Stoichiometry and the Mole Concept
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About this topic
This fundamental Form 3 topic introduces the mole concept, chemical equations, and stoichiometric calculations, which are central to quantitative chemistry in the Zambian curriculum. You will learn to define the mole in terms of Avogadro's constant, calculate relative atomic and formula masses, and determine empirical and molecular formulae. The ability to balance chemical equations and perform calculations involving reacting masses, volumes of gases, and concentrations of solutions is essential for solving complex problems in ECZ exams. This topic builds the mathematical foundation for chemistry, enabling you to analyze chemical processes quantitatively—a key competence for exam readiness and further studies in science.
What you'll practise (17 questions)
- The formula of copper (II) sulphate is CuSO₄. What is the percentage of sulphur in the compound? A) 100 B) 60 C) 40 D) 20
- 2.5g of impure copper (II) oxide reacted with 200cm³ of 0.125M sulphuric acid. What is the percentage purity of copper (II) oxide? A) 80% B) 60% C) 40% D) 20%
- If 0.1 mole of benzoic acid was reacted, calculate the volume of carbon dioxide expected to be produced at room temperature and pressure (r.t.p).
- If the volume of carbon dioxide obtained was 6.5 dm³, what was the percentage yield of the carbon dioxide?
- Calculate the concentration of 25.0cm³ of sulphuric acid that reacted with 25.0cm³ of aqueous potassium hydroxide whose concentration was 0.5M.
- Aluminium Sulphate can be obtained from the reaction: 2Al(OH)₃ + 3H₂SO₄ → Al₂(SO₄)₃ + 6H₂O. How many moles of sulphuric acid are needed to produce 0.5 mol of aluminium sulphate?
- What is the percentage yield when 6.4g of copper are heated in air and 7.6g of copper (II) oxide is obtained?
- Sodium reacts with water according to the equation: 2Na + 2H₂O → 2NaOH + H₂. Which volume of hydrogen is produced at r.t.p when 0.2 mol of sodium reacts?
- An element E forms a hydride EH₃, which contains 90% of E by mass. What is the relative atomic mass of E?
- When calcium carbonate is heated the following reaction takes place: CaCO₃(s) → CaO(s) + CO₂(g). Which volume of carbon dioxide at room temperature and pressure (r.t.p) would be produced if 150g of calcium carbonate is heated?
- Lead (II) nitrate reacts with potassium iodide according to the equation: Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s) + 2KNO₃(aq). The mass of lead (II) iodide that will be formed when 16.6g of potassium iodide reacts with excess lead (II) nitrate is...
- All ammonium salts on heating with sodium hydroxide produce ammonia gas. From which ammonium salt can the greatest mass of ammonia be obtained?
- 16g of Methane (CH₄) is burnt completely in oxygen to form carbon dioxide (CO₂) and water (H₂O). What mass of water would be produced?
- Calculate the mass of magnesium which was in excess when 0.03g of magnesium was added to 20cm³ of 0.10mol/dm³ hydrochloric acid.
- Calculate the volume of hydrogen that would be produced at r.t.p.
- What mass of carbon dioxide was lost when the reaction went to completion, if the initial mass of the beaker and its contents was 50.0g?
- Calculate the mass of calcium carbonate used in the first 1 minute.
Answer each question above to see the correct answer and a full explanation.