Solutions, Acids, and Bases

Chapter 8

What Are Acids?• acid - a compound that dissolves in water to

increase the number of hydronium ions, H3O+,

in solution.

• indicator - a compound that can reversibly change color depending on the pH of the solution or other chemical change.– An indicator can tell you whether a substance is

acidic or basic. For example, acids turn blue litmus paper red.

What Are Acids? • An electrolyte is a substance that dissolves in

water to give a solution that conducts an electric current.

• Strong acids ionize completely.• Strong acids are

strong electrolytes.

• Weak acids do not ionize completely.• Weak acids are

weak electrolytes.

• Some examples of strong acids:• Hydrochloric acid, HCl

• present in your stomach• Sulfuric acid, H2SO4

• car batteries; the most-used industrial chemical• Nitric acid, HNO3

• used in manufacturing fertilizers and explosives

• Some examples of weak acids:• Acetic acid, CH3COOH

• the acid in vinegar• Formic acid, HCOOH

• the acid in stinging ants• Citric acid, H3C6H5O7

• the acid in citrus fruits

• base - a compound that dissolves in water to increase the number of hydroxide ions, OH–, in solution.

• Strong bases are ionic compounds that contain a metal ion and a hydroxide ion, for example, NaOH, sodium hydroxide.

• Weak bases, such as ammonia, NH3, ionize incompletely in water to form hydroxide ions.

What is pH

• pH - a value used to express the acidity or basicity of a solution.

• pH values correspond to the concentration of hydronium ions. They also indicate hydroxide ion concentration.• A neutral solution, such as pure water, has a

pH of 7.• An acidic solution has a pH of less than 7.• A basic solution has a pH of greater than 7.

pH Scale

You have learned that acids and bases dissociate into ions in solution. The characteristic ions are the hydronium, or H3O+, ion for acids and the hydroxide, or OH–, ion for bases. Below are listed several reactions between acids and bases.

From what you know about reactions, acids, and bases, predict what the products of the following reactions will be.

1. HCl(aq) + NaOH(aq) ______ + H2O(l)2. HCl(aq) + KOH(aq) KCl(aq) + ______3. HNO3(aq) + KOH(aq) ______ + ______4. H2SO4(aq) + Ca(OH)2(aq) ______ + ______5. HBr(aq) + AgOH(aq) ______ + ______6. HClO4(aq) + NaOH(aq) ______ + ______7. 2HNO3(aq) + Ba(OH)2(aq) ______ + ______8. H2SO4(aq) + 2NH4OH(aq) ______ + ______

• neutralization reaction - reaction between an acid and a base

• Neutralization is an ionic reaction.• Example:– A strong acid such as HCl ionizes completely in

solution:HCl + H2O Cl– + H3O+

– A strong base such as NaOH ionizes completely in solution:

NaOH Na+ + OH–

– The total neutralization reaction is the following:Cl– + H3O+ + Na+ + OH– Na+ + Cl– + 2H2O

• Titration - a neutralization reaction in which the known concentration of one solution is used to determine the unknown concentration of another solution.

• equivalence point - when the amounts of acid and base added are equal

• To a chemist, a salt can be almost any combination of cations and anions.

• Common table salt contains sodium chloride, NaCl, which is a salt that is formed from the reaction of hydrochloric acid with sodium hydroxide.

• Salts are useful substances, and are all around us.– sodium hydrogen carbonate, baking soda– silver bromide and silver iodide, in photographic

film– barium sulfate, sometimes used in taking X rays– calcium carbonate, in chalk, limestone, and

marble

• Soap improves water’s ability to clean because it can dissolve in both oil and in water.• This allows oil and water to form an emulsion

that can be washed away by rinsing.• Soaps are salts of sodium or potassium and

fatty acids.

• Household bleach is a solution of a strong base, sodium hypochlorite (NaOCl).

• Bleach is a strong disinfectant, a chemical substance that kills harmful bacteria or viruses.

• antacid - a weak base that neutralizes stomach acid.– Sodium hydrogen carbonate and magnesium

hydroxide (milk of magnesia) are examples.

• Shampoos are adjusted for an ideal pH.

• Acids keep fruit fresh longer

How can you determine by tasting which foods have a high concentration of one or more acidic compounds?

What property of detergents makes them more useful than soap for washing clothes and dishes in many parts of the country?