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Quantitative chemistry - (CCEA) Calculate masses from equations (Higher)

Chemists use relative atomic masses and relative formula masses to carry out mole calculations.

Part of Chemistry (Single Science)Structures, trends, chemical reactions, quantitative chemistry and analysis

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

and 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? (M_r of NO = 30) (M_r 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 M_r

= 2 × 28

= 56 g

Limiting reactants - (higher tier)

Industrial quantities - (higher tier)

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