CHEMICAL TESTS

Question 1

Test for halide ions

Answer 1

• add nitric acid
• add silver nitrate solution - then add NH3 to confirm
  Chloride - white precipitate, dissolves in dilute ammonia
  Bromide - cream precipitate, dissolved in concentrated ammonia
  Iodide - yellow precipitate, does not dissolve in ammonia

Question 2

Test for carbonate ions

Answer 2

• add dilute nitric acid
• effervescence and will turn limewater cloudy (due to white calcium carbonate precipitate)
  CO2(g) + Ca(OH)2(aq) ➔ CaCO3(s) + H2O(l)

Question 3

Test for sulfate ions

Answer 3

• add dilute nitric acid
• add barium chloride solution
• white barium sulfate precipitate
  Ba2+(aq) + SO42-(aq) ➔ BaSO4(s)

Question 4

Test for ammonium ions

Answer 4

• add sodium hydroxide to the sample and warm it
• test the gas produced with red litmus (should turn blue)

Question 5

Test for alkene

Answer 5

• add bromine water
• should decolourise

Question 6

Test for primary alcohol

Answer 6

Acidified K2Cr2O7, heat
Orange (Cr2O72-) REDUCED to green (Cr 3+) solution

Question 7

Test for carbonyl

Answer 7

Add 2,4-DNP
- Orange/yellow precipitate forms
- Determine the melting point
- compare melting point to known database values

Question 8

Test for aldehydes

Answer 8

Add tollens reagent and warm gently
Silver mirror forms

Aldehydes are oxidised and silver (I) ions are reduced

Question 9

Test for carboxylic acid

Answer 9

Add sodium carbonate
Carbon dioxide released - effervescence and turns limewater cloudy

Question 10

Test for phenols

Answer 10

Indicator/pH paper turns red / orange OR pH < 7
OR pH meter < 7
AND
No reaction with Na2CO3/CO3 2– /carbonate