Qualitative analysis

Question 1

test for carbonate ions (CO3^2-) and equation

Answer 1

• add acid to test tube containing limewater and the carbonate solution , this releases CO2, turning limewater cloudy
• 2H+(aq) + CO3^2-(aq) —> H2O(l) + CO2(g)

Question 2

test for ammonium ions (NH4^+) and equation

Answer 2

• add warm NaOH which will form NH3 gas and water
• NH4+(aq) + OH-(aq) —> NH3(g) + H2O(l)

Question 3

test for ammonia gas

Answer 3

turns damp red litmus paper blue

Question 4

test for sulfate ions (SO4^2-)

Answer 4

add BaCl2 to form BaSO4 which is an insoluble ppt

Question 5

what’s the order in which ions are tested

Answer 5

• CSH

Question 6

why are carbonates tested for first

Answer 6

• carbonate test: neither sulfate nor halide ions produce bubbles with dilute acid, so a +ve test confirms CO3^2- present

Question 7

why are sulfates tested for after carbonates

Answer 7

• sufate test: BaCO3 is white and insoluble too, so can produce a false +ve on addition of BaCl2 for sulfate test if carbonate ions aren’t confirmed and removed first

Question 8

why are halides tested for after sulfates

Answer 8

• silver carconate (Ag2CO3) and silver sulfate (Ag2SO4) are both insoluble in water so will produce ppts for the halide test.