# What is the mass in grams of 4.03 x 10(23) H2 molecules at STP?

Dec 5, 2014

The asnwer is $1.34 g r a m s$.

One mole of diatomic hydrogen, ${H}_{2}$, has $6.022 \cdot {10}^{23}$ ${H}_{2}$ molecules, and weighs approximately $2 g r a m s$.

However, just by looking at the number of ${H}_{2}$ molecules given, you can estimate that this amounts to less than $1$ mole.

$4.03 \cdot {10}^{23}$ molecules * ($1$ mole)/($6.022 \cdot {10}^{23}$molecules) = $0.67$ moles of ${H}_{2}$.

Therefore, the mass is equal to

$0.67$ moles * $2 \frac{g}{m o l} = 1.34 g r a m s$ of ${H}_{2}$.