WA1 Practice Paper: Weighted Assessment 1 — question paper

Section A: Multiple-choice questions[10 marks]

Answer all questions. For each question, write the letter (A, B, C or D) of the correct answer.

1. 1

   Pure water is obtained from a solution of salt in water by

   1. Afiltration
   2. Bevaporation
   3. Cpaper chromatography
   4. Dsimple distillation
   ( )
2. 2

   On a chromatogram, dye X moves 6.2 cm while the solvent front moves 8.0 cm. Which statement about the Rf value of X is correct?

   1. AIt changes if the solvent is allowed to travel further.
   2. BIt is 6.2 ÷ 8.0 = 0.775.
   3. CIt is measured in cm.
   4. DIt would be lower in a solvent that dissolves X better.
   ( )
3. 3

   A pure solid is heated steadily. Its temperature rises, then stays constant for several minutes, then rises again. The constant-temperature region shows the solid is

   1. Amelting at a fixed melting point
   2. Bboiling at a fixed boiling point
   3. Creacting with the air
   4. Dalready a liquid throughout
   ( )
4. 4

   Ammonia gas is soluble in water and less dense than air. It is collected by

   1. Acollection over water
   2. Bupward delivery of air
   3. Cdownward delivery of air
   4. Da gas syringe only
   ( )
5. 5

   During melting, the particles of a substance

   1. Again energy and vibrate faster about fixed positions
   2. Bgain energy and move further apart as fixed positions are lost
   3. Close energy and move closer together
   4. Dgain energy and separate completely at random
   ( )
6. 6

   Equal amounts of four gases are released at one end of a long tube at the same temperature. Which reaches the far end first?

   1. Ahydrogen, Mr = 2
   2. Bammonia, Mr = 17
   3. Coxygen, Mr = 32
   4. Dcarbon dioxide, Mr = 44
   ( )
7. 7

   On a cooling curve of a pure liquid, the temperature stays constant while the liquid freezes because

   1. Ano heat is being lost to the surroundings
   2. Bthe particles have stopped moving
   3. Cheat lost is balanced by heat given out as particles settle into the lattice
   4. Dthe thermometer is not working
   ( )
8. 8

   Bromine vapour spreads slowly through a jar of air while hydrogen spreads quickly. This is because at the same temperature bromine molecules

   1. Aare larger in number
   2. Bhave a lower average speed
   3. Chave more kinetic energy each
   4. Dcollide with no air particles
   ( )
9. 9

   Which statement about paper chromatography is correct?

   1. AThe start line is drawn in ink so it is clearly visible.
   2. BThe solvent level starts above the start line.
   3. CA pure dye always gives two spots on the final chromatogram.
   4. DDyes with higher Rf values are less attracted to the paper.
   ( )
10. 10

    Which difference between boiling and evaporation of a liquid is correct?

    1. ABoiling happens at a fixed temperature throughout the liquid; evaporation happens at any temperature at the surface only.
    2. BBoiling happens only at the surface; evaporation happens throughout.
    3. CBoiling happens below the melting point; evaporation happens above it.
    4. DThere is no difference between the two processes.
    ( )

Section B: Structured questions[30 marks]

Answer all questions in the spaces provided. Show all necessary working. Give numerical answers to 3 significant figures where appropriate, with units.

1. 1

   A mixture contains sand, which is insoluble, and common salt (sodium chloride), which is soluble in water.

   1. (a)

      Describe how a dry sample of the sand is separated from the mixture.

      [3]
   2. (b)

      Describe how crystals of salt are then obtained from the filtrate.

      [2]
2. 2

   A student investigates a black ink using paper chromatography.

   1. (a)

      Describe how the chromatogram is obtained, including two precautions that make the results reliable.

      [4]
   2. (b)

      The finished chromatogram shows three separate coloured spots. State what this shows about the ink.

      [1]
3. 3

   A sealed container holds a fixed amount of carbon dioxide gas at room temperature.

   1. (a)

      Describe the arrangement, separation and motion of the carbon dioxide particles inside the container.

      [3]
   2. (b)

      The container is cooled. Use the kinetic particle theory to explain what happens to the pressure of the gas.

      [3]
4. 4

   A long glass tube has a plug of cotton wool soaked in hydrochloric acid at one end and a plug soaked in aqueous ammonia at the other end, inserted at the same time. After a few minutes a white ring forms inside the tube, closer to the hydrochloric acid end.

   1. (a)

      Name the white substance and write the equation for its formation.

      [2]
   2. (b)

      Explain why the ring forms closer to the hydrochloric acid end.

      [3]
   3. (c)

      State and explain the effect of warming the tube on how quickly the white ring forms.

      [2]
5. 5

   Samples of two colourless liquids are investigated. Liquid L boils at a single steady temperature of 100 °C at standard atmospheric pressure. Liquid M is a mixture of ethanol (boiling point 78 °C) and water.

   1. (a)

      State what the boiling behaviour of L suggests about its purity, and why.

      [2]
   2. (b)

      A sample of solid N melts gradually over the range 48–52 °C. Predict the melting point of the pure substance that N contains, and explain your answer.

      [2]
   3. (c)

      Describe how the ethanol is obtained as a separate liquid from mixture M.

      [3]