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WAEC (WASSCE) Chemistry · Matter, atoms and chemical combination

Stoichiometry and chemical reactions: WAEC Chemistry Past Questions and Answers

What the WAEC syllabus covers in Stoichiometry and chemical reactions

Our summary: Chemical symbols, formulae and equations, the laws of chemical combination, the mole, and calculations with solutions.

  • Symbols, formulae and equations (Symbols of the first thirty elements and other common elements that are not among the first thirty elements.)
  • Chemical symbols
  • Empirical and molecular formulae (Calculations involving formulae and equations will be required. Mass and volume relationships in chemical reactions and the stoichiometry of such reactions such as: calculation of percentage composition of element.)
  • Chemical equations and IUPAC names of chemical compounds ((1) Combustion reactions (including combustion of simple hydrocarbons). (2) Synthesis. (3) Displacement or replacement. (4) Decomposition. (5) Ionic reactions.)
  • Laws of chemical combination ((1) Laws of conservation of mass. (2) Law of constant composition. (3) Law of multiple proportions. Explanation of the laws to balance given equations. (4) Experimental illustration of the law of conservation of mass.)
  • Amount of substance ((1) Mass and volume measurements. (2) The mole as a unit of measurement; Avogadro's constant, L = 6.02 × 10²³ entities mol⁻¹. (3) Molar quantities and their uses. (4) Moles of electrons, atoms, molecules, formula units etc.)
  • Mole ratios (Use of mole ratios in determining stoichiometry of chemical reactions. Simple calculations to determine the number of entities, amount of substance, mass, concentration, volume and percentage yield of product.)
  • Solutions ((1) Concept of a solution as made up of solvent and solute. (2) Distinguishing between dilute solution and concentrated solution. (3) Basic, acidic and neutral solutions.)
  • Concentration terms (Mass (g) or moles (mol) per unit volume. Emphasis on current IUPAC chemical terminology, symbols and conventions. Concentration be expressed as mass concentration, g dm⁻³, molar concentration, mol dm⁻³.)
  • Standard solutions ((1) Preparation of some primary standards e.g. anhydrous Na₂CO₃, (COOH)₂·2H₂O/H₂C₂O₄·2H₂O. (2) Meaning of the terms primary standard, secondary standard and standard solution.)
  • Preparation of solutions from liquid solutes by the method of dilution (Dilution factor.)

Syllabus content © The West African Examinations Council (WASSCE (harmonised West African syllabus)).

