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Paper 6 style practice paper: Alternative to practical — mark scheme

QuizQuipPractice Series
QQ/IGCSE-CHEM/P6S

IGCSE · Cambridge IGCSE Chemistry (Extended)

Mark scheme

Alternative to practical

Paper 6 style practice paper · Maximum mark: 30

Notes for markers

  • Award one mark for each point marked [1], up to the marks shown for the part.
  • Accept answers worded differently that show the same understanding.
  • Units are required where the answer line shows one. ecf: allow an error carried forward.

Section A: Experimental techniques[15 marks]

QuestionAnswer and marking pointsMarks
1(a)

The indicator changes from red to yellow. [1]

1
1(b)

So that parallax error is avoided and the volume recorded is accurate.

  • avoids parallax error / gives an accurate reading [1]
1
1(c)

Titrations 1 and 2 give 22.50 cm³ and 22.50 cm³, which are concordant within 0.10 cm³. Titration 3 gives 24.55 cm³, which is more than 0.10 cm³ away, so it is not concordant. The average of the concordant titres is 22.50 cm³.

  • selects the concordant titres (within 0.10 cm³) [1]
  • average = 22.50 cm³ [1]
2
Total for Question 14
2(a)

carbon dioxide [1]

1
2(b)

The carbonate ion, CO₃²⁻. [1]

1
2(c)

Hold a lighted splint to the gas; it burns with a squeaky pop.

  • lighted splint gives a squeaky pop [1]
1
2(d)

Acidify the solution with dilute nitric acid, then add aqueous barium nitrate; a white precipitate forms.

  • acidify with dilute nitric acid, then add barium nitrate → white precipitate [1]
1
Total for Question 24
3(a)

Rf = distance moved by the dye ÷ distance moved by the solvent = 6.0 ÷ 8.0 = 0.75.

  • Rf = distance moved by dye ÷ distance moved by solvent [1]
  • 0.75 [1]
2
3(b)

The colouring is a mixture of two dyes. [1]

1
3(c)

Ink is soluble in the solvent, so it would run up the paper and spoil the chromatogram.

  • ink would dissolve and run in the solvent [1]
1
Total for Question 34
4(a)

filtration [1]

1
4(b)

Crystallisation, or evaporation to the point of crystallisation.

  • crystallisation / evaporation [1]
1
4(c)

Measure its melting point; a pure salt melts sharply at one temperature.

  • sharp melting point [1]
1
Total for Question 43

Section B: Observations, analysis and planning[15 marks]

QuestionAnswer and marking pointsMarks
5(a)

gas syringe [1]

1
5(b)

The mass and size of the marble chips, and the temperature of the acid.

  • mass / size of the marble chips [1]
  • temperature of the acid [1]
2
5(c)

The volume–time graph for the more concentrated acid has a steeper start, so the same final volume of gas is collected in a shorter time.

  • steeper gradient / reaches the final volume sooner [1]
  • the same final volume of gas is collected in both experiments [1]
2
Total for Question 55
6(a)

The blue crystals turn white, and colourless droplets of water condense on the cooler part of the test tube.

  • blue crystals turn white [1]
  • droplets of water / condensation form [1]
2
6(b)

The water of crystallisation is driven off, so the hydrated salt breaks down into anhydrous copper(II) sulfate and water.

  • water of crystallisation is driven off [1]
  • the blue solid becomes anhydrous copper(II) sulfate [1]
2
6(c)

Hold the test tube with tongs and point its mouth away from people, and wear eye protection.

  • point the tube away from people / use tongs or eye protection [1]
1
Total for Question 65
7(a)

Chloride, Cl⁻. [1]

1
7(b)

Copper(II), Cu²⁺. [1]

1
7(c)

The blue precipitate dissolves to give a deep blue solution. [1]

1
7(d)

Acidify Z with dilute nitric acid, then add aqueous barium nitrate; no white precipitate would form.

  • acidify with dilute nitric acid, then add barium nitrate [1]
  • no white precipitate / no observable change [1]
2
Total for Question 75

— End of mark scheme —