Identification

Question 0

Test for carbon dioxide:

Answer 0

Bubble the gas through limewater (calcium hydroxide - CaOH). Carbon dioxide turns limewater a milky color.

Question 1

Test for ammonia:

Answer 1

• use a drop of concentrated HCl; dense white fumes should be produced
• use damp red litmus paper; it should turn blue

Question 2

Test for hydrogen:

Answer 2

Use a lighted splinter. The gas should burn with a ‘pop’ sound.

Question 3

Test for oxygen:

Answer 3

Use a glowing splinter. The gas should rekindle the glowing splinter.

Question 4

Test for sulphur dioxide (SO2):

Answer 4

Bubble the gas through acidified potassium dichromate (K2Cr2O7). The orange solution should turn green.

Question 5

Test for carbonate:

Answer 5

Add dil. HCl and pass the liberated gas through limewater. It should turn milky and form effervescence (lots of bubbles).

Question 6

Test for chloride/bromide/iodide:

Answer 6

Add dil. HNO3 + aq. silver nitrate (AgNO3) OR dil. lead nitrate (Pb(NO3)2)

Chloride should form white ppt. insoluble in acid, bromide should form cream ppt., and iodide should form yellow ppt., with same characteristic.

Question 7

Test for sulphate:

Answer 7

Add dil. HCl + barium chloride OR barium nitrate.

It should form white ppt. insoluble in acid.

Question 8

Test for nitrate:

Answer 8

Add aluminium powder and excess aq. NaOH. Heat and mix it, then test the gas with:

i) red litmus: turns blue
ii) conc. HCl: forms dense white fumes

Question 9

Test for ammonium:

Answer 9

Adding aq. NaOH: no ppt. If the mixture is warmed, a pungent-smelling gas that turns litmus paper blue will be produced.

Adding aq. NH3: no ppt.

Question 10

Test for calcium:

Answer 10

Adding aq. NaOH: forms white ppt (insoluble in excess).

Adding aq. NH3: no ppt.

Question 11

Test for aluminium:

Answer 11

Add aq. NaOH: forms white ppt. soluble in excess NaOH to form a colourless solution.

Add aq. NH3: forms white ppt. insoluble in excess NH3.

Question 12

Test for zinc:

Answer 12

Adding aq. NaOH: white ppt. forms, soluble in excess NaOH.

Adding aq. NH3: white ppt. forms, soluble in excess NH3 to form a colourless solution.

Question 13

Test for cupric (Cu2+):

Answer 13

Adding aq. NaOH: forms blue ppt., insoluble in excess.

Adding aq. NH3: forms blue ppt., soluble in excess NH3 to form a dark blue solution.

Question 14

Test for ferrous (Fe2+):

Answer 14

Adding aq. NaOH: forms green ppt., insoluble in excess.

Adding aq. NH3: forms green ppt., insoluble in excess.

Question 15

Test for ferric (Fe3+):

Answer 15

Adding aq. NaOH: forms brown ppt., insoluble in excess.

Adding aq. NH3: forms brown ppt., insoluble in excess.