Chapter 10 ComMon Acids and Alkalis
10.1 Acids and Alkalis
1. Acids taste sour. Many fruits contain acids.
2.The three mineral acids commonly found in the laboratory are hydrochloric acid, sulphuric acid and nitric acid.
3. Alkalis taste bitter and feel soapy or slippery.
4.The common alkalis found in the laboratory are sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution and ammonia solution.
10.2 Acid-Alkali Indicators
1. An acid-alkali indicator shows different colours in acids and alkalis. It can be used to test acids and alkalis. 2. Natural indicators can be made from some deeply coloured plants. 3. Acids turn blue litmus paper red whereas alkalis turn red litmus paper blue. Distilled water does not change the colour of litmus paper. It is a neutral substance. 4. The pH value shows the degree of acidity or alkalinity of a substance. 5.The pH value of a substance can be measured by using universal indicator, pH paper or a pH meter.
6. Low pH values mean high acidity (or low alkalinity).
7.High pH values mean high alkalinity (or low acidity).
8. Substances with pH values < 7 :acidic;
pH values = 7 :neutral;
pH values > 7:alkaline.
10.3 Acids and Corrosion
1. Dilute acids react with some metals and produce hydrogen. 2.Test for hydrogen: Put a burning splint near the mouth of a test tube containing the gas. If the gas is hydrogen, it burns with a 'pop' sound.
3.The rate of reaction of some metals with dilute hydrochloric acid or dilute sulphuric acid:
maznesium > zinc> iron > copper (no reaction)
4. Carbonates react with acids and give carbon dioxide.
5. Marble and limestone mainly contain calcium carbonate. They are used as building materials and they can...