Tests For Cations + Anions

Question 1

Cations flame test explained

Answer 1

Pour a few drops of concentrated hydrochloric acid onto a watch glass, dip the nichrome loop wire in this. Then place in a blue flame until no colour is visible (sterilisation). Then place some solid onto a separate watch glass and dip the same nichrome wire into this. Place in a blue flame and record the colour of the flame produced.

Question 2

What colour does Li+ give out in a flame test?

Answer 2

Crimson

Question 3

What colour does Na+ give out in a flame test?

Answer 3

Yellow

Question 4

What colour does K+ give out in a flame test?

Answer 4

Lilac

Question 5

What colour does Ca 2+ give out in a flame test?

Answer 5

Red/orange

Question 6

What colour does Cu 2+ give out in a flame test?

Answer 6

Green

Question 7

Cations with sodium hydroxide experiment

Answer 7

Half fill 100 cm^3 beaker with dilute sodium hydroxide solution. Pour a small volume of each named solution into a test tube and pour an equal volume of alkali (sodium hydroxide) in the same test tube. Stir with glass rod. Record observations

Question 8

What does Cu2+ produce during the cations with sodium hydroxide test?

Answer 8

Blue precipitate

Question 9

What does Fe2+ produce during the cations with sodium hydroxide test?

Answer 9

Green precipitate

Question 10

What does Fe3+ produce during the cations with sodium hydroxide test?

Answer 10

Brown precipitate

Question 11

What does Al3+ produce during the cations with sodium hydroxide test?

Answer 11

White precipitate which dissolves when excess sodium hydroxide is added

Question 12

What does Mg2+ produce during the cations with sodium hydroxide test?

Answer 12

White precipitate

Question 13

What does Ca2+ produce during the cations with sodium hydroxide test?

Answer 13

White precipitate with red flame

Question 14

Anions - halide test

Answer 14

Pour 1cm^3 sample into test tube and acidify with equal volume of nitric acid and silver nitrate (AgNO3)

Question 15

Halide test AgCl

Answer 15

NaCl (aq) + AgNO3 (aq) —> NaNO3 (aq) + AgCl (s)
Ionic : Ag+ + Cl- —> AgCl
White precipitate

Question 16

Halide test NaBr

Answer 16

NaBr (aq) + AgNO3 (aq) —> NaNO3 (aq) + AgBr (s)
Ionic : Ag+ + Br- —> AgBr
Cream precipitate

Question 17

Halide test AgI

Answer 17

NaI (aq) + AgNO 3 (aq) —> NaNO3 (aq) + AgI (s)
Ionic : Ag+ + I- —> AgI
Yellow precipitate

Question 18

Sulphate test anions

Answer 18

On solution: pour 1cm3 of sample into the test tube and acidify with equal volume of dilute hydrochloric acid (remove any unwanted impurities) + add 1cm^3 barium chloride (DONT use sulphuric acid)
If sulphur present white precipitate forms

Question 19

Sulphate test equations using Potassium sulphate

Answer 19

K2SO4 (aq) + BaCl2 (aq) —> 2KCl (aq) + BaSO4 (s)

Ionic : SO4 2- + Ba 2+ —> BaSo4 (s)

Question 20

Carbonate test

Answer 20

Pour 1cm^3 into test tube with dilute hydrochloric acid, if bubbles occur, extract using a pipette and bubble through limewater. If the limewater goes from clear/colourless to cloudy this means CO2 is present meaning the carbonate ion is present in the sample we tested on.

Question 21

Carbonate test with MgCO3 equations

Answer 21

MgCO3 (s) + 2HCl —> MgCl2 (aq) + H2O(l) + CO2 (g)

Ionic : Co3 2- + 2H+ —> CO2 (g) + H2O (l)