Practice neco model questions vol1 chemistry 2022 Past Questions

Question 1 View Details

Given a compound with molecular formula \(C_7H_8O_2\) that contains a carboxylic acid group attached directly to a benzene ring and a \(\mathrm{CH_2CH_2OCH_3}\) substituent positioned para to the carboxyl group, write the IUPAC name of the compound.

A. 4-(2-ethoxyethyl)benzoic acid

B. 3-(2-methoxyethyl)benzoic acid

Correct C. 4-(2-methoxyethyl)benzoic acid

D. 4-(2-methoxyethyl)phenylacetic acid

Correct Answer: C

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Question 2 View Details

A 0.10 M solution of a weak monoprotic acid HA ( \(K_a = 1.2 \times 10^{-5}\) ) has a volume of 50.0 mL. It is titrated with 0.10 M NaOH. After adding 75.0 mL of the base, calculate the pH of the solution.

A. 11.30

Correct B. 12.30

C. 9.75

D. 10.85

Correct Answer: B

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Question 3 View Details

The standard enthalpy of formation of carbon dioxide is \(\Delta_f H^\circ(\mathrm{CO_2(g)}) = -393.5\ \text{kJ mol}^{-1}\) and that of carbon monoxide is \(\Delta_f H^\circ(\mathrm{CO(g)}) = -110.5\ \text{kJ mol}^{-1}\). The O=O bond dissociation energy is 498 kJ mol\(^{-1}\). Using Hess's law, determine the average bond energy of a C=O bond in \(\mathrm{CO_2}\).

A. 470 kJ mol^{-1}

B. 420 kJ mol^{-1}

C. 398 kJ mol^{-1}

Correct D. 446 kJ mol^{-1}

Correct Answer: D

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Question 4 View Details

Balance the redox reaction between permanganate ion and ferrous ion in acidic medium, then determine the volume (in mL) of 0.200 M \(\mathrm{KMnO_4}\) solution required to completely oxidise 25.0 mL of 0.150 M \(\mathrm{FeSO_4}\) solution.

Correct A. 3.75 mL

B. 3.25 mL

C. 4.20 mL

D. 2.85 mL

Correct Answer: A

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Question 5 View Details

A 12.0 g sample of a mixture of 1‑butanol (\(\mathrm{C_4H_{10}O}\)) and 2‑butanol (\(\mathrm{C_4H_{10}O}\)) is oxidised with excess potassium dichromate in acidic medium. The oxidation converts 1‑butanol to butanoic acid (\(\mathrm{C_4H_8O_2}\)) and 2‑butanol to butan‑2‑one (\(\mathrm{C_4H_8O}\)). After the reaction, the combined mass of the two products obtained is 13.2 g. Assuming quantitative conversion, calculate the mass of 1‑butanol and the mass of 2‑butanol originally present in the mixture.

A. 1‑butanol: 6.5 g; 2‑butanol: 5.5 g

B. 1‑butanol: 7.5 g; 2‑butanol: 4.5 g

Correct C. 1‑butanol: 7.1 g; 2‑butanol: 4.9 g

D. 1‑butanol: 8.0 g; 2‑butanol: 4.0 g

Correct Answer: C

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Question 6 View Details

A 2.00 g mixture of ethene (\(C_2H_4\)) and propane (\(C_3H_8\)) is burnt completely in excess oxygen. The combustion produces \(6.10\) g of carbon dioxide and \(3.03\) g of water. Determine the mass of propane present in the original mixture (in grams).

A. 1.75

B. 0.85

Correct C. 1.30

D. 2.10

Correct Answer: C

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Question 7 View Details

Which element is located in period 4 and group 7 of the periodic table?

A. Iron (Fe)

Correct B. Copper (Cu)

C. Nickel (Ni)

D. Zinc (Zn)

Correct Answer: B

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Question 8 View Details

What is the maximum number of electrons that can occupy the third electron shell (\(n = 3\)) of an atom?

