Homogeneous Homogeneous Aqueous SystemsAqueous Systems

Dr. YagerDr. YagerPrentice-Hall Chapter 15.2Prentice-Hall Chapter 15.2

ObjectivesObjectives

IdentifyIdentify the difference between a solute and the difference between a solute and a solvent.a solvent.

ExplainExplain why all ionic compounds are why all ionic compounds are electrolytes in solution.electrolytes in solution.

ExplainExplain how to write a formula for a hydrate. how to write a formula for a hydrate.

Homogeneous Aqueous SystemsHomogeneous Aqueous Systems

An ordinary dill pickle An ordinary dill pickle from the deli can be a from the deli can be a source of light! Iron or source of light! Iron or copper electrodes are copper electrodes are inserted into the ends of inserted into the ends of the pickle and the pickle and connected to a source connected to a source of alternating electric of alternating electric current. You will learn current. You will learn what kind of solution what kind of solution conducts electricity.conducts electricity.

Solvent and SoluteSolvent and Solute

An An aqueous solutionaqueous solution is water that is water that contains dissolved substances.contains dissolved substances.

In a solution, the dissolving medium In a solution, the dissolving medium is the is the solventsolvent..

In a solution, the dissolved particles In a solution, the dissolved particles are the are the solutesolute..

Solvent and Solute (cont)Solvent and Solute (cont)

A solvent dissolves the solute. The solute A solvent dissolves the solute. The solute becomes dispersed in the solvent.becomes dispersed in the solvent.

Solvents and solutes may be gases, Solvents and solutes may be gases, liquids, or solids.liquids, or solids.

Solute particles can be atoms, ions, or Solute particles can be atoms, ions, or molecules.molecules.

FiltrationFiltration

If you filter a solution through filter paper, both the If you filter a solution through filter paper, both the solute and the solvent pass through the filter.solute and the solvent pass through the filter.

What Happens?What Happens?

As individual solute ions break away from the As individual solute ions break away from the crystal, the negatively and positively charged crystal, the negatively and positively charged ions become surrounded by solvent molecules, ions become surrounded by solvent molecules, and the ionic crystal dissolves.and the ionic crystal dissolves.

The process by which the positive and negative The process by which the positive and negative ions of an ionic solid become surrounded by ions of an ionic solid become surrounded by solvent molecules is called solvent molecules is called solvationsolvation..

Solvation of an Ionic SolidSolvation of an Ionic Solid

Polar vs Nonpolar SolventsPolar vs Nonpolar Solvents

Polar solventsPolar solvents such as water dissolve such as water dissolve ionic compounds and polar ionic compounds and polar compounds. compounds.

Nonpolar solventsNonpolar solvents such as gasoline such as gasoline dissolve nonpolar compounds.dissolve nonpolar compounds.

Oil and water do not mix.Oil and water do not mix.

Electrolytes & NonelectrolytesElectrolytes & Nonelectrolytes

An An electrolyteelectrolyte is a compound that conducts an is a compound that conducts an electric current when it is in an aqueous solution electric current when it is in an aqueous solution or in the molten state. or in the molten state.

All ionic compounds are electrolytes because All ionic compounds are electrolytes because they dissociate into ions.they dissociate into ions.

The bright glow shows The bright glow shows that sodium chloride is that sodium chloride is a a strong electrolytestrong electrolyte because nearly all the because nearly all the dissolved sodium dissolved sodium chloride exists as chloride exists as separate Naseparate Na++ and Cl and Cl–– ions.ions.

A A weak electrolyteweak electrolyte conducts electricity conducts electricity poorly because only poorly because only a fraction of the a fraction of the solute in the solution solute in the solution exists as ions.exists as ions.

A compound that does A compound that does not conduct an electric not conduct an electric current in either aqueous current in either aqueous solution or the molten solution or the molten state is called a state is called a nonelectrolytenonelectrolyte. .

HydratesHydrates Some compounds naturally contain water Some compounds naturally contain water

molecules that are embedded in their crystal molecules that are embedded in their crystal structure, called structure, called water of hydrationwater of hydration..

A compound that contains water of hydration is A compound that contains water of hydration is called a called a hydratehydrate..

In writing the formula of a hydrate, use a dot to In writing the formula of a hydrate, use a dot to connect the formula of the compound and the connect the formula of the compound and the number of water molecules per formula unit.number of water molecules per formula unit.

Hydrates (cont)Hydrates (cont)

The forces holding water molecules in a hydrate The forces holding water molecules in a hydrate are not very strong, making the water relatively are not very strong, making the water relatively easy to remove through heating.easy to remove through heating.

A compound that contains A compound that contains nono water of hydration water of hydration is called an is called an anhydrateanhydrate..

The process of removing water from a compound The process of removing water from a compound is called is called dehydrationdehydration..

A sample of blue CuSOA sample of blue CuSO44·5H·5H22O is heated.O is heated.

Blue crystals of CuSOBlue crystals of CuSO44·5H·5H22O crumble to a white O crumble to a white

anhydrous powder that has the formula CuSOanhydrous powder that has the formula CuSO44..

