1. Standard 5.a- Students know the observable properties of acids, bases, and salt solutions. 2/22/12

2. Identifying Acids An acid is a compound that produces hydronium ions (H 3 O + ) when dissolved in water. Ex. HCl + H 2 O  H 3 O + + Cl - Some general properties of acids include sour taste, sticky, smells bad, reactivity with metals, and ability to produce color changes in indicators. Acids donate H + ions

3. *Sour Taste and Reactivity with metals Foods that taste sour often contain acids Foods that contain acids, such as tomatoes, react with metals such as aluminum. Ex. Foils turn dark and may have holes. Food may acquire a metallic taste.

4. Color Changes in Indicators An indicator is any substance that changes color in the presence of an acid or base. Litmus paper is one of the most common indicators. Blue litmus turns red in the presence of an acid. Red litmus turns blue in the presence of a base.

5. Litmus Paper

7. Identifying Bases A base is a compound that produces hydroxide ions (OH - ) when dissolved in water. (Bases accept H + ions) Ex. NaOH  Na + + OH - Some general properties of bases include bitter taste, slippery feel, and ability to produce color changes in indicators. Unlike acids, most bases don’t react with metals.

8. *Bitter Taste Ex. Chocolate without sugar is bitter. Cacao bean contains a base. Cough syrups and many liquid medicines also contain similar bases.

9. Neutralization and Salts The reaction between an acid and a base is called neutralization. During neutralization, the positive ions (Na + ) in an acid combine with the negative ions (Cl - ) in a base to produce an ionic compound called a salt. At the same time, the hydronium ions from the acid combine with the hydroxide ions from the base to produce water.

10. Neutralization and Salts Ex. Fish contains bases and is bitter. Lemon contains acids and is sour. Acids in lemon juice react with bases in fish, so that fish doesn’t taste bitter.