20 7 The nitrates of lithium, rubidium and strontium are all white solids. The compounds are held together by ionic bonds. (a) State the meaning of the term ‘ionic bond’. 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(b) What is the percentage by mass of strontium in strontium nitrate? (1) A 38.0 % B 41.4 % C 58.6 % D 74.5 % Turn over 21 (c) These three compounds cannot be identified with certainty from a flame test as the colours seen are similar. Concentrated hydrochloric acid is used in a flame test procedure. (i) Which of the following is a reason for dipping the flame test wire in concentrated hydrochloric acid during a flame test procedure? (1) A it dissolves metal ions from the wire B it neutralises hydroxide ions that might colour the flame C it reduces the metal ions to metal atoms D it reacts with the compounds to form volatile chlorides (ii) The flame colour given by these three solids in the flame test are shades of (1) A green B lilac C red D yellow (iii) What is the best explanation for why metal ions produce different flame colours? (1) Different wavelengths of light energy are A required to promote electrons to higher energy levels B released because electrons move from lower to higher energy levels C released due to different gaps between energy levels D required for electron transfer from non-metal ions to metal ions 22 *(d) Devise a procedure to identify the nitrates of lithium, rubidium and strontium using the effect of heat on the three solids and any precipitation reactions of the compounds. Practical details are not required, but you should give the observations expected in each case. 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(Total for Question 7 = 12 marks) TOTAL FOR PAPER = 80 MARKS 24