Calculating masses from equations and given masses - (higher tier)

Balanced equations and relative formula mass can be used to calculate the mass of product made from a given mass of reactant, and vice versa.

Example:

What mass of nitrogen is needed to make 120 g of nitrogen monoxide? (Mr of NO = 30) (Mr of N2 = 28)

N2(g) + O2(g) → 2NO(g)

moles = \frac{mass~(g)}{M_r}

moles = \frac{120}{30}

= 4 mol

1 mol N2 : 2 mol NO.

2 mol of N2 makes 4 mol of NO.

Mass of 2 mol of N2 = moles x Mr

= 2 × 28

= 56 g