Separate Chemistry II

Question 1

Explain why the test for any ion must be unique

Answer 1

You would never be able to know which specific ion it was if more than one ion gave the same result.

Question 2

Describe flame tests to identify the following ions in solids

Answer 2

Lithium ion, Li+ (red)
Sodium ion, Na+ (yellow)
Potassium ion, K+ (lilac)
Calcium ion, Ca2+ (orange-red)
Copper ion, Cu2+ (blue-green)
For each of the above you just need to hold a sample you wish to test on a wire in a roaring Bunsen burner flame and observe the flame colour.

Question 3

Describe tests to identify the following ions in solids or solutions as appropriate: (using sodium hydroxide solution)

Answer 3

Aluminium ion – White precipitate (dissolves when excess NaOH is added)
Calcium ion – White precipitate
Copper ion – Blue precipitate
Iron (II) ion – Green precipitate
Iron (III) ion – Brown precipitate
Ammonium ion – Pungent-smelling gas is produced. This gas produced turns damp red litmus paper blue.

Question 4

What is the chemical test for ammonia?

Answer 4

Makes damp red litmus paper turn blue. It also forms a white smoke of ammonium chloride when hydrogen chloride gas, from concentrated hydrochloric acid, is held near it.

Question 5

Describe the test to identify carbonate ions

Answer 5

Carbonate ion – using dilute acid and identifying the CO2 evolved.
Gas produced bubbled through limewater, if the limewater goes cloudy, the gas is CO2 (carbonates react with dilute acids to produce CO2.

Question 6

Describe the test to identify sulfate ions

Answer 6

Sulfate ion – using dilute hydrochloric acid and barium chloride solution.
Add dilute HCl followed by barium chloride solution. A white precipitate will form when sulfate ions are in this solution.

Question 7

Describe the tests to identify chloride, bromide and chloride ions

Answer 7

Chloride ion, Bromide ion, and Chloride ion – using dilute nitric acid and silver nitrate solution.
First add dilute nitric acid, followed by silver nitrate solution.
Chloride gives a white precipitate.
Bromide gives a cream precipitate.
Iodine gives a yellow precipitate.

Question 8

Describe that instrumental methods of analysis are available

Answer 8

Elements and compounds can be detected and identified using instrumental methods. These are accurate, sensitive and rapid instrumental methods include: gas chromatography and mass spectrometry.

Question 9

Explain why the alkanes are saturated hydrocarbons

Answer 9

They contain no C=C double bonds and are compounds made of hydrogen and carbon only.

Question 10

Recall the molecular formula of the alkenes

Answer 10

Ethene - C2H4
Propene - C3H6
Butene – C4H8
Pentene – C5H10

Question 11

Explain why the alkenes are unsaturated hydrocarbons

Answer 11

Contain one or more C=C double bonds and are compounds made of hydrogen and carbon only.

Question 11

Explain the addition reaction of ethene with bromine