2811_Jan_03MS - Subject Chemistry Foundation Code 2811...

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Page 1 of 8 Subject: Chemistry Foundation Code: 2811 Session: January Year: 2003 Final Mark Scheme 25/1/2003 MAXIMUM MARK 60
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Page 3 of 8 Abbreviations, annotations and conventions used in the Mark Scheme / = alternative and acceptable answers for the same marking point ; = separates marking points NOT = answers which are not worthy of credit ( ) = words which are not essential to gain credit = (underlining) key words which must be used to gain credit ecf = error carried forward AW = alternative wording ora = or reverse argument 1. (a) number of isotope protons neutrons electrons 69 Ga 31 38 31 71 Ga 31 40 31 [2] (b) deflection/ deflector 9 ignore ‘what deflects’ detection/ detector 9 acceleration/ accelerator 9 ignore ‘atoms’ beyond 1st stage ionisation/ electron bombardment/ ioniser 9 not electron gun [4] (c) (i) average mass/weighted mean/average mass of an atom / the isotopes 9 compared with carbon-12 9 1/12th of mass of carbon-12 / on a scale where carbon-12 is 12 9 not 12 g or... mass of 1 mole of atoms 9 compared with carbon-12 9 1/12th of mass of 1 mol of carbon-12 / on a scale where carbon-12 is 12 g 9 [3] (ii) 69 Ga: 61%; 71 Ga: 39% 9 ( allow 62/38 → 69.76 below) [1] (iii) A r = 69 x 61/100 + 71 x 39/100 = 69.78 9 = 69.8 9 ignore g / grammes [2] [Total: 12 marks] 9 9
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