1. C2- Chemistry Analysing substances, making salts, acids and bases
Additional Science
C2- Chemistry Analysing substances, making salts, acids and bases

2. Analysing substances
Instrumental methods of analysing substances such as elements and compounds are;
accurate, rapid and sensitive
Paper chromatography can be used to detect additives in food.
Artificial colours can be identified.

3. Analysing substances Lid to prevent evaporation of the solvent.
Unknown sample.
Known samples.
Pencil line; starting point, pencil does not dissolve in the solvent.
Solvent; dissolves the colours and is absorbed through the paper.
The colour dots from the unknown sample which match the known samples can be identified as to whether the additive is safe or not.

4. Analysing substances
Gas chromatography linked to mass spectroscopy (GC-MS) is an example of an instrumental method:
Gas chromatography separates mixtures of compounds, it uses a column packed with solid.
The substance to be analysed is carried
through the column using a gas
The time taken for a substance to travel through the column can be used to help identify the substance

5. The number of peaks corresponds to the number of compounds present
The position of the peak is the ‘retention time’, in other words how long they have spent in the column

6. Analysing substances
The gas chromatography column can be linked to a mass spectrometer which can identify substances quickly and accurately and in very small quantities.
The mass spectrometer can give the relative molecular mass of the substances (you look at the molecular ion peak on a graph)

7. Making salts H+(aq) + OH-(aq)  H2O (l)
State symbols are shown after substances in reactions
(s)= solid
(l)= liquid
(aq) = aqueous (dissolved in water)
(g) = gas

8. Making salts Soluble salts can be made by reacting acids with:
1. metals – not all metals are suitable; some are too reactive and others are not reactive enough (MASH)
2. insoluble bases – the base is added to the acid until no more will react and the excess solid is filtered off (copper sulphate)
3. alkalis – an indicator can be used to show when the acid and alkali have completely reacted to produce a salt solution. (neutralisation)

9. Making salts Metal + Acid  Salt + Hydrogen
Soluble salts can be made by reacting acids with:
1. metals – not all metals are suitable; some are too reactive and others are not reactive enough (MASH)
Metal + Acid 
Salt + Hydrogen

10. Making salts Hydrochloric acid produces metal chlorides
e.g. Sodium chloride
Sulphuric acid produces metal sulphates
e.g. Sodium Sulphate
Nitric acid produces metal nitrates
e.g. sodium nitrate

11. Making salts Soluble salts can be made by reacting acids with:
2. insoluble bases – the base is added to the acid until no more will react and the excess solid is filtered off (copper sulphate)

12. Making salts Acid + Alkali  Salt + Water H+(aq) + OH-(aq)  H2O (l)
Soluble salts can be made by reacting acids with:
3. alkalis – an indicator can be used to show when the acid and alkali have completely reacted to produce a salt solution. (neutralisation)
Acid + Alkali 
Salt + Water
Hydrochloric Sodium
acid hydroxide
Sodium
Chloride
Water
H+(aq) + OH-(aq)  H2O (l)

13. Salts solutions (aq) can be crystallised to produce solid salts (s)
Making salts
Salts solutions (aq) can be crystallised to produce solid salts (s)

14. Making salts
Insoluble salts can be made by reacting two soluble salts together. This is called a precipitation reaction.
Soluble except when with silver, mercury or lead.
All soluble
Soluble except when with silver, lead, mercury, barium, strontium and calcium.

15. Making salts
Insoluble salts can be made by reacting two soluble salts together. This is called a precipitation reaction.
All insoluble except for NH4+, barium and those of group 1 elements
All insoluble except for calcium, barium and group 1
All insoluble except when with NH4+ and group 1 elements

16. An example precipitation reaction
Making salts
An example precipitation reaction
Silver Sodium
nitrate chloride
Sodium
nitrate
Silver
chloride
AgNO3(aq) + NaCl(aq) → NaNO3(aq) +AgCl(s)

17. Making salts
Precipitation reactions are used to remove unwanted ions from solutions, for example to treat drinking water or treating effluent

18. Acids and bases
Metal oxides and metal hydroxides are bases e.g. sodium hydroxide, copper oxide.
If the hydroxides are soluble they are called alkalis
Hydrochloric Sodium
acid hydroxide
Sodium
Chloride
Water
The name of the salt produced when an acid and alkali react depends on the acid used and the metal in the base

19. Acids and bases
Ammonia (NH3) dissolves in water to form an alkali solution, NH3 (aq).
It is used to produce ammonium salts
These salts are used as fertilisers

20. Acids and bases
The presence of H+ ions makes solutions acidic.
The presence of OH- ions make solutions alkali. 1 2 14 13 12 11 10 9 8 7 6 5 4 3
Strong acid
Neutral
Strong alkali
Weak acid
Weak alkali
More alkali
More acid
More OH- ions
More H+ ions

21. Acids and bases Acid + Alkali  Salt + Water
In neutralisation reactions, hydrogen ions react with hydroxide ions to produce water.
Acid + Alkali 
Salt + Water
nitric potassium
acid hydroxide
potassium
nitrate
Water
H+(aq) + OH-(aq)  H2O (l)