Gcse: Tests for Anions and Cations

Question 1

Flame tests - lithium

Answer 1

Gives a red flame

Li+ ions

Question 2

Flame tests sodium

Answer 2

Gives a yellow flame

Na+ ions

Question 3

Flame tests potassium

Answer 3

Gives a lilac flame

K+ ions

Question 4

Flame tests calcium

Answer 4

Gives an orange red flame

Ca2+ ions

Question 5

Flame tests copper

Answer 5

Gives a blue green flame

Cu2+

Question 6

Flame tests method

Answer 6

Clean a nichrome wire loop by dipping it in hydrochloric acid and then rinsing it in distilled water

Dip the wire loop into a sample of the metal compound and put in the clear blue part of the Bunsen flame

Question 7

Precipitate test aluminium

Answer 7

Turn right at first but then re-dissolves in excess sodium hydroxide to form colourless solution

Al3+(aq) + 3OH-(aq) —-> Al(OH)3(s)

Then:
Al(OH)3(s) + OH- (aq) —-> Al(OH)4-(aq)

Question 8

Precipitate test calcium

Answer 8

Turns white

Ca2+(aq) + 2OH-(aq) —-> Ca(OH)2(s)

Question 9

Precipitate test copper

Answer 9

Turns blue

Cu2+(aq) + 2OH-(aq) —-> Cu(OH)2(s)

Question 10

Precipitate test iron II

Answer 10

Turns green

Fe2+(aq) + 2OH-(aq) —-> Fe(OH)2(s)

Question 11

Precipitate test iron III

Answer 11

Turns brown

Fe3+(aq) + 3OH-(aq) —-> Fe(OH)3(s)

Question 12

Test for ammonium ions

Answer 12

NH4+

Add sodium hydroxide to your solution of your substance and heat it,

test for ammonia gas by holding damp red litmus paper over it,

if the gas is ammonia the litmus paper will turn blue

Question 13

Halide test method

Answer 13

To test for halide ions and dilute nitric acid followed by a few drops of silver nitrate solution

Question 14

Halide test chloride ions

Answer 14

Forms white precipitate of silver chloride

Ag+(aq) + Cl-(aq) —-> AgCl(s)

Question 15

Halide test bromide ions

Answer 15

Forms cream precipitate of silver bromide

Ag+(aq) + Br-(aq) —-> AgBr(s)

Question 16

Halide test iodide ions

Answer 16

Forms yellow precipitate of silver iodide

Ag+(aq) + I-(aq) —-> AgI(s)

Question 17

Test for carbonates method

Answer 17

To test for carbonate ions in solution and some dilute acid

if there are carbonate ions present the mixture will fizz

this is because the carbonate will react with the acid to produce carbon dioxide gas

you can check to see if the gas is carbon dioxide by bubbling it through limewater

if it is the limewater turns milky

Question 18

Test for sulphate ions method

Answer 18

To test for sulphate ions in solution add dilute hydrochloric acid to the test sample (this stops any precipitation reactions not involving sulphate ions from taking place)

then add barium chloride solution

if sulphate ions are present a white precipitate of barium sulphate will form

Question 19

Flame photometry purpose

Answer 19

Flame photometry is an instrumental method that allows you to identify ions in a dilute solution

each ion produces a unique line spectrum

flame photometry works for mixtures this makes it better than flame tests