OCR A Jun 2017 Paper 1 Q22

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22 This question is about elements from the s-block and p-block of the periodic table. 14 (a) A sample of magnesium is analysed by mass spectrometry. The mass spectrum is shown below. relative abundance (%) 78.99% 10.00% 11.01% 21 22 23 24 25 m / z 26 27 28 29 (i) The species causing the peaks in the mass spectrum are 1+ ions of magnesium. Complete the table to show the number of protons, neutrons and electrons in each 1+ ion of magnesium. protons neutrons electrons m / z 24 25 26 [2] (ii) Calculate the relative atomic mass of the magnesium in the sample. Give your answer to two decimal places. relative atomic mass =[2]<br /> (b) B and C are ionic compounds of two different Group 1 elements. The molar masses of B and C are both approximately 140 g mol1. 15 A student dissolves B and C in water in separate test tubes and analyses the solutions. The observations are shown below. Test Addition of HNO3(aq) followed by BaCl2(aq) Observation B(aq) bubbles no change C(aq) no change white precipitate Use this information and the observations to identify the formulae of B and C. Explain your reasoning.[5]<br /> (c) Fig. 22.1 shows first ionisation energies for elements across Period 3. 16 2500 2000 1500 1000 500 1st ionisation energy / kJ mol1 0 10 11 12 14 15 13 Atomic number, Z 16 17 18 Fig. 22.1 (i) Add a point to Fig. 22.1 for the first ionisation energy of the element with Z = 10. [1] (ii) Estimate the energy required to form one Na+(g) ion from one Na(g) atom. Give your answer in kJ, in standard form, and to two significant figures. (iii) Explain why the first ionisation energies in Fig. 22.1 show a general increase across Period 3 (NaAr). energy =kJ [1][3]<br /> (iv) Explain why the general increase in first ionisation energies across Period 3 is not followed for Mg (Z = 12) to Al (Z = 13). 17[2]<br />

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