SOLUTIONS, ACIDS AND

BASESChapter 8

FORMATION OF SOLUTIONS

For a solution to form, one substance must dissolve in another.

Even though we usually think of a solid dissolving in a liquid, any state of matter can become part of a solution.

Scuba divers breathe with the aide of compressed air(78% nitrogen). As a diver descends (the deeper the diver goes), the greater is the pressure of the air in the diver’s lungs and the more nitrogen dissolves in the blood and tissues of the body. If divers surface too quickly, the nitrogen that has dissolved in the blood and tissues can bubble out of the solution and become trapped in joints causing great pain (“the bends”).

A QUICK REVIEW OF SOLUTIONS A solution is a homogeneous mixture of two or

more substances.

Every solution has two types of components: a solute (salt) and a solvent(water).

For a solute to dissolve in water, the solute and solvent particles must attract one another.

Solutes and solvents can be solids, liquids or gases.

DISSOLVINGSubstances can dissolve in water three ways:

Dissociation of Ionic Compounds: sodium chloride crystal and water

Dispersion of Molecular Compounds: hard candy and saliva

Ionization of Molecular Compounds: HCl and water

The process in which neutral molecules gain or lose electrons is known as ionization.

PROPERTIES OF LIQUID SOLUTIONS Three physical properties of a solution that can differ

from those of its solute and solvent are as follows: Conductivity

Sodium chloride dissociates in water Hydrogen chloride ionizes in water

Freezing point Magnesium chloride dissociates and interferes with the freezing

process changing it from 0ºC to as low as -15ºC

Boiling point Ethylene glycol and water (coolant in most car radiators) raises the

boiling point of water from 100ºC to prevent overheating

HEAT OF SOLUTION During the formation of a solution, energy is either released

or absorbed.

Sodium hydroxide dissolves in water and becomes warmer (exothermic: releasing energy to the surroundings)

Ammonium nitrate , used in cold packs, dissolves in water and becomes colder (endothermic: absorbing energy from the surroundings)

In order for a solution to form, both the attractions among solute particles and the attractions among solvent particles must be broken. Breaking of attractions requires energy.

As the solute dissolves, new attractions form and the formation of attractions releases energy. The is the difference between these energies.

heat of solution

FACTORS AFFECTING RATES OF DISSOLVING Factors that affect the rate of dissolving

include surface area, stirring and temperature.The more frequent the collisions between the

solute and solvent, the faster rate of dissolving.

SOLUBILITY AND CONCENTRATION

Lemonade, Iced tea, and hot tea can all “hold” different concentrations of sugar.

They each have different factors for solubility of sugar.

SOLUBILITY The maximum amount of a solute that

dissolves in a given amount of solvent at a constant temperature is called solubility.

Grams of solute per 100 grams of solvent at a specified temperature

Knowing the solubility of a substance can help you classify solutions based on how much solute they contain.

Solutions are described as saturated(solvent filled with solute), unsaturated(solvent does not fill the solute) or supersaturated(more solute than the solution can hold), depending on the amount of solute in solution at a given temperature.

FACTORS AFFECTING SOLUBILITY

Three factors affect the solubility of a solute.Polar and Nonpolar Solvents – oil is soluble in

soapy water -“like dissolves

like”

Temperature – generally, solubility increases as the temperature increases (iced tea versus hot tea with sugar)

Pressure – 12-ounce can of soda/carbonation (CO2) dissolved in a liquid

CONCENTRATION OF SOLUTIONSConcentration can be expressed as percent in three ways.

Percent by Volume

Percent by Mass

Molarity

PROPERTIES OF ACIDS AND BASES

Sodium hydroxide (a base) is added to a mixture of animal/vegetable fats and boiled until the sodium hydroxide reacts with the fats producing glycerol and soap. After glycerol is separated from the soap, the soap is purified and other chemicals are mixed in for color and scent.

IDENTIFYING ACIDSAn acid is a compound that produces hydronium ions when dissolved in water.Some general properties of acids include sour taste, reactivity with metals, and ability to produce color changes in indicators.

