department of chemistry and biochemistry chm 101 - reeves chm 101 – chapter four properties of...

Department of Chemistry and Biochemistry

CHM 101 - Reeves

CHM 101 – Chapter Four

• Properties of Aqueous Solutions• Precipitation Reactions• Acid Base Reactions• Concentrations of Solutions• Solution Stoichiometry


CHM 101 - Reeves


A solution is a homogenous mixture that consists of • the solvent: the component in the solution present in the largest amount. In aqueous solutions, water is the solvent.• the solutes: the other components in the solution

Electrolytes are solutes that, when dissolved in water, cause the solution to conduct electricity

Properties of Aqueous Solutions


CHM 101 - Reeves

CHM 101 – Chapter Four A solution is a homogenous mixture that consists of • the solvent: the component in the solution present in the largest amount. In aqueous solutions, water is the solvent.• the solutes: the other components in the solution

Electrolytes are solutes that, when dissolved in water, cause the solution to conduct electricity • Strong electrolyte: a compound that, when dissolved in water, dissociates completely into mobile ions that effect the conduction of electricity.• Weak electrolyte: a compound that, when dissolved in water, dissociates only slightly into mobile ions that effect the conduction of electricity.


CHM 101 - Reeves


Water solvates strong electrolytes by surrounding cations with partially negative oxygen directed inward, and surrounding anions with partially positive hydrogens directed inwards.


CHM 101 - Reeves


Strong e lectro lyte

++

--

-

++

++

-

-

-

-++

C a 2+ C l-

W eak e lectro lyte

+

+

-

-

H + F -H F

N onelectro lyte

O 2


CHM 101 - Reeves


When aqueous silver nitrate (AgNO3)is added to aqueous sodium chloride (NaCl), a white solid forms. This precipitate is silver chloride (AgCl)


CHM 101 - Reeves

CHM 101 – Chapter FourThe solubility rules provide guidelines for deciding which

compounds are soluble and which are insoluble


CHM 101 - Reeves

CHM 101 – Chapter FourThe solubility rules provide guidelines for deciding which

compounds are soluble and which are insoluble

Generally, you need to know that the following ionic compounds are soluble:

Use these rules and/or the Solubility Table to predict the results of a metathesis reaction.


CHM 101 - Reeves

CHM 101 – Chapter FourMetathesis Reactions

Reactions in which cations and anions appear to exchange partners.

When aqueous lead (II) acetate is mixed with aqueous sodium chloride, a metathesis reaction occurs, forming an insoluble precipitate.

A more accurate way to depict this reaction is to list the species actually present in aqueous solution, the ions themselves

produces the net ionic equation


CHM 101 - Reeves

CHM 101 – Chapter FourAcids are substances that produce

hydrogen ions (H+) when dissolved in water. • Because a hydrogen atom consists of one proton and one electron, a hydrogen ion is a proton.• Thus, acids are often defined as proton donors• There are seven common strong acids (Table 4.2) that must be memorized.

Bases are substances that consume hydrogen ions (H+) when dissolved in water.

• Bases often produce hydroxide ion when they dissolve in water. • The most common strong bases are the metal hydroxides (eg. NaOH, Ca(OH)2, Al(OH)3, etc.)


CHM 101 - Reeves


Strong acid /base

--

-

-

-

-

-

+

C l-

+

+

++

+

+

H +

hydrochloric acid (H C l)

Strong acids/bases are strong electrolytes that dissociate completely.

Weak acids/bases are weak electrolytes that dissociate only slightly. W eak acid/base

+

-

-

H + F -H F

+

hydroflouric acid (H F)


CHM 101 - Reeves

CHM 101 – Chapter FourAcid/Base Reactions

Reactions between strong acids and bases are similar to metathesis rxns. One of the products is water.

Consider the reaction of sulfuric acid with potassium hydroxide.

Again the most accurate way to describe this reaction is by considering the ions themselves

produces the net ionic equation


CHM 101 - Reeves

CHM 101 – Chapter FourConcentration of Solutions

Suppose 1.0 moles of hydrochloric acid is dissolved in 500 ml of water.

0.1 moles H+

0.1 moles Cl-

We define the Molarity (M) of solute A in a solution assolutionofliter

AofmolesM A


CHM 101 - Reeves


200 mL

0.1 moles H+

0.1 moles Cl-

Suppose 200 mL were removed and placed in a separate flask.

HClClHMMM


CHM 101 - Reeves

CHM 101 – Chapter FourSolution Concentrations

The concentration of a solution is independent of the amount (intensive property) and can be used to convert between volume and moles.

How many moles of HCl are in 50 mL of a 2.0 M solution?

What volume of this solution would provide 0.36 moles of HCl?


CHM 101 - Reeves

CHM 101 – Chapter FourIf 25 mL of a 1.0 M solution of copper II sulfate is transferred to a 250 mL volumetric flask and the solution is diluted to volume with water, what is the concentration of the new solution?

Moles of CuSO4:

Molarity of soln:


CHM 101 - Reeves

CHM 101 – Chapter FourWhat volume of 0.56 M sulfuric acid solution must be mixed

with sufficient water to create 325 mL of 0.15 M sulfuric acid?

Moles of H2SO4:

Volume of soln:

What volume of this new sulfuric acid solution is needed to completely react 2.56 g of potassium hydroxide?


CHM 101 - Reeves

CHM 101 – Chapter Four Supplement:Measuring Acidity: The pH Scale

• In aqueous solution, the concentration of hydrogen ions [H+] typically ranges form 1.0 M to 1x10-14M

• To provide a convenient way to describe acidity, the pH scale was defined:

• Because the scale involves a minus sign, acidic solutions, with high hydrogen ion concentrations, have low pH.

• Thus, the pH of a solution for which [H+] = 0.001 M is

department of chemistry and biochemistry chm 101 - reeves chm 101 – chapter four properties of...

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