A. 8

B. 24

Correct C. 18

D. 12

Correct Answer: C

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Question 9 View Details

A sample of \(5.00\) g calcium carbonate (\(CaCO_3\)) is reacted with excess hydrochloric acid. The reaction is: \(CaCO_3 + 2HCl \rightarrow CaCl_2 + CO_2 + H_2O\). Only \(80\%\) of the theoretical amount of calcium chloride (\(CaCl_2\)) is obtained. The obtained \(CaCl_2\) is then reacted with excess sodium sulfate (\(Na_2SO_4\)) according to: \(CaCl_2 + Na_2SO_4 \rightarrow CaSO_4\downarrow + 2NaCl\). Calculate the mass of calcium sulfate (\(CaSO_4\)) produced (in grams).

A. 4.32

Correct B. 5.44

C. 5.00

D. 6.88

Correct Answer: B

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Question 10 View Details

A sample of a non‑metal oxide containing only phosphorus, hydrogen and oxygen is heated. The products are \(0.180\) g of water and \(0.500\) g of diphosphorus pentoxide (\(P_2O_5\)). Determine the empirical formula of the oxide.

A. H3PO3

Correct B. H3PO4

C. H4PO5

D. H2PO4

Correct Answer: B

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Question 11 View Details

A lake has a volume of \(2.0 \times 10^{6}\) L and an initial pH of 7.5. Acid rain adds a total of \(5.0 \times 10^{4}\) mol of \(\mathrm{H^{+}}\) uniformly to the lake water. To restore the lake to its original pH, limestone (\(\mathrm{CaCO_{3}}\)) is added, which reacts according to \(\mathrm{CaCO_{3} + 2H^{+} \rightarrow Ca^{2+} + CO_{2} + H_{2}O}\). Calculate the mass of limestone required (in kilograms) to bring the pH back to 7.5.

A. 5.0 \\times 10^{3} kg

B. 3.8 \\times 10^{3} kg

C. 1.2 \\times 10^{3} kg

Correct D. 2.5 \times 10^{3} kg

Correct Answer: D

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Question 12 View Details

An impure sample of ferrous sulfate heptahydrate (\(\mathrm{FeSO_{4}\cdot7H_{2}O}\)) weighing \(5.00\) g is dissolved in water and diluted to a final volume of \(250.0\) mL. A \(25.00\) mL aliquot of this solution is titrated with \(0.0200\) M potassium permanganate (\(\mathrm{KMnO_{4}}\)) in acidic medium. The reaction is \(\mathrm{MnO_{4}^{-} + 5Fe^{2+} + 8H^{+} \rightarrow Mn^{2+} + 5Fe^{3+} + 4H_{2}O}\). The volume of \(\mathrm{KMnO_{4}}\) required is \(12.5\) mL. Determine the percent purity of the original sample, assuming only \(\mathrm{FeSO_{4}\cdot7H_{2}O}\) contributes ferrous ions.

Correct A. 69.5 %

B. 55.2 %

C. 82.1 %

D. 73.8 %

Correct Answer: A

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Question 13 View Details

A galvanic cell is constructed as \(\mathrm{Zn(s) | Zn^{2+}(0.010\;M) || Cu^{2+}(0.10\;M) | Cu(s)}\) at \(25^{\circ}\mathrm{C}\). Standard reduction potentials are \(E^{\circ}_{\mathrm{Zn^{2+}/Zn}} = -0.76\) V and \(E^{\circ}_{\mathrm{Cu^{2+}/Cu}} = +0.34\) V. (a) Calculate the cell potential under the given conditions using the Nernst equation. (b) If the same cell is used to electrolyze water, what minimum external voltage must be applied, given that the thermodynamic voltage for water electrolysis is \(1.23\) V and the oxygen‑evolution overpotential is \(0.50\) V?

A. 1.02 V; 1.78 V

B. 1.20 V; 1.65 V

Correct C. 1.13 V; 1.73 V

D. 0.94 V; 1.68 V

Correct Answer: C

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Question 14 View Details

Equal volumes of \(0.010\) M \(\mathrm{Pb(NO_{3})_{2}}\) solution and \(0.020\) M potassium iodide (\(\mathrm{KI}\)) solution are mixed at \(25^{\circ}\mathrm{C}\). Lead(II) iodide (\(\mathrm{PbI_{2}}\)) precipitates according to \(\mathrm{Pb^{2+} + 2I^{-} \rightarrow PbI_{2}(s)}\). The solubility product of \(\mathrm{PbI_{2}}\) is \(K_{sp}=8.5 \times 10^{-9}\). (a) Calculate the mass of \(\mathrm{PbI_{2}}\) that precipitates per litre of the resulting mixture. (b) Determine the concentration of iodide ions remaining in solution after precipitation.

