NECO Chemistry Practical Questions and Answers 2026
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*NECO 2026 CHEMISTRY PRACTICAL (PAPER 1 – ALT TO PRACTICAL)* *COMPLETE ANSWERS – QUESTIONS 1, 2 & 3* =========================================================== QUESTION 1: TITRATION (A vs B) =========================================================== A = Dibasic acid H₂X (in burette) B = NaOH solution (1.00 g in 250 cm³) Pipette volume = 25.00 cm³ (assumed – use your actual) Indicator = Methyl orange (a)(i) Sample titration results Volume of pipette used = 25.00 cm³ Titration Rough 1 2 3 Final burette reading (cm³) 24.80 24.60 24.70 24.70 Initial burette reading (cm³) 0.00 0.00 0.00 0.00 Volume of A used (cm³) 24.80 24.60 24.70 24.70 Average volume of A used = (24.60 + 24.70 + 24.70) ÷ 3 = 74.00 ÷ 3 = 24.67 cm³ Answer: 24.67 cm³ (a)(ii) Write a balanced equation for the reaction H₂X(aq) + 2NaOH(aq) → Na₂X(aq) + 2H₂O(l) (b)(i) Concentration of B in mol/dm³ (6 marks) Molar mass of NaOH = Na(23) + O(16) + H(1) = 40 g/mol Mass of NaOH = 1.00 g in 250 cm³ Concentration in g/dm³ = (1.00 ÷ 250) × 1000 = 4.00 g/dm³ Concentration in mol/dm³ = 4.00 ÷ 40 = 0.100 mol/dm³ Answer: 0.100 mol/dm³ (b)(ii) Concentration of A in mol/dm³ (4 marks) From equation: 1 mol H₂X : 2 mol NaOH Ca × Va / na = Cb × Vb / nb Ca = (Cb × Vb × na) / (Va × nb) = (0.100 × 25.00 × 1) / (24.67 × 2) = 2.50 / 49.34 = 0.0507 mol/dm³ Answer: 0.0507 mol/dm³ (b)(iii) Molar mass of A (2 marks) Given: Solution A contains 4.85 g/dm³ of the acid Molar mass = mass concentration ÷ molar concentration = 4.85 ÷ 0.0507 = 95.66 g/mol Answer: 95.7 g/mol (c) Why a standard solution of NaOH cannot be made by weighing and dissolving (2 marks) Sodium hydroxide is hygroscopic – it absorbs moisture from the air. It also reacts with carbon dioxide in the atmosphere to form sodium carbonate. This makes it impossible to weigh out a pure, exact mass of NaOH. Therefore, a standard solution of NaOH must be prepared and then standardised against a primary standard. =========================================================== QUESTION 2: QUALITATIVE ANALYSIS (Specimen C) =========================================================== Specimen C = Copper(II) tetraoxosulphate(VI) salt (CuSO₄·5H₂O) (a) C + 5 cm³ distilled water, shake thoroughly Test Observation Inference C + distilled water Blue solution forms. The salt dissolves completely in water. C is a soluble copper(II) salt. Blue colour indicates Cu²⁺ ions present. (b)(i) First portion + NaOH in drops, then excess Test Observation Inference NaOH drops Blue precipitate forms. Cu²⁺ ion present. NaOH excess Blue precipitate does NOT dissolve. Cu(OH)₂ is insoluble in excess NaOH. Confirms Cu²⁺. Equation: Cu²⁺(aq) + 2OH⁻(aq) → Cu(OH)₂(s) (blue) (b)(ii) Second portion + dilute NH₃ in drops, then excess Test Observation Inference NH₃ drops Blue precipitate forms. Cu²⁺ ion present. NH₃ excess Blue precipitate dissolves to form a deep blue solution. Formation of [Cu(NH₃)₄]²⁺ complex ion confirms Cu²⁺. Equation: Cu²⁺(aq) + 4NH₃(aq) → [Cu(NH₃)₄]²⁺(aq) (deep blue) (b)(iii) Third portion + BaCl₂ solution Test Observation Inference BaCl₂ added White precipitate forms. SO₄²⁻ ion present. (b)(iv) Add dilute HCl in excess to the mixture Test Observation Inference HCl added White precipitate does NOT dissolve. Barium sulphate (BaSO₄) is insoluble in dilute HCl. Confirms SO₄²⁻. Equation: Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s) (white) Overall conclusion: Specimen C contains Cu²⁺ ions and SO₄²⁻ ions. It is copper(II) tetraoxosulphate(VI) (CuSO₄). =========================================================== QUESTION 3: THEORY QUESTIONS =========================================================== (a) Titration of tetraoxosulphate(VI) acid with sodium trioxocarbonate(IV) (i) Name a suitable indicator (1 mark) Methyl orange (ii) Colour of indicator (1 mark) I. In the base (sodium trioxocarbonate(IV) solution) – yellow II. At the endpoint – orange (or pink) (iii) Why was the indicator used? (1 mark) The indicator is used to show the endpoint of the titration by changing colour when the reaction is complete, indicating that all the acid has been neutralised. (iv) State two precautions to ensure accurate burette readings (2 marks) 1. Read the burette at eye level to avoid parallax error. 2. Ensure the burette is free from air bubbles before taking readings. (v) Name the type of reaction that takes place (1 mark) Neutralisation reaction (or acid-base reaction). (b)(i) Apparatus used in the laboratory (2 marks) I. To determine the volumetric composition of water – Eudiometer (or Hofmann's voltameter) II. To produce an intermittent supply of a gas – Kipp's apparatus (b)(ii) Why is silver trioxonitrate(V) solution (AgNO₃) stored in amber-coloured reagent bottle? (1 mark) Silver trioxonitrate(V) is light-sensitive. It decomposes in the presence of light to silver metal, nitrogen dioxide, and oxygen. The amber-coloured bottle protects it from light. =========================================================== END OF ANSWERS =========================================================== INSTRUCTIONS FOR THE EXAM Answer ALL questions. Record all burette readings to 2 decimal places. Ensure concordant titres (within 0.10 cm³). Record all observations and inferences accurately. Time: As specified in your paper.
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