Efflorescent HydratesEfflorescent Hydrates

If a hydrate has a vapor pressure higher than the If a hydrate has a vapor pressure higher than the pressure of water vapor in the air, the hydrate pressure of water vapor in the air, the hydrate will lose its water of hydration, or will lose its water of hydration, or effloresceeffloresce..

Hydroscopic HydratesHydroscopic Hydrates

Hydrated salts that have a low vapor pressure Hydrated salts that have a low vapor pressure remove water from moist air to form higher remove water from moist air to form higher hydrates. These hydrates and other hydrates. These hydrates and other compounds that remove moisture from air are compounds that remove moisture from air are called called hydroscopichydroscopic..

When treated paper is exposed to moist air, it When treated paper is exposed to moist air, it turns pink because of the formation of the hydrate turns pink because of the formation of the hydrate cobalt(II) chloride hexahydrate (CoClcobalt(II) chloride hexahydrate (CoCl22·6H·6H22O).O).

Percent Water CalculationPercent Water Calculation

To determine what percent of a hydrate is water, To determine what percent of a hydrate is water, first determine the mass of the number of moles first determine the mass of the number of moles of water in one mole of hydrate. Then determine of water in one mole of hydrate. Then determine the total mass of the hydrate. The percent mass the total mass of the hydrate. The percent mass of water can be calculated as:of water can be calculated as:

Practice ProblemPractice Problem

Deliquescent HydratesDeliquescent Hydrates

Deliquescent compoundsDeliquescent compounds remove sufficient remove sufficient water from the air to dissolve completely and water from the air to dissolve completely and form solutions. These compounds become wet form solutions. These compounds become wet when exposed to normally moist air.when exposed to normally moist air.

The deliquescent substance, sodium The deliquescent substance, sodium hydroxide, absorbs moisture from air.hydroxide, absorbs moisture from air.

A solution forms.A solution forms.

1. Choose the correct words for the spaces. 1. Choose the correct words for the spaces. In any solution, the material that is In any solution, the material that is dissolved is called the _________ and the dissolved is called the _________ and the material in which the substance is material in which the substance is dissolved is called the _________.dissolved is called the _________.

a.a. solid, liquidsolid, liquid

b.b. solvent, solute solvent, solute

c.c. solute, solventsolute, solvent

d.d. crystal, dispersercrystal, disperser

1. Choose the correct words for the spaces. 1. Choose the correct words for the spaces. In any solution, the material that is In any solution, the material that is dissolved is called the _________ and the dissolved is called the _________ and the material in which the substance is material in which the substance is dissolved is called the _________.dissolved is called the _________.

a.a. solid, liquidsolid, liquid

b.b. solvent, solute solvent, solute

c.c. solute, solventsolute, solvent

d.d. crystal, dispersercrystal, disperser

2.2. In the solution process, theIn the solution process, the

a.a. solvent molecules become dispersed in an solvent molecules become dispersed in an

ionic crystal.ionic crystal.

b.b. solvent molecules are surrounded by solvent molecules are surrounded by

positive and negative ions.positive and negative ions.

c.c. ions become emulsified in the solventions become emulsified in the solvent

d.d. positive and negative ions are surrounded positive and negative ions are surrounded

by solvent molecules.by solvent molecules.

2.2. In the solution process, theIn the solution process, the

a.a. solvent molecules become dispersed in an solvent molecules become dispersed in an

ionic crystal.ionic crystal.

b.b. solvent molecules are surrounded by solvent molecules are surrounded by

positive and negative ions.positive and negative ions.

c.c. ions become emulsified in the solventions become emulsified in the solvent

d.d. positive and negative ions are surrounded positive and negative ions are surrounded

by solvent molecules.by solvent molecules.

3.3. All ionic compounds are electrolytes All ionic compounds are electrolytes because theybecause they

a.a. conduct electricity in the solid state. conduct electricity in the solid state.

b.b. dissociate into ions in the aqueous and/or dissociate into ions in the aqueous and/or molten state.molten state.

c.c. remain as positive-negative pairs even remain as positive-negative pairs even when dissolved. when dissolved.

d.d. only conduct electricity in the molten state. only conduct electricity in the molten state.

3. All ionic compounds are electrolytes 3. All ionic compounds are electrolytes because theybecause they

a.a. conduct electricity in the solid state. conduct electricity in the solid state.

b.b. dissociate into ions in the aqueous and/or dissociate into ions in the aqueous and/or molten state.molten state.

c.c. remain as positive-negative pairs even remain as positive-negative pairs even when dissolved. when dissolved.

d.d. only conduct electricity in the molten state. only conduct electricity in the molten state.

4. The formula for iron(II) sulfate 4. The formula for iron(II) sulfate heptahydrate isheptahydrate is

a.a. FeSOFeSO44(H(H22O)O)77

b.b. FeSOFeSO44•(H•(H22O)O)77

c.c. Fe•2SOFe•2SO44•7H•7H22OO

d.d. FeSOFeSO44•7H•7H22OO

4. The formula for iron(II) sulfate 4. The formula for iron(II) sulfate heptahydrate isheptahydrate is

a.a. FeSOFeSO44(H(H22O)O)77

b.b. FeSOFeSO44•(H•(H22O)O)77

c.c. Fe•2SOFe•2SO44•7H•7H22OO

d.d. FeSOFeSO44•7H•7H22OO