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
Organic
• 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
Mineral
• 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)
– Neutral solutions – purple – Acidic solutions – red
– Basic solutions – blue
Memory tip
R e
acid /base l u e
Litmus paper must always be damp when used....why is this?
Other indicators
• Use your books to complete the following chart.
Indicator 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.
Acids
• HCl
• HNO3
Alkalis
• 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.