A. 2.10 g; 1.8 \times 10^{-3} M

B. 2.75 g; 2.0 \times 10^{-3} M

Correct C. 2.31 g; 2.6 \times 10^{-3} M

D. 1.85 g; 3.2 \times 10^{-3} M

Correct Answer: C

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Question 15 View Details

The vapor pressure of water can be estimated by the Antoine equation \(\log_{10} P = A - \frac{B}{C+T}\), where \(P\) is the pressure in mm Hg and \(T\) is the temperature in °C. For water in the range \(1^{\circ}\mathrm{C}\) to \(100^{\circ}\mathrm{C}\), the constants are \(A = 8.07131\), \(B = 1730.63\), and \(C = 233.426\). At a mountain station the atmospheric pressure is \(630\) mm Hg. Calculate the boiling point of water at this pressure (in °C).

A. 100.0 \(^\circ\)C

B. 85.6 \(^\circ\)C

Correct C. 94.8 \(^\circ\)C

D. 90.2 \(^\circ\)C

Correct Answer: C

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Question 16 View Details

Calcium carbonate reacts with hydrochloric acid according to \(\mathrm{CaCO_3(s) + 2 HCl(aq) \rightarrow CaCl_2(aq) + CO_2(g) + H_2O(l)}\). If 12.0 g of \(\mathrm{CaCO_3}\) are mixed with 25.0 mL of 0.500 M \(\mathrm{HCl}\), calculate (i) the theoretical mass of \(\mathrm{CaCl_2}\) formed, (ii) the volume of \(\mathrm{CO_2}\) gas produced at STP, and (iii) the percent yield of \(\mathrm{CaCl_2}\) when the actual mass obtained after purification is 0.55 g.

A. 0.694 g; 0.150 L; 85.0 %

B. 1.33 g; 0.280 L; 41.3 %

Correct C. 0.694 g; 0.140 L; 79.3 %

D. 0.600 g; 0.140 L; 73.5 %

Correct Answer: C

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Question 17 View Details

A buffer is prepared by mixing 50.0 mL of 0.200 M acetic acid \(\mathrm{CH_3COOH}\) with 30.0 mL of 0.150 M sodium acetate \(\mathrm{CH_3COONa}\). Then 5.00 mL of 0.100 M \(\mathrm{HCl}\) is added. Given \(K_a\) of acetic acid = \(1.8\times10^{-5}\), calculate the pH of the resulting solution.

A. 5.02

Correct B. 4.33

C. 4.55

D. 4.10

Correct Answer: B

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Question 18 View Details

The solubility product of silver chloride is \(K_{sp}=1.8\times10^{-10}\).\n(a) Calculate the molar solubility of \(\mathrm{AgCl}\) in pure water.\n(b) Determine its solubility when 0.010 M \(\mathrm{NaCl}\) is present (common‑ion effect).\n(c) If 0.010 M ammonia is added, forming the complex \(\mathrm{[Ag(NH_3)_2]^+}\) with overall formation constant \(\beta_2=1.6\times10^{7}\), calculate the new molar solubility of \(\mathrm{AgCl}\). Assume the ammonia concentration remains essentially 0.010 M.

A. 1.0×10⁻⁴ M; 2.5×10⁻⁸ M; 3.0×10⁻³ M

B. 9.5×10⁻⁶ M; 9.0×10⁻⁹ M; 2.5×10⁻³ M

C. 2.12×10⁻⁵ M; 3.6×10⁻⁸ M; 8.5×10⁻⁴ M

Correct D. 1.34×10⁻⁵ M; 1.8×10⁻⁸ M; 1.70×10⁻³ M

Correct Answer: D

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Question 19 View Details

A 2.00 g sample of an unknown compound containing only carbon, hydrogen and oxygen is completely combusted, producing 4.00 g of \(\mathrm{CO_2}\) and 1.64 g of \(\mathrm{H_2O}\). (a) Determine the empirical formula of the compound. (b) If its molar mass is approximately 176 g·mol⁻¹, find its molecular formula.

