Chemistry study notes

Chemical Calculations

Write formulae and equations, then calculate moles, mass and molar mass.

SEC G2 Science K223 / K225 (2027)

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3 topics

Scope

4. Chemical Calculations (K223 / K225). Use the outcome map to find the explanation for a particular syllabus requirement.

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4.1(a) Use chemical symbols and formulae
- Element symbols
- Formulae of named syllabus compounds
Read and construct formulae
4.1(b) Translate atom counts and formulae
- Subscripts, brackets and coefficients
- Reverse interpretation
Read and construct formulae
4.1(c) Balance ion charges to obtain formulae
- Simple and polyatomic ions
- Deduce ion charge from formula
Read and construct formulae
4.1(d) Interpret equations and states
- s, l, g and aq
- Coefficients as mole ratios
Balance atoms, then account for ions
4.1(e) Construct balanced equations
- Full equations with states
- Ionic equations and spectators
- Conserve atoms and charge
Balance atoms, then account for ions
4.2(a) Define relative atomic mass
- Carbon-12 comparison
- Average atomic mass
The mole is a counting unit
4.2(b) Define and calculate relative molecular/formula mass
- Sum relative atomic masses
- Molecular versus ionic terminology
The mole is a counting unit
4.2(c) Calculate amount, mass and molar mass
- n = m / M, rearranged as needed
- Molar mass equals the relative mass in g/mol
- Reacting masses and gas volumes not required
The mole is a counting unit