lesson
A mole connects mass with particle amount
1 · Learn
Amount in moles equals mass divided by molar mass when compatible units are used. Molar mass in grams per mole connects a measured mass in grams to an amount. Balanced equation coefficients give mole ratios.
Do not use mass ratios directly as though they were molecule ratios. State the supplied relative masses rather than expecting an unstated periodic-table value.
2 · Worked example
With molar mass 18 g/mol, 36 g of water is 2 mol. A 2:1 coefficient ratio would compare amounts, not equal masses.
3 · Your turn
A substance has molar mass 44 g/mol. How many moles are in 22 g?
Check your answer
0.5 mol.
4 · Apply your learning
Check units and explain why equal mole amounts of different substances need not have equal masses.
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Check a calculation · Year 5 onward
Use this only when your teacher or adult allows a calculator for the task. Show your thinking first. It does not replace mental or written arithmetic and does not mark your lesson answer.
Powers, roots and trigonometry · Year 7 onward
Use only when the task allows a calculator. Choose one operation at a time and record your working. Trigonometry here always uses degrees (DEG), not radians. Inverse sine, cosine and tangent return an angle, not a reciprocal. Keep exact fractions and π in answers when requested.
Approximate numerical results use up to 12 significant digits. Inverse sine returns −90° to 90°, inverse cosine 0° to 180°, and inverse tangent −90° to 90°; these are principal values, not every possible solution of a trigonometric equation.
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