A. Empirical formula C₃H₆O; Molecular formula C₉H₁₈O₃

B. Empirical formula C₄H₈O₂; Molecular formula C₁₆H₃₂O₈

C. Empirical formula C₂H₆O; Molecular formula C₁₀H₂₄O₅

Correct D. Empirical formula C₂H₄O; Molecular formula C₈H₁₆O₄

Correct Answer: D

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Question 20 View Details

A 10.0 g sample of an unknown hydrocarbon‑oxygen compound is burned completely in excess oxygen, producing 5.6 L of \(\mathrm{CO_2}\) and 4.5 L of \(\mathrm{H_2O}\) vapour at STP (22.4 L mol⁻¹). Determine the mass percent of carbon in the original sample.

A. 25.0 %

B. 40.0 %

Correct C. 30.0 %

D. 35.0 %

Correct Answer: C

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Question 21 View Details

The diagram shows a Bohr model of an atom with three electron shells. The innermost shell contains 2 electrons, the second shell contains 8 electrons and the outermost shell contains 1 electron. How many electrons are present in the outermost shell?

Correct A. 1

B. 2

C. 0

D. 3

Correct Answer: A

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Question 22 View Details

Standard reduction potentials at 25 °C are: \(\mathrm{Cu^{2+}+2e^- \rightarrow Cu(s)}\) \(E^{\circ}=+0.34\ \text{V}\) and \(\mathrm{Zn^{2+}+2e^- \rightarrow Zn(s)}\) \(E^{\circ}=-0.76\ \text{V}\). A galvanic cell is set up with a Zn(s) electrode immersed in 1.0 M ZnSO\(_4\) and a Cu(s) electrode immersed in 0.10 M CuSO\(_4\).\n(a) Write the overall cell reaction.\n(b) Calculate the cell EMF at 25 °C.\n(c) Determine the equilibrium constant \(K\) for the cell reaction.

A. E = 0.85 V; K ≈ 5.0×10^30

B. E = 1.12 V; K ≈ 3.0×10^38

C. E = 0.98 V; K ≈ 2.0×10^34

Correct D. E = 1.07 V; K ≈ 1.5×10^37

Correct Answer: D

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Question 23 View Details

The diagram shows the Lewis structure of methane (CH\(_4\)). What is the hybridisation of the central carbon atom?

A. sp

B. sp²

C. sp³d

Correct D. sp³

Correct Answer: D

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Question 24 View Details

1‑Phenylpropene (\(\mathrm{C_6H_5CH=CHCH_3}\)) is treated with excess HBr in the presence of peroxides, and the resulting alkyl bromide is subsequently hydrolysed with aqueous NaOH. Write the structural formula of the final product and give its IUPAC name.

A. Structural formula: C₆H₅CH₂CH(Br)CH₃; IUPAC name: 2‑bromo‑1‑phenylpropane (1‑phenyl‑2‑bromopropane)

B. Structural formula: C₆H₅CH₂CH(OH)CH₂Cl; IUPAC name: 2‑hydroxy‑1‑phenyl‑2‑chloropropane (1‑phenyl‑2‑chloropropan‑2‑ol)

C. Structural formula: C₆H₅CH₂CH₂CH₂OH; IUPAC name: 3‑hydroxy‑1‑phenylpropane (1‑phenyl‑3‑propanol)

Correct D. Structural formula: C₆H₅CH₂CH(OH)CH₃; IUPAC name: 2‑hydroxy‑1‑phenylpropane (1‑phenyl‑2‑propanol)

Correct Answer: D

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Question 25 View Details

A compound contains 40.0 % C, 6.7 % H and 53.3 % O by mass. Its molar mass is 180 g·mol\(^{-1}\). Determine its empirical formula and its molecular formula.

A. Empirical formula: CHO; Molecular formula: C₆H₆O₆

B. Empirical formula: C₂H₄O; Molecular formula: C₁₂H₂₄O₁₂

C. Empirical formula: C₃H₆O₃; Molecular formula: C₉H₁₈O₉

Correct D. Empirical formula: CH₂O; Molecular formula: C₆H₁₂O₆

Correct Answer: D

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