Question

How many molecules of iron sulphate are in 250ml of the solution?
How many ions fe3+ does the 50ml solution contain?

Answer 1

Solution.

1.

$\frac{m}{M} = \frac{N}{Na}$

$C = \frac{m}{M \times V} = \frac{N}{Na \times V}$

$N = C \times Na \times V$

$N = 1 \ M \times 6.02 \times 10^{23} \times 0.25 = 1.51 \times 10^{23}$

2.

$Fe2(SO4)3 = 2Fe^{3+} + 3SO4^{2-}$

$C(Fe^{3+}) = C(Fe2(SO4)3) \times 2$

$C(Fe^{3+}) = 1 \ M \times 2 = 2 \ M$

Answer:

1.

$N = 1.51 \times 10^{23}$

2.

$C(Fe^{3+}) = 2 \ M$