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Author Topic: Calculate the percentage purity....  (Read 8007 times)

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devvaibhav

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Calculate the percentage purity....
« on: June 11, 2011, 04:08:09 AM »

Q:- An impure sample of NaCl, which weighed 0.50 g, gave on treatment with excess of AgNO3 solution, 0.90 g of AgCl as precipitate. Calculate the percentage purity of the sample.

Reaction: NaCl + AgNO3  :rarrow: NaNO3 + AgCl

The formula for percentage purity is : (Pure/Total wt.) * 100
Is this correct?

My attempt to the solution: 143.5 g of AgCl will be given by = 58.5 g of pure NaCl
Therefore, 0.9 g of Agcl will be given by = (58.5/143.5)*0.9 = 0.36 g of pure NaCl

We have 0.36 g pure NaCl(by calculation) and total wt. = 0.50 g.

Therefore, percentage purity= (0.36/0.50)*100 = 72 %
But it is incorrect. The correct answer is 73.4 %
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Borek

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Re: Calculate the percentage purity....
« Reply #1 on: June 11, 2011, 04:43:51 AM »

Your approach is correct, but don't round down intermediate values.

Technically correct answer should be 73%, as it will have two significant figures, like data. But significant figures are not that important.
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