chemical tests

Question 1

test for alcohols

Answer 1

• add 1 cm3 of alcohol to a test tube and add a small piece of sodium
• presence of alcohol is indicated by a white precipitate and effervescence

Question 2

how to test for different types of alcohols

Answer 2

• heat under reflux with acidified potassium dichromate (K₂Cr₂O₇)
• primary and secondary will be oxidised and show a colour change from orange to green
  -tertiary alcohols cant be oxidised so they will remain orange

Question 3

test for aldehydes and ketones

Answer 3

• tollens reagent:
  Aldehyde: Silver mirror
  Ketone: No change
• Fehling’s solution:
  Aldehyde: Blue to brick-red precipitate
  Ketone: No change

Question 4

test for alkenes

Answer 4

• add bromine water to sample
• if an alkene is present the bromine water will turn colourless

Question 5

test for carboxylic acids

Answer 5

add Na₂CO₃ to the sample
- if the carboxylic acid is present CO₂ will be given off

Question 6

test for haloalkane

Answer 6

add silver nitrate (AgNO₃
- Cl = white ppt
Br = cream ppt
I = yellow ppt

Question 7

test for cations (NH₃+)

Answer 7

• Add sodium hydroxide and gently warm.
• Test gas with damp red litmus paper → turns blue (ammonia is alkaline).

Question 8

Tests for Group 2 cations (e.g., Mg²⁺, Ca²⁺, Ba²⁺):

Answer 8

• Add sodium hydroxide dropwise:
• Mg²⁺ forms a white precipitate.
• Ca²⁺ and Ba²⁺ may form slight white precipitates (Ba²⁺ may remain colourless).

Flame tests:
Calcium: Brick red
Strontium: Red
Barium: Pale green

Question 9

test for Transition Metal Ions (with NaOH):

Answer 9

Fe²⁺: Green precipitate (turns brown in air)
Fe³⁺: Brown precipitate
Cu²⁺: Blue precipitate

Question 10

test for Carbonate (CO₃²⁻):

Answer 10

• Add dilute acid → effervescence (CO₂ gas).
• Bubble gas through limewater → turns cloudy.

Question 11

test for Sulfate (SO₄²⁻):

Answer 11

• Add dilute HCl (or nitric acid) and then barium chloride solution.
• White precipitate of barium sulfate.

Question 12

Test for carboxylic acids:

Answer 12

Add sodium carbonate → effervescence (CO₂ gas).

Question 13

Flame Tests for Metal Ions

Answer 13

Li⁺: Crimson red
Na⁺: Yellow
K⁺: Lilac
Ca²⁺: Brick red
Ba²⁺: Pale green
Cu²⁺: Blue-green

Question 14

test to distinguish between MgCl₂ and AlCl₃

Answer 14

reagent: NaOH or a group 1 hydroxide
observation with MgCl₂: white ppt
observation with AlCl₃: white ppt which dissolves in excess NaOH

or
reagent: group 1 carbonate
observation with MgCl₂: white ppt
observation with AlCl₃: white ppt and effervescence

Question 15

How do you test for sulfate ions (SO₄²⁻)?

Answer 15

Add dilute hydrochloric acid (HCl) followed by barium chloride (BaCl₂).
A white precipitate forms