CHAPTER 8Solutions, Acids, and Bases

8.1 Formation of Solutions

Dissolving Recall that a solution is a homogeneous

mixture of two or more substances Every solution has two components:

Solute Substance whose particles are dissolved in a

solution Solvent

Substance in which the solute dissolves Ex. Seawater – water is solvent, salt is solute

Dissolving Solutes and solvents can take the form

of solid, liquid, or gas Solution takes state of solvent

Substances can dissolve in water in three ways Dissociation Dispersion Ionization

Dissociation of Ionic Compounds For a solute to dissolve in water

The solute and solvent particles must attract to one another The solute particles are attracted and the

solvent particles are attracted to one another So, before a solution can form, those

attractions must be overcome Process in which an ionic compound

seperates into ions as it dissolves is called dissociation

Dispersion of Molecular Compounds

The water in your saliva dissolves the sugar and flavoring in candy throughout your mouth Sugar dissolves in water by dispersion, or

breaking into small pieces that spread throughout the water Both sugar and water are polar, therefore

attract When enough water molcules have surrounded

the sugar molecule, sugar molecule breaks free and is pulled into solution

Ionization of Molecular Compounds

HCl – molecular compound where hydrogen and chloride share an electron When HCl gas dissolves in water, the H

molecule is transferred to water H30+ and Cl- are produced

When a neutral molecule gain or lose electrons it is known as ionization

This is a chemical change Unlike dispersion and dissociation

Properties of Liquid Solutions Three physical properties of a solution

that can differ from those of its solute and solvent are: Conductivity Freezing point Boiling point

Conductivity Solid sodium chloride is a poor conductor

When it dissociates in water, the sodium and chloride ions are able to move freely They will then conduct electricity

Freezing Point and Boiling Point MgCl2 is what is sometimes spread on

icy roads When it dissolves in melting ice, it

dissociates into Mg2+ and Cl- These ions are able to interfer with freezing

process Salted roads have a freezing point of -15°C

Freezing Point and Boiling Point Solute can also raise boiling point

ex. Coolant used in most car radiators Adding ethylene glycol to water raises the

boiling point Solution helps prevent the engine from

overheating Also prevents the the liquid from freezing in the

winter

Heat of Solution During the formation of a solution,

energy is either released or absorbed Can be described as either exothermic or

endothermic Dissolving sodium hydroxide in water is

exothermic, releases heat How it Works box explains how cold packs are

used

Heat of Solution In order for a solution to form, all

attractions must be broken That requires energy Formation of solutions, releases energy

The difference between these energies is called the heat of solution

Factors Affecting Rates of Dissolving

Reates of dissolving depend on the frequency and energy of collisions Formation of solutions, collisions occur

between solute and solvent particles Factors that affect the rate of dissolving

include: Surface area Stirring temperature

Factors Affecting Rates of Dissolving

The greater the surface area of a solid solute, the more requent the collision are between the solute and the solvent particles Increase surface area by breaking into

smaller pieces

Stirring Moves dissolved particles away from

surface Allows more collisions between solute and

solvent

Factors Affecting Rates of Dissolving

Increasing temperature is another way to speed up dissolving Increase in temperature causes the

particles to move faster Both the number of collisions and the

energy of these collisions increases Goes into solution more quickly

Review Quiz 1. What do we call the substance whose

particles are dissolved in a solution? 2. What do we can the substance the

dissolves the particles in a solution? 3. When a neutral molecule gains or

loses electrons, it is called ________? 4. List two of the three factors that

affect the rate of dissolving?

8.2 Solubility and Concentration

Solubility Solubility

The max amount of a solute that dissolves in a given amount of solvent at a constant temperature Usually expressed in grams of solute in 100g of

solvent

Solutions are described as: Saturated Unsaturated Supersaturated

Solubility Saturated

Sugar is very soluble in water At 20 degrees C you can dissolve 203.9

grams of sugar in 100g of water What will happen if you try to dissolve more

than that? The extra sugar will not go into solution

The solution is already saturated One that contains as much solute as the solvent

can hold at a given temperature

Solubility Unsaturated

A solution that has less than the max amount of solute that can be dissolved many beverages are unsaturated

Solubility Supersaturated

If you heat a solvent above the average temperature it can dissolve more solute If you then carefully cool the solvent back to the

average without jarring it, you may be able to keep the extra solute in the solution

Supersaturated solution One that contains more solute than it can normally

hold at a given temperature Very unstable If a tiny particle falls into a supersaturated solution,

the extra solute may rapidly fall out

Factors Affecting Solubility Have you ever tried to wash oil or grease

off your hands? Will not come off in just water, but in soapy

water it will wash off Not soluble in water, but in soapy water it is

Three factors that affect solubility: Polarity of the solvent Temperature pressure

