculate mole to mole and mass to mass stoichiometry.

Homework Quiz1. Calculate the mass of 1 atom of

palladium.2. Calculate the empirical formula of a

compound composed of H, O and S, which has 2.1 percent H and 65.3 percent O.

Agenda

I. Homework QuizII. Go over homeworkIII. Review writing and balancing

equations, mole and mass stoichiometry

IV. Practice ProblemsHomework: 112 #60c, e, g, h, k and

l, 64, 66, 71, 74: tomorrowCorrect Quiz for a small quiz grade:

Weds.

Decoding Chemical Equations

2H2(g) + O2(g) → 2H2O(l)

Balancing Chemical Equations

Ex 1. KClO3 KCl + O2

Ex 2. C2H6 + O2 CO2 + H2O

Write and balance:

1. Ammonia gas reacts with oxygen gas to produce nitrogen monoxide gas and liquid water.

2. Solid lithium reacts with nitrogen gas to produce solid lithium nitride.

3. Nitroglycerin (C3H5N3O9) decomposes explosively to produce nitrogen gas, carbon dioxide gas, water vapor and oxygen gas.

4. Carbon dioxide gas reacts with potassium hydroxide to produce potassium carbonate and water vapor.

Mole Ratios

Coefficients indicate the number of moles (or molecules) of each compound

Ex 1. N2(g) + 3H2(g) 2NH3(g)

1. How many moles of hydrogen gas react with 1 mole of nitrogen gas?

2. How many moles of ammonia gas are produced by the reaction of 3 moles of hydrogen gas in excess nitrogen gas?

N2(g) + 3H2(g) 2NH3(g)

3. How many moles of hydrogen gas are required to react with 15 moles of nitrogen gas?

4. How many moles of hydrogen gas are required to produce 25.0 moles of ammonia gas?

5. If 10 moles of nitrogen gas was reacted with 10 moles of hydrogen gas, which would be completely reacted? Which would be excess?

Mass to mass stoichiometric relationships: Ex 1.

The food we eat is degraded in our bodies to provide energy for growth and function. A general equation for this very complex process is:

C6H12O6 + 6O2 6CO2 + 6H2O

If 856 g of C6H12O6 is consumed by a person over a certain period, what is the mass of CO2 produced?

Example 2

All alkali metals react with water to produce hydrogen gas and the corresponding alkali metal hydroxide. A typical reaction is that between lithium and water:

2Li(s) + 2H2O(l) 2LiOH(aq) + H2(g)

How many grams of Li are needed to produce 9.89 grams of H2?

Example 3

Methanol (CH3OH) burns in air according to the equation

2 CH3OH + 3O2 2CO2 + 4H2O

If 209 g of methanol are used up in the combustion process, what is the mass of H2O produced?

Homework

112 #60c, e, g, h, k and l, 64, 66, 71, 74

27 September 2011

Objective: You will be able to: determine which reactant is the limiting

reagent and calculate percent yield. Homework Quiz1. Balance: P4O10 + H2O → H3PO4

2. If 10.0 grams of tetraphosphorus decaoxide is reacted with excess water, calculate the number of grams of phosphoric acid produced.

Bonus: What mass of water reacts with 10.0 grams of P4O10?

Agenda

I. Homework QuizII. Go over homeworkIII. Review limiting reagent and percent

yieldIV. Practice ProblemsHomework: p. 114 #84, 85, 89, 93, 107,

131Correct Quiz for a small quiz grade:

Weds.Ch. 1-3 test Thursday.

Example 4

The reaction between nitric oxide and oxygen to form nitrogen dioxide is a key step in photochemical smog formation:

2NO(g) + O2(g) 2NO2(g)

How many grams of O2 are needed to produce 2.21 g of NO2?

Limiting Reagents Ex 1.

Urea is prepared by reacting ammonia with carbon dioxide:

2NH3(g) + CO2(g) (NH2)2CO(aq) + H2O(l)

In one process, 637.2 g of NH3 are treated with 1142 g of CO2.

a) Which of the two reactants is the limiting reactant?

b) Calculate the mass of (NH2)2CO formed.

c) How much excess reagent (in grams) is left at the end of the reaction?

Example 2

The reaction between aluminum and iron(III) oxide can generate temperatures approaching 3000oC and is used in welding metals:

2Al + Fe2O3 Al2O3 + 2Fe

In one process, 124 g of Al are reacted with 601 g of Fe2O3.

a) Calculate the mass (in grams) of Al2O3 formed.

b) How much of the excess reagent is left at the end of the reaction?

30 Sept. 2010

Objective: SWBAT determine limiting reagent, and calculate percent yield.

Do now: TiCl4(g) + 2Mg(l) Ti(s) + 2MgCl2(l)

If 3.54x107 g of TiCl4 are reacted with 1.13x107 g of Mg, calculate the limiting reagent and the theoretical yield of Ti.

Reaction Yield

theoretical yield: the amount of product that would result if all of the limiting reagent reacted.

actual yield: amount of product actually obtained from a reaction

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28 September 2011 Objective: You will be able to:

practice all chapter 3 skills Homework Quiz

P4O10 + 6H2O → 4H3PO4

1. In the lab, 10.00 grams of tetraphosphorus decaoxide were reacted with 5.00 grams of water. Determine the number of grams of phosphoric acid produced.

