Tests For Cations & Anions

Question 1

What do flame tests identify?

Answer 1

(Positive) metal ions

Question 2

Flame test: what colour is lithium?

Answer 2

Red

Question 3

Flame test: what colour is sodium?

Answer 3

Yellow

Question 4

Flame test: what colour is potassium?

Answer 4

Lilac

Question 5

Flame test: what colour is calcium?

Answer 5

Orange-red

Question 6

Flame test: what colour is copper?

Answer 6

Blue-green

Question 7

How to carry out a flame test (3)

Answer 7

Clean a nichrome wire loop by dipping in hydrochloric acid and rinsing in distilled water
Dip wire loop into sample of metal compound and put loop in blue part of Bunsen flame
Record flame colour

Question 8

What methods are there to test for cations?

Answer 8

Flame test
Coloured precipitate with NaOH
NaOH to ammonium ions

Question 9

How to carry out coloured precipitate cation test (2)

Answer 9

Add a few drops of sodium hydroxide solution to a solution of mystery compound
If a hydroxide precipitate forms, use its colour to tell which metal was in the compound

Question 10

Coloured precipitate test: what colour is aluminium?

Answer 10

White at first but then redissolves in excess NaOH to form a colourless solution

Question 11

Coloured precipitate test: what colour is calcium?

Answer 11

White

Question 12

Coloured precipitate test: what colour is copper?

Answer 12

Blue

Question 13

Coloured precipitate test: what colour is iron II?

Answer 13

Green

Question 14

Coloured precipitate test: what colour is iron III?

Answer 14

Brown

Question 15

What test for cations do you do after the flame test and the coloured precipitate test?

Answer 15

Add NaOH to ammonium ions to test for ammonia

Question 16

How do you test for ammonia ions? (3)

Answer 16

Add NaOH to substance and gently heat it
If ammonia gas is given off there are ammonium ions in the substance
Test for ammonia gas - turns damp red litmus paper blue

Question 17

How to test for halide ions (method + outcomes)

Answer 17

Add dilute nitric acid followed by a few drops of silver nitrate solutution
A chloride gives a white precipitate (silver chloride)
A bromide gives a cream precipitate (silver bromide) An iodide gives a yellow precipitate (silver iodide)

Question 18

Silver nitrate solution, halide test: what colour precipitate is chloride?

Answer 18

White

Question 19

Silver nitrate solution, halide test: what colour precipitate is bromide?

Answer 19

Cream

Question 20

Silver nitrate solution, halide test: what colour precipitate is iodide?

Answer 20

Yellow

Question 21

How to test for carbonates (3)

Answer 21

Add dilute acid
If carbonate ions are present the mixture will fizz because carbon dioxide is produced
Test for carbon dioxide by bubbling it through limewater which turns milky

Question 22

How to test for sulphate ions (3)

Answer 22

Add dilute hydrochloric acid
Then add barium chloride solution
If sulphate ions are present in the solution, a white precipitate (barium sulphate) forms

Question 23

Sulphate ions, barium chloride test: why do you add hydrochloric acid?

Answer 23

To stop any precipitation reactions not involving sulphate ions from taking place