Sour Taste: lemons, grapefruits, limes, and oranges (citric acid) vinegar (acetic acid)Reactivity With Metals: aluminum foil over spaghetti sauce (citric acid) –

a single replacement reactionColor Changes in Indicators: litmus paper (a common indicator) turns red in the presence of an acid

IDENTIFYING BASESA base is a compound that produces hydroxide ions when dissolved in water. Some general properties of bases include bitter taste, slippery feel, and ability to produce color changes in indicators.

Bitter Taste: unsweetened chocolate, many cough syrupsSlippery Feel: wet soap, some wet rocksColor Changes in Indicators: bases turn litmus paper blue

OTHER INDICATORSPhenolphthalein:

In a basic solution, is redIn an acidic solution, is colorless

Natural indicators: flowers, like hydrangeas

In basic soil, flowers are pinkIn acidic soil, flowers are blue

NEUTRALIZATION AND SALTSThe reaction between an acid and a base is called neutralization.

FISH – BASE LEMON – ACID REACTION MAKES FISH TASTE LESS BITTER

This reaction is called neutralization.

The neutralization reaction between an acid and a base produces a salt and water.

STRENGTH OF ACIDS AND BASES

Certain compounds of chlorine are dissolved in swimming pool water to prevent the growth of bacteria.

The concentration of hydronium ions in solutions must be carefully controlled.

Determining the concentration of hydronium or hydroxide ions is one way to determine the acidity or basicity of a solution.

THE PH SCALE Chemists use a number scale from 0 to 14 to

describe the concentration of hydronium ions in a solution.

The PH of a solution is a measure of its hydronium ion concentration. 7 is neutral Acids have a pH less than 7 Bases have a pH greater than 7

The lower the pH value, the greater the H3O+ ion concentration in solution is. The higher the pH value, the lower the H3O+.

STRONG ACIDS AND BASES

To review… Some reactions go to completion while other reach equilibrium

When certain acids and bases dissolve in water, the formation of ions from the solute almost goes to completion. These acids and bases are classified as strong.

Strong Acids When strong acid dissolve in water, they ionize almost

completely. Examples: sulfuric acid and nitric acid

Strong Bases Strong bases dissociate almost completely in water. Examples: calcium hydroxide and potassium hydroxide

WEAK ACIDS AND BASESWeak acids and bases ionize or dissociate only slightly in water.

Weak Acids Citric acid in orange juice, acetic acid in vinegar Equilibrium favors the reactants over the products so few ions form

in solution Have a higher pH

Weak Bases Toothpaste and shampoo contain weak bases Ammonia (colorless gas with distinctive smell)

Buffers A solution that is resistant to large change in pH Prepared by mixing a weak acid and its salt or a weak bases and its

salt pH is relatively constant

ELECTROLYTES Sports drinks taste salty because they contain salts

of elements; they help restore the balance of ions in your body.

Electrolytes ionize or dissociate into ions when they dissolve in water and results in a solution that can conduct an electric current.

Strong acids and bases are strong electrolytes because they dissociate or ionize almost completely in water.

Batteries and fuel cells also produce electricity and contain electrolytes.

RIVER OF LIFEClass Participation Opportunity:Write a research paper that includes the following concepts:

1. compounds in blood2. blood flow through the

body3. maintaining blood’s pH4. scientists who have

contributed to our understanding of bloodYour paper should include information found on pages 250-253. It should also contain information from two other sources.

FORMAL LAB REPORT: YOUR WAYPossible investigative questions:

Determining Solubility1. How can you determine the solubility of a

substance in water?Comparing Solubilities and Rates of Dissolving2. How does surface area affect the rate of dissolving

and solubility?3. How does temperature affect the rate of dissolving

and solubility?Testing Antacids4. Which antacid neutralizes stomach acid with the

smallest number of drops?Comparing Antacids5. Which brand of antacid neutralizes the most acid

per dose?