6 (B410U10-1) Examiner only 10. (a) Some students were discussing ionisation energies. (i) State the meaning of the term standard molar first ionisation energy. [2] (ii) The graph below shows the logarithm of the first eight successive ionisation energies for element X. © WJEC CBAC Ltd. 0 0 2.0 3.0 4.0 5.0 2 4 6 1 3 5 7 8 Number of electron lost log10 (Ionisation energy) I. Explain why successive ionisation energies increase. [2] II. Use the graph to determine in which group of the Periodic Table element X is found. Explain your answer. [2] (B410U10-1) Turn over. B 410 U101 07 7 Examiner only (b) The students used a hydrogen discharge tube and observed some coloured lines. One said that these visible lines could be used to determine the value of the first ionisation energy of hydrogen. (i) Discuss whether you agree with this student’s suggestion. You should include an explanation of how spectral lines are produced and how they can be used to determine ionisation energy. [6 QER] (ii) A spectral line with a frequency of 3.28 × 1015 Hz was formed when an atom of hydrogen was ionised. Calculate the first ionisation energy of hydrogen in kJ mol−1. Give your answer to the appropriate number of significant figures. [3] Ionisation energy = ................................................ kJ mol−1 © WJEC CBAC Ltd. 15 8 (B410U10-1) Examiner only 11. (a) When acids are being used chemists often refer to the pH of the solution. (i) State what is meant by pH. [1] (ii) Calculate the pH of 0.50 mol dm−3 hydrochloric acid. [1] pH = ................................................ (iii) Explain the observation that the pH of 0.10 mol dm−3 ethanoic acid, CH3COOH, is higher than the pH of 0.10 mol dm−3 hydrochloric acid. [3] (b) Water is able to act as a base as it can accept H+ to form H3O+. (i) Draw a dot and cross diagram to show the arrangement of electrons in H3O+. Show outer electrons only. [2] (ii) Name the type of bond present between H2O and the H+ added to form H3O+. [1] ............................................................................................................................................. (iii) Suggest a value for the bond angle between the O—H bonds in H3O+. Explain your answer. [3] © WJEC CBAC Ltd. (B410U10-1) Turn over. 9 Examiner only (c) An equilibrium exists, in aqueous solution, between chromate(VI) ions, CrO4 2−, and dichromate(VI) ions, Cr2O7 2−. 2CrO4 2−(aq) + 2H+(aq) a Cr2O7 2−(aq) + H2O(l) yellow orange (i) State le Chatelier’s principle. [2] (ii) Describe what is seen when aqueous sodium hydroxide is added to an orange solution containing dichromate(VI) ions. Explain your answer. [2] © WJEC CBAC Ltd. 15