Acids and Bases

Acids An acid is a substance that tastes sour, reacts with metals, and turns blue litmus paper red. Acids react with certain metals to produce hydrogen gas. Not all metals react this way, but magnesium, zinc, and iron do. When they react, the metals seem to disappear in the solution. This observation is one reason acids are described as corrosive, meaning they "eat away" at other materials.

Indicators An indicator is a compound that changes color when in contact with an acid or base. Litmus is an example of an indicator. Acids (like vinegar and lemon juice) turn blue litmus paper red. Sometimes chemists use other indicators to test for acids, but litmus is one of the easiest to use.

Bases A base is a substance that tastes bitter, feels slippery, and turns red litmus paper blue. Bases are often described as the "opposites" of acids. Common bases include sodium hydroxide, calcium chloride, and ammonia. Bases turn red litmus paper blue.

Uses of Acids and Bases Acids play an important role in our nutrition and are found in valuable products used in homes and industries. Acids in our foods are weak – so they are safe to eat! The reactions of bases make them valuable raw materials for a range of products. Acid examples: Oranges – ascorbic acid (vitamin c) Leafy vegetables – folic acid Fertilizers & batteries Base examples: Cooking – baking soda Cement, mortar, and soaps

Strengths of Acids and Bases Acids and bases may be strong or weak. Strength refers to how well an acid or base produces ions in water. To describe the concentration of ions, chemists use a numerical scale called pH. The pH scale is a range of values from 0 to 14.

pH Scale A number scale used to describe the strength of an acid or base. The stronger the acid, the lower the pH. The stronger the base, the higher the pH. pH scale ranges from 1 – 14 pH scale 1 – 6 indicates an acid pH scale 8 – 14 indicates a base pH of 7 is neutral

pH Scales

How to Neutralize an Acid You can neutralize an acid by combining it with a base. The stronger the acid, the stronger the base that is needed to neutralize it. Ex: an acid with a pH of 2 will need to be combined with a base that has a pH of 12.

Acid Rain Any precipitation that has a pH that is lower than 5.8 is considered to be acid rain. Acid rain is caused by pollution and natural sources (ex: volcanic eruption) that put sulfur and nitrogen oxides in the atmosphere. Acid rain can cause problems in the habitats, toxic metals in plants and animals, erosion of stone on buildings and statues, etc…