Qualitative Analysis

Question 1

Test for carbonates

Answer 1

• tests for Co3 2- ions
• add strong acid eg: HNO3 - not Hal as it would introduce cl- ions
• collect gas produced and pass through lime water
• positive result: fizzing + limewater turns cloudy
  Co3 2- + 2H+ -> H2O + CO2

Question 2

Test for sulphates

Answer 2

• test for So4 2-
• dilute HCL and barium chloride (BaCl2 )
• forms a white precipitate of barium sulphate which is insoluble
  Ba2+ (aq) + So4 2- (aq) -> BaSo4 (s)

Question 3

Test for Halide ion

Answer 3

• tests for cl- , Br- , I-
• add acidified AgNO3 (HNo3)
• do not use hcl as would introduce cl- ions
• forms white , cream or yellow precipitate going down group
• cl- soluble in dilute ammonia
• br- soluble in conc ammonia
• I- not soluble in ammonia

Ag + + Cl- -> AgCl

Question 4

Test for ammonium

Answer 4

• test for NH4 +
• add NaOH and warm it
• test gas produced with red litmus paper
• positive result is red litmus paper turns blue as NH3 gas is produced and is alkaline

NH4+ + OH- -> NH3 + H2O

Question 5

What is the correct test order

Answer 5

1. Carbonate
2. Sulphate
3. Halide
4. Ammonium
   Barium chloride reacts with co3 2- to form Baco3 which forms a precipitate
   Silver reacts with sulphate to form AgSO4