Chapter 3.2L Acids, Bases, and Salts

Acids An acid is any compound that increase the number of hydrogen ions when dissolved in water, and who taste sour and cause a color change of certain compounds.

Properties of Acids Many acids taste sour – like all citrus fruits (oranges, lemons, and limes) – you should not taste something just to find out if it is an acid though. Many acids are corrosive – they destroy body tissue and clothing. Many are also poisonous. Acids can react with some metals to make hydrogen gas. Sometimes is can react to make carbon dioxide. Solutions of acids can conduct an electric current.

Detecting Acids An indicator can be used to test for an acid. An indicator is a substance that changes color in the presence of an acid or base. Usually litmus paper is used – usually this is blue (to test acids) and turns red.

Uses of Acids Sulfuric acid is used in the production of metals, paper, paint, detergents, and fertilizers. It is also used in car batteries. Nitric acid is used to make fertilizers, rubber, and plastics. Hydrochloric acid is used to make metals, and to keep swimming pools algae free. It is also found in your stomach, for digestion. Citric acid is found in orange juice. Carbonic acid is used in sodas to give it fizz.

Strong Versus Weak An acid is classified as weak or strong by the amount of hydrogen ions produced when added to water. If all the molecules of an acid break apart in water to produce hydrogen ions, it is a strong acid. Strong acids are sulfuric acid, nitric acid, and hydrochloric acid. When few molecules break apart to form hydrogen ions it is a weak acid. Acetic acid (vinegar), citric acid, carbonic acid, and phosphoric acid are all weak.

Bases A base is any compound that increases the number of hydroxide (OH) ions when dissolved in water, who taste bitter, feel slippery, and change the color of certain compounds.

Properties of Bases Soap would be an example of a base, if you’ve tasted soap you know it is bitter and it is slippery. Bases can be corrosive. Solutions with bases can conduct an electric current.

Detecting Bases Bases change the color of an indicator. For bases we use red litmus paper and it will turn blue.

Uses of Bases Sodium hydroxide can be used to make soap and paper, also used in oven cleans, products that unclog drains. Bases can harm your skin so be very careful when using a base. Calcium hydroxide is used to make mortar, cement, and plaster Ammonia is found in household cleaners and in fertilizers. Magnesium hydroxide and aluminum hydroxide are used in antacids.

Strong Versus Weak When all the molecules of a base break apart in water to form hydroxide ions, it is a strong base. Strong bases are sodium hydroxide, calcium hydroxide, and potassium hydroxide. A weak base is when a few molecules produce hydroxide ions. Weak bases are ammonia, magnesium hydroxide, and aluminum hydroxide.

Acids and Bases Neutralize One Another Acids and bases neutralize one another because they hydrogen ions (H) from the acid and the hydroxide ions (OH) from the base will form water.

The pH Scale The pH scale helps us describe how acidic or basic something is. The pH of a solution measures the H ion concentration. pH of 7 is neutral. Bases have a pH of greater than 7. Acids have a pH of less than 7.

Using Indicators to Determine pH There are paper strips or solutions that will change to different colors based on the pH of the solution being tested.

pH and the Environment Different living things have different pH requirements. Pine trees like acidic soil – pH between 4 and 6. Lettuce likes basic soil, pH between 8 and 9. Fish like a pH of about 7.

Salts Salt is an ionic compound formed from the positive ion of a base and the negative ion of an acid.

Uses of Salts Sodium chloride is used to season food, to produce lye, hydrochloric acid, and baking soda. Calcium sulfate is made into plasterboard (used in construction). Sodium nitrate is used as a food preservative. Calcium carbonate makes limestone, chalk, and sea shells.