2. If 12.5 grams of H3PO4 were produced when this reaction was performed in the lab, calculate the percent yield.

Agenda

I. Homework QuizII. Hand in Quiz CorrectionsIII. Go over homeworkIV. Chapter 3 Problem SetHomework: Ch. 1-3 test Tuesday

(new unit starts tomorrow!)Chapter 3 Problem Set: Tuesday

Percent Yield Ex 1

Titanium is a strong, lightweight, corrosion-resistant metal that is used in rockets, aircraft, jet engines and bicycle frames. It is prepared by the reaction of titanium (IV) chloride with molten magnesium between 950oC and 1150oC:

TiCl4(g) + 2Mg(l) Ti(s) + 2MgCl2(l)

3.54x107 g of TiCl4 are reacted with 1.13x107 g of Mg. a) Calculate the theoretical yield of Ti in grams. g) Calculate the percent yield if 7.91x106 g of Ti are actually obtained.

Ex 2.

Industrially, vanadium metal, which is used in steel alloys, can be obtained by reacting vanadium(V) oxide with calcium at high temperatures:

5Ca + V2O5 5CaO + 2V

1.54x103 g of V2O5 is reacted with 1.96x103 g of Ca. a) Calculate the theoretical yield of V. b) Calculate the percent yield if 803 g of V are obtained.

On the test Classification and states of matter Physical and chemical properties Measurement, handling numbers Dimensional analysis Atomic theory and structure Atomic number, mass number, isotopes Molecules and Ions Chemical formulas and names (incl. acids) Avogadro’s number, moles, molar mass % composition by mass Empirical and molecular formulas Chemical reactions and equations Mole to Mole and Mass to Mass Stoichiometry Limiting reagents, reaction yield

Review Game!

With your partner, solve the problem and show all your work.

Raise your hand when you are done. First group with the correct answer

gets the point and a chance at the bonus point.

An unfortunate tree is carrying on photosynthesis in the forest. One morning, it wakes up with dew on its leaves. The sunshine immediately begins to evaporate the dew. Suddenly, a storm rolls in and a giant wind knocks the tree to the ground. A limb is struck by lighting and partially burns. Over the next year, the remaining parts of the tree rot away. List all the physical changes in one column and the chemical changes in another.

One gallon of gasoline in an automobile’s engine produces on the average 9.5 kg of carbon dioxide. Calculate the annual production of CO2 in kilograms if there are 40 million cars in the US and each car covers a distance of 5000 mi. at a consumption rate of 20 miles per gallon.

A transition metal with 26 protons and 24 electrons forms a bond with a polyatomic ion consisting of phosphorus and four atoms of oxygen with a charge of 3-.

a) What type of bond holds this compound together?

b) Write the name and formula for this compound.

Imagine this compound contains hydrogen instead of iron.

a) What type of compound is it? b) Write the name and formula for

this compound.

Imagine that acid lost one oxygen. Name and write the formula for the newly formed acid.

Calculate the molar mass of this acid, and the percent by mass of each element.

A compound is formed by one carbon atom and four chlorine atoms.

a) What type of bond holds these atoms together?

b) Write the name and formula of this compound.

Carbohydrates contain C, H and O, in which the hydrogen to oxygen ratio is 2:1. A certain carbohydrate contains 40.0% carbon by mass. Calculate the empirical and molecular formulas if the molar mass is about 178 g.

Lysine, an essential amino acid in the human body contains C, H, O and N. In one experiment, the complete combustion of 2.175 g of lysine gave 3.94 g CO2 and 1.89 g H2O. In a separate experiment, 1.873 g of lysine gave 0.436 g NH3. a) Calculate the empirical formula.

b) If the molar mass is about 150 g, calculate the molecular formula.

Hydrogen gas can be prepared by reacting propane gas (C3H8) with steam at about 400oC. The products are carbon monoxide and hydrogen gas. a) Write a balanced equation.

b) How many kilograms of hydrogen gas can be obtained from 2.84x103 kg of propane?

Solid elemental sulfur reacts with a solution of nitric acid to produce a solution of sulfuric acid, nitrogen dioxide gas and water. Write and balance a chemical equation.

When potassium cyanide reacts with acids, a deadly poisonous gas, hydrogen cyanide, is given off.

KCN(aq) + HCl(aq) KCl(aq) + HCN(g)

If a sample of 0.140 g of KCN is treated with an excess of HCl, calculate the amount of HCN formed, in grams.

Nitric oxide (NO) reacts with oxygen gas to form nitrogen dioxide, a dark brown gas.

In one experiment, 0.866 mol of nitric oxide is mixed with 0.503 mol of oxygen gas. Calculate which is the limiting reagent. How many moles of nitrogen dioxide are produced?

When heated, lithium reacts with nitrogen to form lithium nitride.

What is the theoretical yield of lithium nitride in grams with 12.3 grams of lithium are heated with 33.6 grams of nitrogen?

If the actual yield of lithium nitride is 5.89 grams, what is the percent yield?