1. Neutralisation
Noadswood Science, 2012

2. Neutralisation To understand neutralisation reactions
Friday, April 21, 2017
Neutralisation
To understand neutralisation reactions

3. Acid Or Alkali Are the following acids or alkalis? Hydrochloric (HCl)
Sodium hydroxide (NaOH)
Sulphuric (H2SO4)
Nitric (HNO3)
Ammonium hydroxide (NH4OH)
Toothpaste
Lemon juice
Oven cleaner
Stomach fluid
Indigestion tablets
Acid (Hydrochloric acid)
Alkali
Acid (Sulphuric acid)
Acid (Nitric acid)
Alkali
Alkali
Acid
Alkali
Acid (Stomach acid)
Alkali

4. Acids & Alkalis Strong acid Weak acid Neutral Weak alkali
Strong alkali
Stomach acid
Vinegar
Skin
Pure water
Indigestion tablets
Washing powder
Oven cleaner
Lemon juice
Fizzy drinks
Milk
Blood
Toothpaste

5. Acid + Alkali What happens when we mix and acid and alkali?
Mixing an acid and alkali results in a chemical reaction, forming new products…

6. Neutralisation
The chemical reaction between an acid and alkali is called neutralisation
Acid
Alkali
Salt + Water
If you add just the right amount of acid and alkali together a neutral solution is formed (the pH value gets close to pH 7 - neutral)

7. Experiment
Your task is to see if you can undertake a neutralisation reaction
In a boiling tube add a small amount of acid
Using a pipette add one drop of alkali at a time, until you produce a neutral solution

8. Chemical Reaction Acid Alkali Salt Water
The chemical reaction between an acid and alkali is: -
Acid
Alkali
Salt
Water

9. Acids Substances with a pH of less than 7 are acids
The stronger the acid, the lower the pH number
Acids turn blue litmus paper red and turn universal indicator red if they are strong, and orange or yellow if they are weak
Acid
Formula
Strength
Sulphuric
H2SO4
Strong
Hydrochloric
HCl
Nitric
HNO3
Ethanoic (vinegar)
CH3COOH
Weak

10. HCl(aq) → H+(aq) + Cl-(aq)
Acids
When acids dissolve in water they produce hydrogen ions, H+
For example, looking at hydrochloric acid: -
HCl(aq) → H+(aq) + Cl-(aq)

11. Acids & Bases
When acids react with bases, a salt and water are made – neutralisation
Acid + Metal Oxide → Salt + Water
Acid + Metal Hydroxide → Salt + Water

12. Acid + Metal Carbonate → Salt + Water + Carbon Dioxide
Acids & Carbonates
When acids react with carbonates a salt, water and carbon dioxide are made
Acid + Metal Carbonate → Salt + Water + Carbon Dioxide
* Carbon dioxide causes bubbling during the reaction, and can be detected using limewater

13. Acid + Metal → Salt + Hydrogen
Acids & Metals
Acids will react with reactive metals to make a salt and hydrogen
Acid + Metal → Salt + Hydrogen
*Hydrogen causes bubbling during the reaction, and can be detected using a lighted splint

14. Bases
Substances that can react with acids and neutralise them to make a salt and water are called bases
Bases are usually metal oxides or metal hydroxides, e.g. copper oxide and sodium hydroxide are bases
Type Of Compound
Formula
Strength
Metal Hydroxides
OH-
Water + Salt
Metal Oxides
O2-
Metal Carbonates
CO32-
Water + Salt + CO2

15. Alkalis Bases that dissolve in water are called alkalis
Alkaline solutions have a pH of more than 7 (the stronger the alkali, the higher the pH number) – alkalis turn red litmus paper blue and they turn universal indicator dark blue or purple if they are strong, and blue-green if they are weak
Alkalis
Formula
Strength
Sodium Hydroxide
NaOH
Strong
Potassium Hydroxide
KOH
Calcium Hydroxide
Ca(OH)2
Ammonium Hydroxide
NH4OH
Weak

16. NaOH(aq) → Na+(aq) + OH-(aq)
Alkalis
When alkalis dissolve in water they produce hydroxide ions, OH-
For example, looking at sodium hydroxide: -
NaOH(aq) → Na+(aq) + OH-(aq)

17. H+(aq) + OH-(aq) → H2O(l)
Neutral
Neutral solutions have a pH of 7
They do not change the colour of litmus paper, but they turn universal indicator green (e.g. water is neutral)
When the H+ ions from an acid react with the OH- ions from an alkali, a neutralisation reaction occurs to form water: -
H+(aq) + OH-(aq) → H2O(l)
In the reaction between sodium hydroxide and hydrochloric acid Na+ ions and Cl- ions left over – these form sodium chloride, NaCl

18. Stings A bee sting is acidic A wasp sting is alkaline
Why can bicarbonate of soda (pH 9) be used to treat a bee sting?
Why can vinegar (pH 3) be used to treat a wasp sting?
Adding just the right amount of acid or alkali to the sting causes it to neutralise!

19. Anagrams