Cambridge IGCSE · Chemistry 0620
IGCSE Chemistry: Stoichiometry — Practice Questions & Answers
Master moles, balanced equations, reacting masses, concentration, yield, purity, empirical formulae and gas volumes.
984 practice questions available for this topic — here are 10 with full answers and explanations.
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Practice questions with answers
1
Multiple choice · Easy
What is the correct chemical formula for calcium chloride?
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WhyCalcium forms a 2+ ion and chloride a 1- ion, so two chloride ions balance one calcium ion, giving CaCl2.
2
Multiple choice · Easy
Which number balances this equation? H2 + __ Cl2 -> 2HCl
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WhyTwo H atoms and two Cl atoms are on the right, so one H2 and one Cl2 are needed; the missing coefficient is 1.
3
Multiple choice · Easy
What is the relative molecular mass (Mr) of water, H2O? (Ar: H = 1, O = 16)
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WhyMr = (2 x 1) + 16 = 18.
4
Multiple choice · Easy
How many atoms in total are shown in one formula unit of CaCO3?
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WhyOne Ca, one C and three O atoms give a total of 5 atoms.
5
Fill in the blank · Easy
The amount of substance that contains 6.02 x 10^23 particles is called one .
Answer:
mole / mol
WhyOne mole is the amount of substance containing the Avogadro number (6.02 x 10^23) of particles.
6
Fill in the blank · Easy
In the equation 2H2 + O2 -> 2H2O, the number written in front of H2O to balance it is .
Answer:
2 / two
WhyTwo water molecules are needed to balance the four hydrogen and two oxygen atoms, so the coefficient is 2.
7
Multiple choice · Medium
How many moles are present in 88 g of carbon dioxide, CO2? (Mr of CO2 = 44)
- 2 mol
- 0.5 mol
- 4 mol
- 44 mol
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Whymoles = mass / Mr = 88 / 44 = 2 mol.
8
Multiple choice · Medium
What is the mass of 0.25 mol of sodium hydroxide, NaOH? (Mr = 40)
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Whymass = moles x Mr = 0.25 x 40 = 10 g.
9
Multiple choice · Medium
How many molecules are there in 0.5 mol of oxygen gas? (Avogadro constant = 6.02 x 10^23 /mol)
- 3.01 x 10^23
- 6.02 x 10^23
- 1.20 x 10^24
- 1.50 x 10^23
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Whynumber of molecules = moles x Avogadro constant = 0.5 x 6.02 x 10^23 = 3.01 x 10^23.
10
Multiple choice · Medium
What volume does 0.5 mol of a gas occupy at room temperature and pressure (r.t.p.)? (molar gas volume = 24 dm3/mol)
- 12 dm3
- 24 dm3
- 48 dm3
- 6 dm3
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Whyvolume = moles x 24 = 0.5 x 24 = 12 dm3.
Key terms in Stoichiometry
Stoichiometry: The study of the quantitative relationships between amounts of reactants and products in a chemical reaction.
Chemical formula: A symbolic representation showing the elements present in a substance and the ratio of their atoms.
Molecular formula: A formula that shows the actual number of atoms of each element present in one molecule of a compound.
Empirical formula: A formula that shows the simplest whole-number ratio of the atoms of each element in a compound.
Structural formula: A representation that shows how the atoms in a molecule are arranged and bonded together.
Displayed formula: A diagram showing all the atoms and all the bonds in a molecule drawn out individually.
Ionic formula: A formula showing the simplest ratio of cations to anions that produces an electrically neutral ionic compound.
Subscript: A small number written below and after a symbol indicating how many of that atom or group are present.
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