Section 1: Acids and Bases

• Acids

  • Although some acids can burn and are dangerous to handle, most acids in foods are safe to eat.

    • What acids have in common, however, is that they contain at least one hydrogen atom that can be removed when the acid is dissolved in water.

  • Acid: a substance that produces hydrogen ions in a water solution. It is the ability to produce these ions that gives acids their characteristic properties.

  • Hydronium Ions: H3O+ ions

  • All acids taste sour.

    • Taste never should be used to test for the presence of acids. Some acids can damage tissue by producing painful burns.

  • Acids are corrosive. Some acids react strongly with certain metals, seeming to eat away the metals as metallic compounds and hydrogen gas form.

  • Indicator: an organic compound that changes color in acid and base.

  • Your stomach uses hydrochloric acid to help digest your food.

  • Many acids can burn, but sulfuric acid can burn by removing water from your skin as easily as it takes water from sugar.

• Bases

  • Although you can eat some foods that contain acids, you don’t consume many bases.

  • One characteristic of bases is that they feel slippery, like soapy water.

  • Base: Any substance that forms hydroxide ions, OH- , in a water solution; any substance that accepts H+ from acids.

  • In the pure, undissolved state, many bases are crystalline solids.

  • Like strong acids, strong bases are corrosive, and contact with skin can result in severe burns.

    • Taste and touch never should be used to test for the presence of a base.

  • Like acids, bases react with indicators to produce changes in color.

• Solutions of Acids and Bases

  • Compounds that can form hydroxide ions (OH–) in water are classified as bases.

  • When bases that contain –OH dissolve in water, the negative areas of nearby water molecules attract the positive ion in the base.

    • The base dissociates into a positive ion and a negative ion—a hydroxide ion (OH–).

  • Ammonia is a base that does not contain -OH.

  • A reaction between sodium hypochlorite and ammonia produces the toxic gases hydrazine and chloramine.

  • Solutions of both acids and bases produce some ions that are capable of carrying electric current to some extent.

Section 2: Strength of Acids and Bases

• Strong and Weak Acids and Bases

  • Some acids must be handled with great care.

  • The strength of an acid or base depends on how many acid or base particles dissociate into ions in water.

  • Strong Acid: when it is dissolved in water, nearly all the acid molecules dissociate into ions.

  • Weak Acid: When it is dissolved in water, only a small fraction of the molecules dissolve in water.

  • Ions in solution can conduct an electric current.

    • The more ions a solution contains, the more current it can conduct.

  • Strong Base: dissociates completely in solution.

  • Weak Base: one that does not dissociate completely.

  • The terms dilute and concentrated are used to indicate the concentration of a solution, which is the amount of acid or base dissolved in the solution.

• pH of a Solution

  • pH: a measure of the concentration of H+ ions in a solution.

  • The pH measures how acidic or basic a solution is.

  • Solutions with a pH lower than 7 are described as acidic, and the lower the value is, the more acidic the solution is.

  • Solutions with a pH greater than 7 are basic, and the higher the pH is, the more basic the solution is.

  • A solution with a pH of exactly 7 indicates that the concentrations of H+ ions and OH- ions are equal.

  • One way to determine pH is by using a universal indicator paper.

  • An instrument called a pH meter is another tool to determine the pH of a solution.

  • In order to carry out its many functions properly, the pH of blood must remain between 7.0 and 7.8.

    • You can eat foods that are acidic without changing the pH of your blood.

  • Buffers: solutions containing ions that react with additional acids or bases to minimize their effects on pH.

Section 3: Salts

• Neutralization: a chemical reaction between an acid and a base that takes place in a water solution.

  • Antacids contain bases or other compounds containing sodium, potassium, calcium, magnesium, or aluminum that react with acids to lower acid concentration.

  • Salt: a compound formed when the negative ions from an acid combine with the positive ions from a base.

• Salts

  • Most salts are composed of a positive metal ion and an ion with a negative charge.

  • Salt is essential for many animals large and small.

  • Humans need salt too, especially because we lose salt in perspiration.

• Titration: in which a solution of known concentration is used to determine the concentration of another solution.

  • Sometimes you need to know the concentration of an acidic or basic solution.

  • Titration involves a solution of known concentration, called the standard solution.

  • If the unknown is an acid, a standard base solution is used.

  • Many natural substances are acid–base

    indicators.

• Soaps and Detergents

  • Soaps: organic salts.

    • They have a non-polar organic chain of carbon atoms on one end and either a sodium or potassium salt of a carboxylic acid.

    • To make an effective soap, the acid must contain 12 to 18 carbon atoms.

    • One problem with all soaps, however, is that the sodium and potassium ions can be replaced by ions of calcium, magnesium, and iron found in some water known as hard water.

  • Detergents are synthetic products that are made from petroleum molecules, instead of from natural fatty acids like their soap counterparts.

  • Most detergents contain additional ingredients called builders and surfactants to enhance sudsing and further improve cleaning in hard water.

• Versatile Esters

  • In a way esters can be thought of as the organic counterparts of salts.

  • The difference is that salts are made from bases and esters come from alcohols that are not bases but have a hydroxyl group.

  • The reaction to prepare esters involves removing a molecule of water from an acid and an alcohol.

  • Synthetic fibers known as polyesters are polymers; that is, they are chains containing many or poly esters.