8.3 Qualitative analysis

Question 1

What does qualitative analysis rely on

Answer 1

Simple observations rather than measurements and can be carried out quickly on a test tube scale
Observations may be gas bubbles, precipitates, colour changes or identification of gases

Question 2

What is the test for carbonates

Answer 2

1. Add dilute nitric acid to the solid or solution to be tested
2. If you see bubbles, the unknown compound could be a carbonate.
3. To prove that the gas is carbon dioxide, bubble the gas through calcium hydroxide solution, a white precipitate forms which turns the lime water cloudy

Question 3

What is the test for sulfates

Answer 3

Aqueous barium ions are added to a solution of an unknown compound
Usually in barium chloride or nitrate, use nitrate if you want to do a halide test after

Question 4

What is the test for halides

Answer 4

Most are soluble in water but silver halides are insoluble
Aqueous silver ions react with aqueous halide ions to form precipitates of silver halides as shown by the general equation
Ag+(aq) + X-(aq) -> AgX(s)
Add silver nitrate, silver halide precipitates different colours, add aqueous ammonia to test the solubility of the precipitate

Question 5

What colours does a solution turn if a halide is present

Answer 5

Chloride - white
Bromide - Cream
Iodide - yellow

Question 6

What is the correct order to test for anions

Answer 6

Carbonate
Sulfate
Halides

Question 7

What are barium meals used for

Answer 7

Enable doctors to see the outline of the gllet, stomach and upper small intestine in order to identify abnormalities such as ulcers or tumors

Question 8

What is the test for ammonium ions

Answer 8

Aqueous sodium hydroxide is added to a solution
Ammonia gas is produced, unlikely to see bubbles as ammonia is very soluble in water
May be able to smell, test with moist pH indicator paper. Ammonia is alkaline so paper will turn blue