Number of moles of a substance =
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mass of substance in grams
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relative atomic or formula mass
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Concentration of solution, mol dm-3 =
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number of moles of solute
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volume of solution in dm3
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Relative atomic masses: H = 1, C = 12, O = 16, Na = 23, Mg = 24, Ca = 40, Br = 80, Ag = 108, Au = 197
1 The number of moles of atoms in 12g of carbon and 108g of silver are the same. Explain this statement.
2 A pure gold wedding ring weighs 4g. How many moles of gold atoms are there in the ring?
3 The ingredients label on a packet of salted crisps says that it contains 0.23g of sodium. How many moles of sodium ions does this represent?
4 What is the mass of 2 moles of calcium carbonate?
5 A 0.75 dm3 bottle of ginger beer contains 14.1g of sucrose, C12H22O11.
a What is the relative formula mass of the sucrose?
b How many moles of sucrose are in the ginger beer?
c What is the concentration of the sucrose in the ginger beer in mol dm–?
Extra challenge
6 A sample of magnesium bromide (MgBr2) weighs 46g. How many moles of magnesium ions and bromide ions are in the sample?
