1. 1
   Iron(III) ions are responsible for the orange-brown colour of rust stains. One of these ions can be represented by the nuclear symbol $^{56}_{26}\mathrm{Fe}^{3+}$.

   (a)

   How many electrons does this ion contain?

   [1 mark]

   • A23
   • B26
   • C29
   • D56

   (b)

   How many neutrons does this ion contain?

   [1 mark]

   • A26
   • B56
   • C33
   • D30

   (c)

   A different species contains 26 protons, 32 neutrons and 24 electrons. Deduce its nuclear symbol and state, with a reason, how its atoms are related to atoms of the iron in $^{56}_{26}\mathrm{Fe}^{3+}$.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In 1909 a team fired a beam of positively charged alpha particles at a sheet of gold foil only a few hundred atoms thick. Almost all of the alpha particles passed straight through with little or no deflection, a small fraction were deflected through large angles, and roughly 1 in 8000 bounced back towards the source. A gold nucleus has a radius of about 7 × 10⁻¹⁵ m, while a gold atom has a radius of about 1.4 × 10⁻¹⁰ m.

   (a)

   Which observation shows that most of the volume of an atom is empty space?

   [1 mark]

   • ASome alpha particles bounced back
   • BAlmost all alpha particles passed straight through
   • CSome alpha particles were deflected through large angles
   • DThe alpha particles are positively charged

   (b)

   Which conclusion is best supported by the very rare rebounds?

   [1 mark]

   • AElectrons are spread evenly through the atom
   • BAtoms contain neutral neutrons
   • CThe nucleus is small, dense and positively charged
   • DThe electrons are located in the nucleus

   (c)

   Determine the ratio of the radius of a gold atom to the radius of its nucleus, and comment on what this shows about how mass is distributed in the atom.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A geochemistry laboratory analyses isotopes. Gallium consists of two isotopes: gallium-69, relative isotopic mass 68.926, abundance 60.11 %, and gallium-71, relative isotopic mass 70.925, abundance 39.89 %. Boron consists of boron-10 and boron-11, with relative isotopic masses that may be taken as 10.0 and 11.0. The accepted relative atomic mass of boron is 10.81, but boron extracted from a sample of the mineral tourmaline gives a relative atomic mass of 10.84.

   (a)

   Calculate the relative atomic mass of gallium to two decimal places, and explain why it is closer to 69 than to 71.

   [3 marks]

   (b)

   Determine the percentage abundances of the two boron isotopes in the tourmaline sample, and compare the sample with boron of the accepted relative atomic mass.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Hydrogen has three isotopes: protium (hydrogen-1), deuterium (hydrogen-2) and tritium (hydrogen-3). Heavy water, D₂O, is made from deuterium and is used in some nuclear reactors. Heavy water has a density of 1.11 g cm⁻³ compared with 1.00 g cm⁻³ for ordinary water, and it boils at 101.4 °C. Heavy water reacts with sodium in the same way as ordinary water, producing a gas and an alkaline solution. Relative isotopic masses: hydrogen-1 = 1.0078, deuterium = 2.0141, oxygen-16 = 15.995.

   (a)

   Deduce the numbers of protons, neutrons and electrons in atoms of each of the three hydrogen isotopes and in the ion $^{2}_{1}\mathrm{H}^{+}$, and explain why heavy water and ordinary water react in the same way with sodium.

   [6 marks]

   (b)

   Using the relative isotopic masses, evaluate the hypothesis that the difference in density between heavy water and ordinary water is caused only by the greater mass of the deuterium nucleus.

   [6 marks]

   Total for question 4: 12 marks

End of questions