Tin reacts with iodine dissolved in an organic solvent to give an iodide of formula SnIx, where x is a whole number. This experiment enables the formula to be found.
Weigh accurately about 3 g of iodine, and transfer it to a 250cm3 round-bottomed flask. Add to this 50cm3 of tetrachloroethylene solvent.
Weigh accurately about 5 g of tin metal, which should be in pieces no larger than 1cm square. Add the tin to the flask.
Clamp the flask by the neck over a gauze, and fit the flask with a vertical water condenser. This enables the mixture to be heated for a long time without loss of solvent; it is called heating under reflux.
Heat the mixture gently so that it just boils; continue heating until the liquid dropping from the condenser shows no trace of iodine coloration. Then allow the mixture to cool.
Decant the liquid from the residual tin into the large residues beaker in the fume cupboard, taking care not to lose any of the tin. Then wash the residual tin with two 20cm3 portions of propanone, which can be discarded down the main sink. Shake the tin on to a filter paper, and dry it, taking particular care not to lose any of the metal. Reweigh the dried tin.
Mass of iodine taken/g
Final mass of tin/g:
Initial mass of tin/g:
Mass of tin used in the reaction/g:
1. What was the colour of the mixture (a) at the start, (b) at the end?
2. How many moles of iodine atoms reacted with the tin? (Molar mass of iodine atoms = 127g)
3 How many moles of tin reacted with the iodine? (Molar mass of tin = 119g)
4 What is the value of x?
5 The tin iodide formed is soluble in organic solvents; what type of bonding do you think it has?
6 There are various errors possible with this experiment. Explain the effect of each of the following on the value of x obtained:
(i) Incomplete reaction of the iodine.
(ii) Poor washing of the tin so that it remains contaminated with the product.
(iii) Incomplete drying of the tin metal at the end of the reaction.
(iv) Loss of iodine vapour from the top of the reflux condenser.
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