© Oxford University Press 2008 Vitamin C in fruit keeps skin healthy, protects sperm and helps make bones. 5.1a Acids: harmful or useful? Vitamin C is ascorbic acid. Acids are vital to life. Can you think of any useful acids?

© Oxford University Press 2008 Ethanoic acid (vinegar) preserves pickles. Manufacturers add an acid to orange squash to stop it going off. 5.1a Acids: harmful or useful?

© Oxford University Press 2008 Picture of sardines Omega-3 fatty acids from oily fish defend your body against disease and repair damage. 5.1a Acids: harmful or useful?

© Oxford University Press 2008 …but outside the stomach it is always an irritant… Hydrochloric acid in your stomach helps digest food… …and can be corrosive. 5.1a Acids: harmful or useful?

© Oxford University Press 2008 Many acids can also be a nuisance. Can you think of any ‘annoying acids’? Methanoic acid makes bee, ant and nettle stings painful. 5.1a Acids: harmful or useful?

© Oxford University Press 2008 Car batteries contain sulfuric acid… …but it is corrosive and can burn living tissue if not disposed of properly. 5.1a Acids: harmful or useful?

© Oxford University Press 2008 Washing powders dissolve in water to make alkaline solutions. 5.1b Identifying acids and alkalis Alkalis are the chemical opposite of acids. They feel soapy.

© Oxford University Press 2008 Toothpaste helps protect teeth against acid erosion. 5.1b Identifying acids and alkalis You probably use one alkaline substance every day – toothpaste.

© Oxford University Press 2008 Companies use huge amounts of it to make paper, detergents and aluminium for fizzy drinks cans. 5.1b Identifying acids and alkalis Sodium hydroxide is an important alkali.

© Oxford University Press 2008 Which do you think are more dangerous – acids or alkalis? Jabir ibn Hayyan was a very important scientist. He worked in Iraq around the year 800. Jabir discovered how to make sulfuric acid, nitric acid and hydrochloric acid. He was the first person in the world to use the word ‘alkali’. Jabir wrote more than 100 books about his findings, which scientists found useful for hundreds of years. 5.1b Identifying acids and alkalis Discovering acids and alkalis

© Oxford University Press The pH scale is a measure of how acidic or alkaline a substance is. The scale goes from 1 to The diagram shows the colour that Universal Indicator changes for different pH values. Strong acidWeak acidNeutralWeak alkaliStrong alkali 5.1b The pH scale