SolutionsChapter 7

Section 1 Solutions and Other Mixtures

Section 2 How Substances Dissolve

Section 3 Solubility and Concentration

• Skills• Physical and chemical properties

• Physical and chemical changes

• States of matter

• Functional relationships

• Conversion factors

• Atomic Structure

• Molar Mass

• Chemical formulas

• Determining empirical and molecular formulas

• Naming ionic, covalent, and organic compounds

• Classifying reaction types

• Balancing chemical reactions

• Determining mole and mass fractions

• Concentrations

Section 1 Solutions andOther MixturesObjectives

• Distinguish between heterogeneous mixturesand homogeneous mixtures.

• Compare the properties of suspensions,colloids, and solutions.

• Give examples of solutions that contain solidsor gases.

Heterogeneous Mixtures

• The amount of each substance in differentsamples of a heterogeneous mixture varies.

• A suspension is a mixture in which largeparticles of a material are more or less evenlydispersed throughout a liquid or gas.• Example: natural orange juice, which contains

particles of pulp.

• Particles in a suspension may settle overtime, and may be filtered out.

Suspension

Heterogeneous Mixtures, continued

• Some combinations of liquids will not mix,but will separate spontaneously.• Example: Oil and vinegar in salad dressing

separates into two layers.

• Liquids that do not mix with each other areimmiscible.

• One way to separate two immiscible liquidsis to carefully pour the less dense liquid offthe top. This is called decanting.

Comparing Miscible and ImmiscibleLiquids

Chapter 7

Heterogeneous Mixtures, continued

• A colloid is a mixture consisting of tinyparticles that are intermediate in size betweenthose in solutions and those in suspensionsand that are suspended in a liquid, solid orgas.

• Particles in a colloid are too small to settle out.

• However, particles in a colloid are largeenough to scatter light that passes through:this is called the Tyndall effect.

Colloids

Heterogeneous Mixtures, continued

• Examples of familiar materials that arecolloids include gelatin desserts, egg whites,and blood plasma.

• Some immiscible liquids can form colloids.

• An emulsion is any mixture of two or moreimmiscible liquids in which one liquid isdispersed in the other.

Emulsions

Homogeneous Mixtures

• Homogeneous mixtures not only lookuniform, but are uniform.• Example: salt water, which looks uniform even when

you examine it under a microscope

• A solution is a homogeneous mixture oftwo or more substances uniformlydispersed throughout a single phase.• In a solution, the solute is the substance that

dissolves in the solvent.

• The solvent is the substance in which the solutedissolves.

Homogeneous Mixture

Solutions

Chapter 7Solutes, Solvents, and Solutions

Homogeneous Mixtures, continued

• Miscible liquids mix to form solutions.

• One way to separate miscible liquids is bydistillation, which works when the twomiscible liquids have different boiling points.

• Fuels such as gasoline, diesel fuel, andkerosene are made from a liquid solutioncalled petroleum, also called crude oil.• Components of crude oil are separated by

fractional distillation.

Chapter 7Fractional Distillation in Refineries

Homogeneous Mixtures, continued

• Other states of matter can also formsolutions.

• The air you breathe is a solution of nitrogen,oxygen, argon, and other gases.

• The liquid element mercury dissolves in solidsilver to form a solution called an amalgam,which can be used to fill cavities in teeth.

• An alloy is a solid or liquid mixture of two ormore metals.

Section 2 How SubstancesDissolveObjectives

• Explain how the polarity of water enables it todissolve many different substances.

• Relate the ability of a solvent to dissolve asolute to the relative strengths of forces betweenmolecules.

• Describe three ways to increase the rate atwhich a solute dissolves in a solvent.

• Explain how a solute affects the freezing pointand boiling point of a solution.

Water: A Common Solvent

• Many different substances can dissolve inwater. For this reason, water is sometimescalled the universal solvent.

• Water can dissolve ionic compounds becauseof its structure: it is a polar compound,which is a molecule that has an unevendistribution of electrons.

• Because they are polar, water moleculesattract both the positive and negative ions ofan ionic compound.

Water: A Common Solvent,continued

• Polar water molecules pull ionic crystalsapart, as shown below.

• The partially negative oxygen atoms of watermolecules attract the positively charged sodium ions.

• The partially positive hydrogen atoms of watermolecules attract the negatively charged chloride ions.

Water: A Common Solvent,continued

• Water exhibits hydrogen bonding: theintermolecular force occurring when a hydrogenatom that is bonded to a highly electronegativeatom of one molecule is attracted to twounshared electrons of another molecule.

• Hydrogen bonding determines many of water’sunique properties.

• Hydrogen bonding enables water to dissolvemany molecular compounds, such as sugar.

Hydrogen Bonding

Water: A Common Solvent,continued

• A rule of thumb in chemistry is that like dissolveslike.

• A nonpolar compound is a compound whoseelectrons are equally distributed among itsatoms.

• A nonpolar compound usually will not dissolve inwater, because its intermolecular forces do notmatch with those of water.

