GCSE Combined Science Chemistry Core Formulas Cheat Sheet

Key Facts

• Relative formula mass is found by adding the relative atomic masses in a formula: $M_r = \sum A_r$.
• The number of moles is calculated using $n = \frac{m}{M_r}$, where $n$ is in mol, $m$ is in g, and $M_r$ is in g mol$^{-1}$.
• Mass can be found from moles using $m = nM_r$.
• Concentration in mol dm$^{-3}$ is calculated using $c = \frac{n}{V}$, where $V$ must be in dm$^3$.
• Mass concentration is calculated using $\text{concentration} = \frac{\text{mass of solute}}{\text{volume of solution}}$.
• At room temperature and pressure, gas volume can be estimated using $V = 24n$, where $V$ is in dm$^3$ and $n$ is in mol.
• Percentage yield is calculated using $\text{percentage yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100$.
• Atom economy is calculated using $\text{atom economy} = \frac{M_r\text{ of desired product}}{M_r\text{ of all products}} \times 100$.

Vocabulary

Relative atomic mass

Relative atomic mass, $A_r$, is the average mass of atoms of an element compared with $\frac{1}{12}$ of the mass of a carbon-12 atom.

Relative formula mass

Relative formula mass, $M_r$, is the total of the relative atomic masses of all atoms in a compound formula.

Mole

A mole is an amount of substance containing $6.02 \times 10^{23}$ particles.

Concentration

Concentration is the amount of solute dissolved in a given volume of solution, often measured in mol dm$^{-3}$ or g dm$^{-3}$.

Theoretical yield

The theoretical yield is the maximum mass of product predicted from a balanced chemical equation.

Atom economy

Atom economy is the percentage of reactant atoms that become part of the desired product.