1. 1
   A student sets up two identical beakers of still water at the same depth, one at 20°C and one at 60°C. At the same moment, one drop of purple food dye is added carefully to the surface of each beaker, without any stirring, and the student times how long it takes for the purple colour to spread through each beaker.

   (a)

   What causes the purple colour to spread through the water without any stirring?

   [1 mark]

   • AParticles of dye and water are in continuous random motion and mix together (diffusion)
   • BThe dye is denser than water and sinks to spread out through the beaker
   • CConvection currents force the dye downward and around the beaker
   • DThe dye reacts chemically with the water molecules

   (b)

   Which beaker would you expect to show the purple colour spreading fastest, and why?

   [1 mark]

   • AThe 20°C beaker, because particles move faster when they are cold
   • BThe 60°C beaker, because its particles have more kinetic energy and move faster, colliding and mixing more quickly
   • CBoth beakers at exactly the same rate, because temperature does not affect diffusion
   • DThe 60°C beaker, because heat makes the dye chemically more soluble in water

   (c)

   Explain, in terms of particles, why the purple colour eventually spreads evenly throughout the water in both beakers.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A technician is given three labelled samples to check: a small bar of pure silicon used in electronics, a sample of brass (a mixture of copper and zinc), and a jar of pure sulfur powder.

   (a)

   Which of the three samples are elements?

   [1 mark]

   • ASilicon and brass only
   • BBrass and sulfur only
   • CSilicon and sulfur only
   • DAll three samples

   (b)

   Why is brass not classified as an element?

   [1 mark]

   • AIt is a compound formed from carbon and zinc
   • BIt has no chemical symbol
   • CIt cannot conduct electricity
   • DIt is made from atoms of two different elements (copper and zinc) mixed together, not just one type of atom

   (c)

   State what is meant by an element, and explain why pure silicon and pure sulfur are both classified as elements.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Bromine occurs naturally as a mixture of two isotopes, bromine-79 and bromine-81, present in roughly equal proportions. The relative atomic mass of bromine given in data tables is 79.9. Bromine has atomic number 35.

   (a)

   Define the term isotope, and state the number of protons and the number of neutrons in one atom of bromine-81.

   [3 marks]

   (b)

   Explain why the relative atomic mass of bromine (79.9) is close to, but not exactly, the simple average of the mass numbers of its two isotopes, and explain why it does not have to be a whole number.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Silicon has atomic number 14 and phosphorus has atomic number 15. Both elements are found next to each other in Period 3 of the periodic table, and argon, later in the same period, has atomic number 18.

   (a)

   Describe the electronic structure of an atom of silicon and an atom of phosphorus, and explain how their positions in the periodic table relate to these electronic structures.

   [6 marks]

   (b)

   Silicon and phosphorus are both non-metals, but argon, later in the same period, is a noble gas and extremely unreactive. Explain, in terms of electronic structure, why argon is so much less reactive than silicon and phosphorus.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   An engineering company casts molten aluminium, poured as a liquid at high temperature, into moulds, where it cools and solidifies into solid aluminium ingots. Later, some ingots are remelted so the metal can be reused.

   (a)

   When the molten aluminium cools and solidifies in the mould, what happens to the arrangement and movement of its particles?

   [1 mark]

   • AThe particles come closer together, become arranged in a more ordered pattern, and vibrate about fixed positions
   • BThe particles move further apart from each other and move more randomly
   • CThe particles stop moving and vibrating completely
   • DThe particles gain energy and move faster

   (b)

   What happens to the energy of the aluminium as it changes from liquid to solid?

   [1 mark]

   • ANo energy change occurs during a change of state
   • BEnergy is transferred from the aluminium to the surroundings (the aluminium loses energy)
   • CEnergy is transferred from the surroundings to the aluminium
   • DThe aluminium gains energy and its temperature rises

   (c)

   Explain why the temperature of the aluminium does not fall while it is solidifying, even though it is continuing to lose energy to the surroundings.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   An atom of an unknown element X has 20 protons and a mass number of 40. A second atom, of element Y, has 19 protons and 20 neutrons.

   (a)

   How many electrons does an atom of element X have?

   [1 mark]

   • A40
   • B18
   • C20
   • D60

   (b)

   What is the mass number of element Y?

   [1 mark]

   • A19
   • B20
   • C1
   • D39

   (c)

   Identify which elements X and Y are likely to be, giving a reason for each identification.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A school data book lists the relative masses of the three sub-atomic particles found in atoms: protons, neutrons and electrons. Two isotopes of neon, neon-20 and neon-22, are also listed, both with atomic number 10.

   (a)

   State the relative mass of a proton, a neutron and an electron, and explain why the mass of an atom is considered to come almost entirely from its protons and neutrons rather than its electrons.

   [3 marks]

   (b)

   Explain, in terms of sub-atomic particles, why neon-20 and neon-22 have different masses but identical chemical properties.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A student examines four elements with atomic numbers 4, 12, 20 and 38 — beryllium, magnesium, calcium and strontium — all found in the same column of the periodic table.

   (a)

   Explain, in terms of electronic structure, why these four elements are placed in the same group of the periodic table, and describe how their position within the table changes going down the group.

   [6 marks]

   (b)

   Explain why the periodic table is described as showing “periodicity”, using these four elements and their neighbours as an example.

   [6 marks]

   Total for question 8: 12 marks

End of questions