Core Practicals/tests

Question 1

How do you separate a solvent from a solution using simple distillation?

Answer 1

• Heat solution → solvent evaporates. • Vapour enters condenser → cools → becomes liquid. • Collect the solvent separately. • Separates solvent from solute.

Question 2

How do you separate dyes in ink using chromatography?

Answer 2

• Draw pencil baseline; place ink spots on it. • Stand paper in solvent (below baseline). • Solvent rises carrying dyes. • More soluble dyes travel further. • Rf = distance travelled by spot ÷ distance travelled by solvent.

Question 3

How do you investigate pH change when adding CaO or Ca(OH)₂ to hydrochloric acid?

Answer 3

• Add fixed volume of dilute HCl to beaker. • Add CaO or Ca(OH)₂ in small portions. • Stir after each addition. • Measure pH each time. • pH rises as acid neutralises. • CaO reacts faster.

Question 4

How do you make hydrated copper sulfate crystals?

Answer 4

• Warm dilute sulfuric acid gently. • Add excess copper oxide. • Stir until no more reacts. • Filter to remove unreacted solid. • Heat filtrate gently to concentrate. • Leave to cool → crystals form. • Dry with filter paper.

Question 5

What happens during electrolysis of copper sulfate with inert electrodes?

Answer 5

• Cathode: Cu²⁺ + 2e⁻ → Cu (pink coating). • Anode: oxygen released from OH⁻. • Solution becomes paler as Cu²⁺ decreases.

Question 6

What happens during electrolysis of copper sulfate with copper electrodes?

Answer 6

• Cathode gains mass (Cu deposits). • Anode loses mass (Cu dissolves → Cu²⁺). • Demonstrates copper purification.

Question 7

How do you perform an accurate acid–alkali titration?

Answer 7

• Pipette alkali into conical flask. • Add indicator. • Fill burette with acid. • Add acid slowly while swirling. • Stop at end-point colour change. • Repeat for concordant titres. • Use volumes to calculate concentration.

Question 8

How do you measure rate of reaction by gas production?

Answer 8

• React marble chips with hydrochloric acid. • Collect gas in gas syringe. • Record volume at intervals. • Faster with higher temp/concentration or smaller chips.

Question 9

How do you measure rate of reaction by colour change?

Answer 9

• Mix sodium thiosulfate with hydrochloric acid. • Time how long until cross disappears. • Higher temperature → faster rate.

Question 10

How do you identify metal ions using flame tests?

Answer 10

• Li⁺ red • Na⁺ yellow • K⁺ lilac • Ca²⁺ orange-red • Cu²⁺ blue-green

Question 11

How do you identify metal ions using sodium hydroxide solution?

Answer 11

• Al³⁺ white ppt → dissolves in excess • Ca²⁺ white ppt • Mg²⁺ white ppt • Cu²⁺ blue ppt • Fe²⁺ green ppt • Fe³⁺ brown ppt

Question 12

How do you test for carbonate ions?

Answer 12

• Add acid. • Look for fizzing (CO₂). • Confirm CO₂ with limewater → cloudy.

Question 13

How do you test for sulfate ions?

Answer 13

• Add dilute HCl. • Add barium chloride. • White precipitate = sulfate.

Question 14

How do you test for halide ions?

Answer 14

• Add nitric acid. • Add silver nitrate. • Cl⁻ white ppt • Br⁻ cream ppt • I⁻ yellow ppt

Question 15

How do you investigate the temperature rise when alcohols burn?

Answer 15

• Burn alcohol under water beaker. • Measure water temp before/after. • Weigh burner before/after. • Keep distance, wick length, water volume constant. • Calculate Q = mcΔT. • Larger alcohols release more energy per mole.