Revision for Acids and Indigestion

1. Revision for Acids and Indigestion Carbonates, Oxides and Hydroxides and their reaction with ACIDS

2. What is an indicator? An indicator is a chemical that turns a different colour depending on whether it is added to an acid or an alkali. Litmusis a commonly used indicator. It can be added to filter paper, or used as a liquid. Litmus is made from lichen, which grows on stone and rock. Litmus can be blue or red. Blue litmus turns red under acidic conditions (< pH 4.5), and red litmus turns blue under alkaline conditions (> pH 8.3). neutral alkali acid What colour do you think litmus is under neutral conditions?

3. strong acid weak acid neutral weak alkali strong alkali What is universal indicator? Universal indicator has a range of colours that show how weak or strong the acid or alkali is. What is the colour for a weak acid? What is the colour for a strong alkali? Universal indicator is made from a mixture of indicators. Why do you think it is more useful than litmus?

4. What is the pH scale? The strength of an acid or alkali is measured by the pH scale. Each universal indicator colour is given a pH value. Universal indicator can tell you the pH of a solution. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 strong acid neutral strong alkali What is the pH of a weak acid? What is the pH of a strong alkali?

5. What is neutralization? The chemical reaction between an acid and an alkali is called neutralization. What is the pH value of the mixture of salt and water? +  acid alkali salt + water The mixture of salt and water is neutral, so its pH is 7. The chemical reaction between an acid and an alkali can be written as: + acid alkali  salt + water

6. Neutralizing stings Bee stings are acidic. Wasp stings are alkaline. Which safe household substances could you use to treat a bee sting? Which safe household substances could you use to treat a wasp sting?

7. Making salts The salt produced by a neutralization reaction depends on the acid and the alkali used. Sodium chloride is produced by the reaction between hydrochloric acid and sodium hydroxide. hydrochloric acid sodium hydroxide sodium chloride + +  water Which acid and which alkali would be needed to make the salt potassium chloride? hydrochloric acid potassium hydroxide potassiumchloride + +  water

8. Naming salts • When an alkali reacts with hydrochloric acid, the salt produced is a chloride. • When an alkali reacts with sulfuric acid, the salt produced is a sulfate. • When an alkali reacts with nitric acid, the salt produced is a nitrate. • Which acid would be needed to make these salts? • copper nitrate • magnesium chloride • sodium sulfate

9. Making salts: word equations Complete these word equations: hydrochloric acid potassium hydroxide potassium chloride + +  water sodium hydroxide sodium sulfate + + sulfuric acid  water potassium hydroxide Potassium nitrate + + nitric acid  water

10. Indigestion remedies The acid in your stomach that helps you break down your food is called hydrochloric acid. It has a pH of between 1 and2. Indigestion and heartburn are caused by an excess of acid in your stomach. Indigestion remedies such as Milk of Magnesia contain antacids, like magnesium oxide and calcium carbonate. What do you think antacids do to the acid in your stomach?

11. Base or alkali? Bases are substances that react with acids, which include metals oxides, hydroxides and carbonates. bases: react with acids alkalis: soluble in water Alkalis are substances that react with acids and which are soluble in water. Copper oxide is a base, but not an alkali, because it reacts with acids, but does not dissolve in water. Sodium hydroxide is an alkali (and a base), because it reacts with acids and it is soluble in water.

12. Acid and carbonate When a carbonate reacts with an acid, it gives off carbon dioxide gas. How could you test the gas given off, to confirm that it is carbon dioxide? What would you observe in this test? carbon dioxide limewater

13. Acid and carbonate The products of the reaction between a carbonate and an acid are a salt, carbon dioxide and water. Calcium carbonate is a substance that is naturally found in the shells of sea creatures and snails. What salt do you think will be produced by the reaction of hydrochloric acid and calcium carbonate? hydrochloric acid calcium carbonate calcium chloride carbon dioxide + + +  water

14. The reactivity series Combining the information from all the reactions gives an overall order of reactivity called the reactivity series. One way to remember this order is to learn this silly sentence: please send charlie’s monkeys and zebras in large cages securely guarded!

15. Acid and metal Acids also react with metals to make a gas. When an acid reacts with a metal, the gas produced makes a lighted splint go pop. What is this gas? A salt is also produced during the reaction. What is the name of the salt that will be produced by the reaction of hydrochloric acid with calcium? hydrochloric acid calcium chloride + + calcium  hydrogen

16. How does acid rain work?

17. Effects of acid rain Acid rain has many damaging effects on the environment: • The acids in acid rain speed up the chemical weathering of rocks and buildings. • Rivers, lakes and streams become more acidic so that animals and plants cannot live in them. • Soil that becomes more acidic has fewer nutrients so trees and other plants cannot grow. Acid rain also damages trees by breaking down the waxy coating of leaves. What can be done to reduce acid rain and its effects?