test for anions

Question 1

need to be able to describe the tests for these anions (3)

Answer 1

• carbonate ions
• halide ions
• sulfate ions

Question 1

test for carbonate ions

Answer 1

Add dilute acid
Bubble the gas released through limewater
Limewater turns cloudy if the carbonate ion is present
If a carbonate compound is present then fizzing / effervescence should be seen as CO2 gas is produced, which forms a white precipitate of calcium carbonate when bubbled through limewater:

Question 2

test for halide ions

Answer 2

Acidify the sample with nitric acid
Add silver nitrate solution AgNO3,
A silver halide precipitate forms is a halide ion is present - the precipitate is indicated by the state symbol (s)
The colour of the silver halide precipitate depends on the halide ion
Chloride ion forms white precipitate of silver chloride
Bromide ion forms a cream precipitate of silver bromide
Iodide ion forms a yellow precipitate of silver iodide

Question 3

test for sulfate ions

Answer 3

Acidify simple with dilute hydrochloric acid
Add a few drops of barium solution
A white precipitate of barium sulfate is formed, if the sulfate ion is present
Test can also be carried out with barium nitrate solution

Question 4

test for water ( chemical)

Answer 4

Anhydrous copper sulfate turns from white to blue on the addition of water

Question 5

physical test for water

Answer 5

A physical test to see if a sample of water is pure is to check its boiling point
A sample of the liquid is placed in a suitable container like a boiling tube and gently heated
Using a thermometer, you can check if the boiling point is exactly 100º
Any impurities will usually rise the boiling point and depress the melting point of a pure substance