- The 7 diatomic elements: H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂
- Swap-and-drop to write ionic formulae: swap the charge numbers and drop the sign
- Subscripts inside formulae must NEVER be changed to balance an equation — use coefficients only
- State symbols: (s), (l), (g), (aq)
- Mass is conserved in ALL chemical reactions
- In an open system, apparent mass loss = gas escaping; apparent mass gain = gas absorbed from air
- Common polyatomic ions: NH₄⁺, OH⁻, NO₃⁻, CO₃²⁻, SO₄²⁻, PO₄³⁻
- Brackets are used when more than one polyatomic ion is needed: Mg(OH)₂, Al₂(SO₄)₃
This key facts covers Key Facts to Know within Formulae, Equations and Conservation of Mass for GCSE Chemistry. Revise Formulae, Equations and Conservation of Mass in Quantitative Chemistry for GCSE Chemistry with 13 exam-style questions and 12 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 9 of 14 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Formulae, Equations and Conservation of Mass
Which of the following is the correct formula for oxygen gas?
Explain why mass is conserved in a chemical reaction.
Quick recall flashcards
Name the seven diatomic elements.
H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂
Mnemonic: Have No Fear Of Ice Cold Beer
State the law of conservation of mass.
In a chemical reaction, the total mass of the products equals the total mass of the reactants.
No atoms are created or destroyed — they are only rearranged.