WAEC (WASSCE) Chemistry questions on Stoichiometry and chemical reactions

  1. WAEC 2024Ethane of volume 400 cm ^3 was completely burnt in excess oxygen according to the following equation: 2C 2 H 6 (g) + 7O 2 (g) → 6H 2 O (g) + 4CO 2 (g) Calculate…
  2. WAEC 2024The volume of 22g of CO 2 at stp is equivalent to [C =12, O =16, molar volume at stp = 22.4 dm ^3 ]
  3. WAEC 2024The percentage by mass of Oxygen in MgSO 4 .7H 2 O is [ M r of MgSO 4 .7H 2 O = 246 ]
  4. WAEC 2024Consider the reaction represented by the equation: C 3 H 8 + 5 O 2 → 3CO 2 + 4H 2 O If 0.1 mole of C 3 H 8 was completely burnt, what volume of CO 2 would be…
  5. WAEC 2024Consider the reaction represented by the following equation: x Al + yCl 2 → z AlCl 3
  6. WAEC 2023How many grammes of NaOH(s) would be needed to produce 100.0 cm3 of a 0.20 mol dm^ -3 NaOH, (aq)? [NaOH = 40.0]
  7. WAEC 2023The relative molar mass of a gaseous hydrocarbon is 30. Determine its vapour density.
  8. WAEC 2023The vapour density of an organic compound with the molecular formula C 2H 4O 2 , is [H=1.0, C=12.0, O= 16.0]
  9. WAEC 2023Determine the volume of 0.100 mol of HCl in 0.250 mol dm^3 of solution.
  10. WAEC 2022If 60 g of M combines with 24 g of oxygen, what would the empirical formula of the oxide be? ( molar mass of M = 120, O = 16)
  11. WAEC 2022A hydrogen chloride gas reacted with oxygen gas to yield water and chlorine gas. The mole ratio of the hydrogen chloride gas to water is
  12. WAEC 2022If the molar mass of X(HCO3) 2 is 162 g mol ^ -1 , determine the relative atomic mass of X. [H = 1.0, C = 12.0, 0 = 16.0]
  13. WAEC 2022What is the percentage composition of carbon in Ca(HCO3) 2 ? [ Ca = 40.0, 0= 16.0, C = 12.0, H= 1.0]
  14. WAEC 2022Which of the following scientists formulated the law of conservation of mass?
  15. WAEC 2021What is the empirical formula of a hydrocarbon containing 0.160 moles of carbon and 0.640 moles of hydrogen
  16. WAEC 2021How many molecules of oxygen would occupy a volume of 2.24 cm ^ 3 at s.t.p? [Molar volume at s.t.p = 22,400 cm ^ 3 , Avogadro's number = 6.02 x 10 ^ 23 ]
  17. WAEC 2021The ratio of carbon atoms of hydrogen atoms in a hydrocarbon is 1:2. If its molecular mass is 56, what is its molecular formula?
  18. WAEC 2021Student X titrated 25 cm ^ 3 of Na 2 CO ^ 3 with 0.1 mol dm ^ -3 HCI, using methyl orange as indicator. Student Y carried out the same exercise but used…
  19. WAEC 2021What is the concentration of a solution which contains 0.28g of potassium hydroxide in 100 cm ^ 3 of solution [KOH = 56]
  20. WAEC 2020which of the following quantities is a molar quantity?
  21. WAEC 2020If 20 cm ^3 of sodium hydroxide was neutralized by 20 cm ^3 of 0.01 mol dm ^3 tetraoxosulphate(VI) acid, what is the concentration of the sodium hydroxide…
  22. WAEC 2020Dilution factor is the?
  23. WAEC 2020An alkanol containing 60% carbon by mass would have a molecular formula [H=1.0. C-12.0, O= 16.0]
  24. WAEC 2020What volume of oxygen at s.t.p is required to burn completely 7.5 dm ^3 of methane according to the following equation? CH 4 g + 20 2 g → CO 2 g + H 2 O g
  25. WAEC 2020How many moles of H 2 SO4 are there in 50 cm ^3 of 0.108 mol dm ^3 solution of the acid?
  26. WAEC 2020A balanced chemical equation is based on the law of?
  27. WAEC 2019What is the percentage by mass of H in CH 3 COOH ?
  28. WAEC 2019Which of the following pairs of components have the same molecular mass? [ H = 1.0, C = 12.0, O = 16.0 ]
  29. WAEC 2019An organic compound contains 72% carbon, 12% hydrogen and 16% oxygen by mass. What is the empirical formula of the compound? [ H = 1.0. C = 12.0, O = 16.0 ]
  30. WAEC 2019consider the following reaction equation: 2Al(OH) 3 + 3H 2 SO 4 →Al 2 (SO4) 3 (aq)+6H 2 O. How many moles of tetraoxosulphate(vi)acid is needed to produce…
  31. WAEC 2019Stoichiometry is based on the law?
  32. WAEC 2019If 6.5g of magnesium ribbon reacts completely with Hydrochloric acid, how many grams of hydrogen gas would be liberated? Mg(s) + 2 HCl(aq) -- MgCl 2(aq) + H…
  33. WAEC 2019The properties of a good primary standard solution include the following except?
  34. WAEC 2019Which of the following apparatus is NOT used in volumetric analysis?
  35. WAEC 2019How many moles of carbon(iv)oxide contains 16.0g of oxygen? [ C = 12.0, O = 16.0 ]
  36. WAEC 2018An organic compound has the empirical formula CH 2 . If its molar mass is 42 gmol^ -1 , what is its molecular formula? (C = 12.0, H = 1.0)
  37. WAEC 2018What is the relative molecular mass of a compound which has empirical formula CH 2 O ? [C= 12, H= 1, O= 16]
  38. WAEC 2018The empirical formula of a compound containing 0.067mol Cu and 0.066mol O is [Cu = 63.5, O = 16]
  39. WAEC 2018Analysis of a hydrocarbon shows that it contains 0.93g of Carbon per gram of the compound. The mole ratio of carbon to hydrogen in the compound is [H = 1.0…
  40. WAEC 2018The number of Hydrogen ions in 1.0 dm^ 3 of 0.02 moldm^ -3 tetraoxosulphate(VI) acid is [N A = 6.02 × 10^ 23 ]
  41. WAEC 2018How many atoms are contained in 0.2moles of nitrogen? [N A = 6.02 × 10^ 23 ]
  42. WAEC 2018What is the mass of solute in 500 cm^ 3 of 0.005 moldm^ -3 H 2 SO 4 ? ( H = 1, S = 32.0, O=16.0)
  43. WAEC 2018Consider the following reaction equation: 2HCl + Ca(OH) 2 CaCl 2 + H 2 O . What is the volume of 0.1 moldm^ -3 HCl that would completely neutralize 25 cm^ 3 of…
  44. WAEC 2018Which of the following CANNOT be an empirical formula?
  45. WAEC 2018The law of definite proportions states that
  46. WAEC 2017A 0.1 moldm^ -3 solution of sodium hydroxide was diluted with distilled water to 0.001 moldm^ -3 . What is the dilution factor?
  47. WAEC 2017The properties of a good primary standard include the following except
  48. WAEC 2017A hydrocarbon contained 14.3% hydrogen. The empirical formula for the hydrocarbon is [H= 1.0, C= 12.0]
  49. WAEC 2017The mass of one mole of (NH 4 ) 2 CO 3 is [O=16.0, N=14.0, C=12.0, H=1.0]
  50. WAEC 2016Consider the following reaction equation C2H4(g) + 3O2(g) 2CO2(g) + 2H2O(l). The volume of oxygen at s.t.p that will be required to burn 14g of ethene is [C2H4…

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