8.3 Qualitative Analysis

Question 1

What are qualitative tests?

Answer 1

results are OBSERVATIONS

rather than numerical values.

Question 2

What are the 3 molecules being tested for?

Answer 2

CARBONATES (CO₃^2-)

SULPHATES (SO₄^2-)

HALIDES (X^-)

Question 3

What is the test for carbonates?

Answer 3

carbonate + ACID ⟶ salt + carbon dioxide

acid should not be HCl or H₂SO₄ if later carrying out test for halides/sulfates.

Question 4

During the carbonate test, a positive result is when bubbles of carbon dioxide gas is produced.

How can you test this gas to confirm it is CO₂?

Answer 4

bubble through limewater, (aqueous Ca(OH)₂)

should turn cloudy. (formation of CaCO₃ white precipitate)

Question 5

What is the equation for when carbon dioxide is bubbled through limewater?

Answer 5

CO_{2 (g)} + Ca(OH)_{2 (aq)} ⟶ CaCO_{3 (s)} + H₂O _(l)

Question 6

What does limewater consist of?

Answer 6

aqueous Calcium Hydroxide, Ca(OH)₂

Question 7

What product is formed as a white precipitate during the LIMEWATER test which makes the solution cloudy?

Answer 7

CaCO₃, calcium carbonate

Question 8

What is the test for sulphates?

Answer 8

Sulphate + BARIUM NITRATE (Ba(NO₃)₂) ⟶ Barium sulfate (BaSO₄)

BaSO₄ white precipitate formed.

Barium compound should not be barium chloride if halide test being carried out after.

Question 9

What is the product is formed as a white precipitate during the SULFATE test?

Answer 9

BaSO4, barium sulphate

Question 10

What is the test for halides?

Answer 10

Halide + AgNO₃, SILVER NITRATE ⟶ coloured halide precipitate

Question 11

What different coloured precipitates form for each halide?

Answer 11

chloride - white

bromide - cream

iodide - yellow

Question 12

How can you determine the presence of a silver halide using solubility?

Answer 12

add AQUEOUS AMMONIA to silver halide.

AgCl dissolves in dilute ammonia

AgBr dissolves in concentrated ammonia

AgI insoluble in even concentrated ammonia