Acids and Bases and Salts – revisited 

What is an Acid? A substance which reacts with a base to form salt and water. Sour taste pH less than 7 There are two types of acids; Organic acids – which contain carbon Mineral acids – which contain inorganic compounds.

Organic and Mineral Acids Ethanoic acid CH3COOH In vinegar Methanoic acid HCOOH In ant and nettle stings Citric acid C6H8O7 In lemons, oranges etc. Present in animal and plant material. weak Carbonic acid H2CO3 In fizzy drinks Weak Hydrochloric acid HCl Oven cleaner Dilute form in stomach Nitric acid HNO3 Ferlilisers and explosives Sulfuric acid H2SO4 Car batteries, paints and detergents Strong and corrosive

Indicators Litmus (plant extract from lichens) Memory tip Neutral solutions – purple Acidic solutions – red Basic solutions – blue Memory tip R e acid /base l u Litmus paper must always be damp when used....why is this?

Other indicators Use your books to complete the following chart. Colour in Acid Neutral Colour Colour in alkali

Universal Indicator Mixture of indicator dyes. Gives a range of colours.

pH Scale Danish chemist Søren Sørensen worked in the Carlsberg breweries and was interested in checking the acidity of beer. He developed the pH scale. pH can be measured with universal indicator and also with a pH meter.

pH scale and examples Use your books to help you fill in the following chart. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 water

Activity Answer questions 1 – 7 on page 140

Acid and Alkali Solutions The importance of ions Both acid and alkai solutions conduct electricity well. This means there is a prsence of ions. Acids dissolve in water to produce hydrogen ions HCl H+ (aq) + Cl- (aq) The term pH is taken from „potenz Hydrogen“ – the power of the hydrogen ion concentration.

Alkali Solutions Alkali dissolve in water to produce hydroxide ions . NaOH Na+ (aq) + OH- (aq)

Activity - Determine the ions for the following acids and alkali. Alkalis HCl HNO3 NaOH KOH

Activity Answer the questions on page 141

Metal and Non-Metal Oxides Read the section on metal and non-metal oxides on pages 141 and 143. What does amphoteric mean? Answer question on page 143.