SC25b Tests for Positive Ions

Question 1

test for ammonia?

Answer 1

damp red litmus paper turns blue

Question 2

testing for ammonium ions?

Answer 2

~glass rod is dipped in concentrated hydrochloric acid
~then held near the mouth of the test tube with the sample in
~if ammonium ions are present, a white smoke of ammonium chloride will form

Question 3

testing for positive ions?

Answer 3

~add a few drops of dilute sodium hydroxide solution to the test solution
~different metal ions will produce different coloured hydroxide precipitates

Question 4

problem with the initial test for positive ions?

Answer 4

some metals produce the same colour precipitates e.g. calcium and aluminium

Question 5

further test to distinguish precipitates?

Answer 5

~excess sodium hydroxide solution should be added to the test tube
~the precipitate of aluminium hydroxide will dissolve to form a colourless solution
~the precipitate of calcium hydroxide will not dissolve so will remain cloudy

Question 6

aluminium ion precipitate colour and effects of excess sodium hydroxide?

Answer 6

~white
~precipitate dissolves to form a colourless solution

Question 7

calcium ion precipitate colour and effects of excess sodium hydroxide?

Answer 7

~white
~precipitate does not dissolve

Question 8

copper ion precipitate colour? (test for positive ions)

Answer 8

~blue

Question 9

iron(II) ion precipitate colour? (test for positive ions)

Answer 9

~green

Question 10

iron(III) ion precipitate colour? (test for positive ions)

Answer 10

~brown

Question 11

word equation of copper ion with sodium hydroxide?

Answer 11

copper sulphate + sodium hydroxide –> copper hydroxide + sodium sulphate

Question 12

balanced equation of copper sulphate + sodium hydroxide

Answer 12

CuSO₄ (aq) + 2NaOH (aq) –> Cu(OH)₂ (s) + Na₂SO₄ (aq)