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QLDChemistryQuick questions
Unit 1: Chemical fundamentals (structure, properties and reactions)
Quick questions on The mole concept and stoichiometric calculations (QCE Chemistry Unit 1)
14short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is core conversions?Show answer
QCAA-relevant constants and conventions for 2026:
What is working with balanced equations?Show answer
A balanced chemical equation gives mole ratios between reactants and products. The coefficients are read as "moles per mole".
What is limiting reagent and theoretical yield?Show answer
When two or more reactants are mixed in non-stoichiometric amounts, one will run out first. That is the limiting reagent; it caps the maximum (theoretical) yield. The other is the excess reagent.
What is percentage yield?Show answer
The theoretical yield is the maximum predicted from stoichiometry assuming the limiting reagent reacts completely. Actual yield is what you measured in the lab.
What is gas volume calculations?Show answer
At STP (25 degrees C, 100 kPa per QCAA convention), 1 mole of any ideal gas occupies 24.79 L.
What is solution stoichiometry?Show answer
For aqueous reactions, the link between volume and moles is through concentration:
What is empirical and molecular formulae?Show answer
QCE Chemistry expects you to determine empirical formulae from percentage composition or combustion data, then scale to a molecular formula using the molar mass.
What is significant figures and units?Show answer
QCAA penalises unit errors and over-precise answers. Default to matching the least precise input (usually 3 significant figures). Express:
What is forgetting to balance the equation?Show answer
Stoichiometric ratios come from the coefficients. An unbalanced equation gives wrong ratios.
What is comparing mass directly instead of moles?Show answer
"Which is in excess, 10 g of A or 10 g of B?" cannot be answered from mass alone; convert to moles first.
What is using mL in n = cV?Show answer
V must be in litres. Convert mL by dividing by 1000.
What is choosing the limiting reagent from raw moles?Show answer
Divide each moles by its stoichiometric coefficient before comparing. The smallest quotient identifies the limiting reagent.
What is mixing STP conventions?Show answer
QCAA Year 12 uses 25 degrees C, 100 kPa giving 24.79 L/mol. Some older sources use 22.41 L/mol at 0 degrees C, 101.325 kPa. Check the formula sheet.
What is reporting yield above 100 percent without comment?Show answer
This usually signals impurity or weighing error. Recognise and flag.