Question

THE density of 3M aqueous solution of sodium thiosulphate is 1.25g/mL. Calculate 1. mole fraction of sodium thiosulphate

2. molalities of Na+ and S2O32-

Answer 1

Molecular weight of sodium thiosulphate penta-hydrate = 248 ; 

1000 ml of 3M solution contains 248 X 3 g thiosulphate ; 

1 ml of 3M solution contains (248 X 3)/1000 g or 0.744 g thiosulphate. 

Amount of water per ml of aqueous thiosulphate solution 

= 1.25 - 0.744 = 0.506 g . 

Mole fraction of thiosulphate = (mole of thiosulphate)/(total number of moles) 

= (0.744/248) / {(0.744/248) + (0.506/18)} 

= 0.003/(0.003 + 0.02811) 

= 0.0964 . 

Molarity of Sodium & thiosulphate ions: 

One molecule of thiosulphate produces 2 atoms of sodium ; 

One mole of thiosulphate produces 2 moles of sodium ; 

1000 ml of 3M thiosulphate will produce 2 X 3 gram-atoms or 6 gram-atoms of 

sodium and 3 moles of thiosulphate ions.

Answer 2

Answer:

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Explanation:

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