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A balanced equation gives particle and mole ratios, not a direct mass ratio. Convert mass to moles first, use the stoichiometric ratio, then convert to the quantity requested.
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Match practice to your actual course
Curriculum levels describe progress rather than fixed attainment deadlines. Qualifications Scotland replaced SQA in February 2026; older resources may still carry the SQA name. We confirm the course and tutor match before arranging lessons. Early learning · P1–P7 · S1–S6. Your school’s subject choices, topic sequence and assessment tasks determine the detailed plan. The practice set below samples moles, reactions and solutions; it is not a complete syllabus or an official exam paper.
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Prepare a useful question for your tutor
Bring one attempted question and show your working or first draft. Explain what you tried and where the reasoning stopped. Together, identify whether the difficulty is changing subscripts to balance an equation or a missing prerequisite, then try a fresh problem independently.
Understand it. Try it. Review it.
Put your chemistry learning into practice.
Worked example · Moles, reactions and solutions
Find the amount in 9 g of water. Use molar mass 18 g/mol.
Use n = m/M.
n = 9/18 = 0.5.
There are 0.5 mol of water.
Common mistakes to check
Changing subscripts to balance an equation
Using millilitres in a concentration formula that requires litres
Preview the worksheet 