Chapter 1 Practice Paper: Experimental Chemistry and Purification — question paper

Section A: Multiple-choice questions[10 marks]

Choose the one correct answer for each question.

1. 1

   Which apparatus measures exactly 25.0 cm³ of a solution most precisely?

   1. Aa 100 cm³ measuring cylinder
   2. Ba 25 cm³ pipette
   3. Ca 100 cm³ beaker
   4. Da gas syringe
   ( )
2. 2

   A student needs the total volume of gas made in a slow reaction, measured every minute. The best piece of apparatus is

   1. Aa gas syringe
   2. Ba burette
   3. Ca pipette
   4. Da conical flask
   ( )
3. 3

   Sand is mixed with copper(II) sulfate solution. The sand is removed by

   1. Aevaporation, leaving the sand behind
   2. Bfractional distillation, collecting the sand
   3. Cfiltration, leaving the solution as filtrate
   4. Dchromatography, separating the sand spot
   ( )
4. 4

   Pure water boils at exactly 100 °C at laboratory pressure. A sample boils over the range 102–106 °C. The sample is

   1. Apure water at high pressure
   2. Ba mixture of water and ethanol
   3. Cwater that has been distilled
   4. Da solution of solid in water
   ( )
5. 5

   A chromatogram of a sweetener shows one spot matching a known banned dye after the same running time. The safest conclusion is that the sweetener

   1. Acontains that dye
   2. Bcontains only that dye
   3. Cis a pure substance
   4. Dhas no colouring at all
   ( )

Section B: Structured questions[20 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 student makes hydrogen by adding dilute acid to zinc and needs to collect the gas produced.

   1. (a)

      Name a suitable piece of apparatus for measuring the total volume of hydrogen collected.

      [1]
   2. (b)

      Hydrogen is much less dense than air and only very slightly soluble in water. Describe how the gas can be collected if a gas syringe is not available.

      [2]
   3. (c)

      State one safety precaution for this experiment and say what it protects against.

      [1]
2. 2

   A mixture contains salt dissolved in water with traces of insoluble grit.

   1. (a)

      Name the first separation step and the property of the grit that makes it work.

      [2]
   2. (b)

      Describe how pure, well-formed salt crystals are then obtained from the filtrate.

      [4]
3. 3

   Two colourless liquids, propan-1-ol (boiling point 97 °C) and water (boiling point 100 °C), are miscible. A student wants to separate them.

   1. (a)

      Name the separation technique that should be used.

      [1]
   2. (b)

      Explain why simple distillation alone would give a poor separation of these two liquids.

      [2]
   3. (c)

      State and explain which liquid distils first.

      [2]
4. 4

   Substance X melts sharply at 80.2 °C. Substance Y melts slowly over the range 76–81 °C. Both samples look identical.

   1. (a)

      Which sample is purer? Explain your answer using the melting data.

      [2]
   2. (b)

      The identity of X can be checked against a data table. State one other measurement, besides melting point, that could confirm the identity of X.

      [1]
   3. (c)

      Y is thought to be X mixed with a little impurity. Using the data, state how the melting behaviour of Y differs from pure X in two ways.

      [2]