QA

Question 1

State the cations in NaOH

Answer 1

Calcium (Ca2+) WHITE ppt, INSOLUBLE in excess (Calcium hydroxide)

Lead (Pb2+) WHITE ppt, dissolves in excess (colourless solution)

Aluminium (Al3+) WHITE ppt, dissolves in excess (colourless solution)

Zinc (Zn2+) WHITE ppt, dissolves in excess (colourless solution)

Iron (Fe2+) GREEN ppt, insoluble in excess

Iron (Fe3+) REDDISH-BROWN ppt, insoluble in excess

Copper (Cu2+) BLUE ppt, insoluble in excess

Ammonium (NH4+) NO VISIBLE REACTION, EFFERVESCENCE observed, AMMONIA gas produced

Question 2

State the cations in aqueous NH3

Answer 2

Calcium (Ca2+) No visible reaction

Lead (Pb2+) WHITE ppt, insoluble in excess

Aluminium (Al3+) WHITE ppt, insoluble in excess

Zinc (Zn2+) WHITE ppt, dissolves in excess (colourless solution)

Iron (Fe2+) GREEN ppt, insoluble in excess (slowly turns brown left standing)

Iron (Fe3+) REDDISH-BROWN ppt, insoluble in excess

Copper (Cu2+) BLUE ppt, dissolves in excess , forms dark blue solution

Ammonium (NH4+) No visible reaction

Question 3

State the anion tests

Answer 3

Nitrate (NO³-) Add NaOH, add ALUMINIUM foil, WARM mixture, test gas with damp red litmus
+ve Effervescence observed, gas evolved turns damp red litmus blue,(NH3 produced)

Carbonate (CO³-) Add HCl, Bubble gas into limewater
+ve Effervescence observed, forms white ppt in lime water (CO2 present)

THOSE THAT HNO3 AND BARIUM/LEAD nitrate or SILVER/LEAD nitrate
(Prevent precipitation of insoluble metal carbonates)

Sulfate (SO4-) Add HNO3, add Ba(NO³)2 or Pb(NO³)2, (This prevents formation of BaCO³ or PbCO³)
+ve White ppt, BaSO⁴/ PbSO⁴

Chloride (Cl-) Add Add HNO³, add Ag(NO³)2 or Pb(NO³)2, (This prevents formation of AgCO³ or PbCO³)
+ve White ppt, AgCl, PbCl

Iodide (I-) Add HNO³, add Ag(NO³)2 or Pb(NO3)2, (This prevents formation of AgCO³ or PbCO³)
+ve Yellow ppt, AgI, PbI

Question 4

Why is HNO3 added to the various anion tests?

Answer 4

HNO3 added to Cl-, SO4-, I- tests for prevention precipitation of insoluble metal carbonates

Question 5

State the gas tests

Answer 5

Hydrogen Place burning splint at mouth of test tube
(neutral, colourless, odourless)
+ve: Burning splint extinguished with ‘pop’ sound

Oxygen Place glowing splint at mouth of test tube
(neutral, colourless, odourless)
+ve: Glowing splint relights

Carbon Dioxide Bubble gas through limewater
(acidic, colourless odourless)
+ve: White ppt in limewater

Chlorine Place a damp blue litmus
(acidic, greenish yellow, pungent)
+ve: Damp blue litmus turns red then is bleached

Sulfur dioxide Place a drop of KMnO4 on piece of filter paper, then at mouth of test tube
(acidic, colourless, pungent)
+ve: KMnO4 turns from purple to colourless

Ammonia Place a piece of damp red litmus at mouth of test tube
(alkaline, colourless, pungent)
+ve: NH3 turns damp red litmus blue