Question

A 12.51 g sample of NaBr contains 22.34% Na by mass. Considering the law of constant...

A 12.51 g sample of NaBr contains 22.34% Na by mass. Considering the law of constant composition (definite proportions) how many grams of sodium does a 7.49 g sample of sodium bromide contain?

Homework Answers

Answer #1

It will contain 2.04 g of sodium.

We can work out the empirical formula of sodium bromide by writing down the ratio by which they combine in grams:

Na : Br

= 22.34 : 77.66

( I got 77.66 by subtracting 22.34 from 100 as it is a % age)

Now we get the ratio in moles by dividing each by the mass of I mole .

(Ar[Na]=23 Ar[Br]=80)

= 22.34/23 : 77.66/80

= 0.97 : 0.97

= 1 : 1

So the empirical formula is NaBr.

The Mr of sodium bromide is therefore 23 + 80 = 103.

This means that 103g of sodium bromide must contain 23g of sodium.

So 1g of sodium bromide must contain 23/103 g of sodium.

So 9.13 g of sodium bromide must contain 23/103 x 9.13 = 2.04 g of sodium.

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