Like Dissolves Like

The Dissolving Process

• According to the kinetic theory of matter, watermolecules in a glass of tea are always moving.

• When sugar is poured into the tea, watermolecules collide with sugar molecules.

• Sugar molecules form a solution with watermolecules at the surface of the sugar crystals.

• As layers of sugar molecules leave the crystal,more layers are uncovered and dissolve amongthe solvent (water) molecules in the same way.

Dissolving Process

The Dissolving Process, continued

• Solutes with a larger surface area dissolvefaster.• More solute particles are exposed to the solvent.

• Stirring or shaking a solution helps the solutedissolve faster.• Dissolved solute particles diffuse throughout the

solution faster, allowing more solute particles todissolve.

• Solutes dissolve faster when the solvent is hot.• Collisions occur between solute and solvent

particles more frequently and with more energy.

Surface Area

Chapter 7Factors Affecting the Rate ofDissolution

The Dissolving Process, continued

• Solutes affect the physical properties of asolution.• Examples:

• If you dissolve salt in water, it will boil at ahigher temperature and freeze at a lowertemperature.

• The coolant mixture ofethylene glycol (antifreeze)with water keeps a car’sradiator fluid from freezing inwinter or boiling in summer.

Section 3 Solubility andConcentrationObjectives

• Explain the meaning of solubility and compare thesolubilities of various substances.

• Describe dilute, concentrated, saturated, andsupersaturated solutions.

• Relate changes in temperature and pressure tochanges in solubility of solid and gaseous solutes.

• Express the concentration of a solution asmolarity, and calculate the molarity of a solutiongiven the amount of solute and the volume of thesolution.

Solubility in Water

• Solubility is the maximum amount of a solutethat will dissolve in a given quantity of solventat a given temperature and pressure.• Some substances, such as oil, are insoluble in

water, meaning they never dissolve.• Other substances are said to be soluble in

water because they dissolve easily in water.• However, there is often a limit to how much of a

substance will dissolve.

• Different substances have differentsolubilities.

Chapter 7Solubility of a Solid in a Liquid

Solubility in Water, continued

• Concentration is the amount of a particularsubstance in a given volume of solution.

• A solution whose ratio of solute to solvent isrelatively high is referred to as concentrated.

• A solution whose ratio of solute to solvent isrelatively low is referred to dilute.

Chapter 7Concentration

Solubility in Water, continued

• An unsaturated solution contains less thanthe maximum amount of solute that candissolve.

• A saturated solution is at a point where nomore solute can be dissolved under the sameconditions.

• A supersaturated solution holds moredissolved solute than is required to reachequilibrium at a given temperature.

• To make a supersaturated solution, you raise thetemperature of a solution, dissolve more solute, thenlet the solution slowly cool again.

Solubility in Water, continued• Gases can also dissolve in water.

• Unlike solid solutes, gaseous solutes are lesssoluble in warmer water than they are in colderwater.

• The solubility of gases also depends onpressure. Lowered pressure of gas above asolution leads to dissolved gas bubbling out ofthe solution.

• Example: If a scuba diver surfaces too quickly, dissolvednitrogen gas in the bloodstream bubbles out of solution,which causes a painful condition called the bends.

Chapter 7Pressure, Temperature, and Solubilityof Gases

Concentration of Solutions

• The concentration of solutions is expressedas molarity: moles of dissolved solvent perliter of solution.

moles of solute molMolarity = , or

liters of solution LM

• Note that molarity is moles per liter of solution,not per liter of solvent.

• A 1.0 M, “one molar,” solution of NaCl, contains1.0 mol of dissolved NaCl in every 1.0 L ofsolution.

Math Skills

Molarity Calculate the molarity of a sodiumcarbonate, Na2CO3, solution of 38.6 g ofsolute in 0.500 L of solution.

1. List the given and unknown values.Given: mass of sodium carbonate = 38.6 g

volume of solution = 0.500 LUnknown:molarity, amount of Na2CO3 in 1 L

of solution

Math Skills, continued

2. Write the equation for moles Na2CO3 andmolarity.

2 32 3

2 3

mass Na COmoles Na CO =

molar mass Na CO

2 3moles Na COmolarity =

liters of solution

3. Find the number of moles of Na2CO3 andcalculate molarity.

Math Skills, continued

2 3 2 3

38.6 gmoles Na CO = = 0.364 mol Na CO

106 g

2 30.364 mol Na CO

0.500 L solutionmolarity of solution = = 0.728 M

Concentration of Solutions, continued

• Other measures of solution concentrationcan be used.

• These include:• mass percent (grams of solute per 100 g

of solution)• Ingredients in many food and household products

use mass percent.

• parts per million (grams of solute per 106 gof solution)

• Used for very small concentrations, such as forenvironmental regulations.

Practice p.243; Math Skills p. 244

• TERMS TOOLS (equations)

• Density (ρ) (kg/m3, g/cm3)

• Pressure (p) (Pa=N/m3, kPa)

• Mole (mol)

• Molarity (M) (mol/L)

Chapter Review p.214; 1-6, 14-18

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