Question

How many molecules are in 0.25 grams of dinitrogen pentoxide?

Answer 1

Answer: $0.014\times 10^{23}molecules$

Explanation: Moles can be calculated by using the formula:

$\text{no of moles}=\frac{\text{given mass}}{\text{Molecular mass}}$

$\text{no of moles}=\frac{0.25g}{108g/mol}=0.002moles$

1 mole of $N_2O_5$ contains =$6.023\times 10^{23}molecules$

0.002 mole of $N_2O_5$ contains =$\frac{6.023\times 10^{23}}{1}\times 0.002=0.014\times 10^{23}molecules$

Answer 2

In order to get the answer, you have to know the formula of how to convert grams to mole and by that you can get the number of molecules.
The answer is 2 moles of N2O5. This is shown by the solution:
(0.25 g N2O5) (1 mol/ 108 g)=2.31 molecules
The answer is 2 molecules.