RP4- Tests for Ions

Question 1

Describe the test for a sulfate ion (incl. expected result)

Answer 1

add acidified BaCl2
a white ppt. will form

Question 2

Describe the test for ammonium ions (incl. expected result)?

Answer 2

warm with NaOH
test gas with damp red litmus
litmus will turn blue

Question 3

Describe the test for halide ions (incl. expected result)?

Answer 3

add acidified silver nitrate
ppt will form

Question 4

Describe the colour of the ppt for Cl-, Br-, and I- ions

Answer 4

Cl-: white ppt
Br-: off-white ppt
I-: yellow ppt

Question 5

Explain why silver nitrate solution must be acidified when used to test for halide ions

Answer 5

Prevents the formation of silver carbonate (Ag 2 CO 3 )
This forms as a result of atmospheric CO 2 dissolving in the solution

Question 6

Give a test for carbonate ions

Answer 6

Add HCl, H2SO4 or HNO3 . Test gas evolved with limewater (forms white ppt due to CO2)

Question 7

Explain why acidified barium chloride or acidified silver nitrate solution react with carbonate ions

Answer 7

Both solutions contain acid that reacts with the carbonate ions to produce CO2 gas
2H+ (aq) + CO32- (aq) –> H2O(l) + CO2(g)

Question 8

Give the first step to test any unknown inorganic solid

Answer 8

dissolve in distilled water

Question 9

Test for hydroxide ions

Answer 9

Add a solution of Mg 2+ ions (e.g. MgCl 2 (aq)) forms white ppt of Mg(OH) 2
Mg2+(aq) + 2OH-(aq) –> Mg(OH)2(s)

Question 10

Explain how ammonia solution can be used to distinguish between silver halide ppts.

Answer 10

Add ammonia
Cl- dissolves
Br- dissolves in excess
I - insoluble in NH3

Question 11

How would two tests on the same solution show it contains HCl?
test 1- effervescence in presence of NA2CO3
test 2- white ppt, when AgNO3 is added

Answer 11

effervescence shows H+ ions are present
white ppt so Cl- ions are present