Factors Affecting Solubility Polar and Nonpolar Solvents

Oil molecules are nonpolar, water is polar Common guideline for predicting solubility is

‘like dissolves like’ More likely to dissolve if solute and solvent

are both polar or both nonpolar Soap molecules have a polar and non polar end Makes it easy to dissolve oil

Factors Affecting Solubility Temperature

In general the solubility of a solute increases when you increase the temperature of the solvent

When water temp increases, bubbles start to come out of the water These are gas bubbles that are dissolved in

water Unlike most solids, gases usually become less

soluble as the temperature of solvent increases

Factors Affecting Solubility Pressure

Incresing the pressure on a gas increases its solubility in a liquid

Pressure of carbon dioxide in a 12 oz can of soda at room temp can by two to three times atmospheric pressure

Concentration of Solutions Concentration

The amount of solute dissolved ina specified amount of solution

Can be expressed as: percent by volume percent by mass molarity

Percent by Volume Often times on fruit juice bottles have a

percentage of real fruit juice in it. Ex. 27% real fruit juice

To calculate the concentration as a percent by volume: Page 238

Percent by Mass

8.3 Properties of Acids and Bases

Identifying Acids Acid

Compound that produces hydronium ions (H3O+) when dissolved in water.

Acids have certain chemical and physical properties that are similar Sour taste Reactivity with metals Ability to produce color changes in indicators

Sour Taste Foods that taste sour often contain acids

Lemons, grapefruits, limes, and oranges all contain citric acid

Dairy products that have spoiled contain butyric acid

NEVER TEST AN ACID BY TASTING IT!

Reactivity with Metals Sometimes when you cover food with

aluminum foil, it gets small holes in it, or the food starts to taste metallic Foods with tomatoes contain citric acid

which will react with aluminum (metal) Single replacement reaction

Color Changes in Indicators Indicator

Any substance that changes color in the presence of an acid or base Common idicator is litmus

Dye derived from plants called lichens Blue litmus paper turns red in the presence

of acid

Identifying Bases Base

A compound that produces hydroxide ions when dissolved in water

Have certain physical and chemical properties in common Bitter taste Slippery feel Ability to produce color changes in indicators

Do not react with metals (usually) Zinc and aluminum react vigorously with

sodium hydroxide

Bitter Taste Have you ever tasted unsweetened

chocolate? Sometimes called baking chocolate… Coco beans contain a base called

theobromine that gives unsweetened chocolate its bitter taste

Cough syrups and other liquid medicines contain similar bases Fruit flavorings are added to mask the bitter

taste

Slippery Feel Wet soap and many cleaning supplies

are slippery because they contain bases When wet, some rocks feel slippery

Water dissolves compounds trapped in the rocks, producing basic solution

Color Changes in Indicators Bases turn red litmus paper blue.

Will change back to red if you put acid on the paper

Phenolphthalein is another example of an acid-base indicator In solution containing base, solution is red In solution containing an acid, colorless

Hydrangeas contain natural indicators Color depends on acid/base soil

Acid soil – bluish-purple Basic soil - pink

Neutralization and Salts Sometimes people squeeze lemon juice

over fish Fish is basic and can sometimes taste bitter Lemon juice contains acids, makes it taste

less bitter Reaction between acid and base is called

neutralization Negative ions in acid combine with positive

ions in base to form a salt Hydronium ions combine with hydroxide

ions to form water

Proton Donors and Acceptors Acids lose, or ‘donate’ protons Bases accept, forming water, a neutral

molecule Water can act as either an acid or a base

depending on what it is reacting with

8.4 Strength of Acids and Bases

The pH Scale Chemists use a scale from 0-14 to

describe the concentration of hydronium ions in a solution pH – measure of hydronium ion

concentration 7 indicates a neutral solution Bases are greater than 7 Acids are less than 7

Lower the pH value, the higher the concentration of H30+

Strong Acids HCl is an example of a strong acid

When dissolved in water, there are about the same number of hydronium ions as there were molecules of HCl

When strong acids dissolve in water, they ionize almost completely Other strong acids are sulfuric acid, and

nitric acid

Strong Bases Strong bases dissociate almost

completely in water. Sodium hydroxide dissociates into sodium

and hydroxide ions Other strong bases are calcium hydroxide and

potassium hydroxide

Weak Acids and Bases Weak acids and bases ionize or

dissociate only slightly in water It is important to know the difference

between concentration and strength Concentration: amount of solute dissolved

in a given amout of solution Strength: solute’s tendency to form ions in

water Buffers: solution that is resistant to large

changes in pH

Electrolytes Electrolyte

Substance that ionizes or dissociates into ions when it dissolves in water Resulting solution can conduct electricity Sports drinks help restore the ions in your body

Strong acids/bases are strong electrolytes Batteries contain electrolytes