NSMQ 2023 CHEMISTRY PAST QUESTIONS AND ANSWERS.

What is the most likely mode of decay for each of the following nuclides?

1. Carbon – 15

Ans: Beta decay

2. Uranium – 238 (atomic number 92)

Ans: alpha decay

3. Nitrogen – 12

Ans: positron emission (or electron capture)

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1. 100.0 g of an inorganic compound is found to contain 34.0 g of copper, 15.0 g of nitrogen, and 51.2 g of oxygen. Determine the empirical formula of the compound given that the atomic mass (g/mol) of Cu, N, and O is 64.0, 14.0, and 16.0, respectively.

Ans: CuN₂O₆          [OR Cu (NO₃)₂]

Cu = 34.0/64 =0.53          N = 15.0/14 = 1.1             O = 51.2/16 = 3.2             Hence ratio = 1: 2: 6

2. 30.1 g of an inorganic compound is found to contain 15.0 g of copper, 7.62 g of sulphur, and 7.58 g of oxygen. Determine the empirical formula of the compound given that atomic masses (g/mol) of Cu, N, and O are 64.0, 14.0, and 16.0, respectively.

Ans: CuSO₂

Cu = 15.0/64 = 0.234           S = 7.50/32 = 0.234       O = 7.58/16 = 0.474   Hence ratio = 1: 1: 2

3. 40.0 g of an inorganic compound is found to contain 20.4 g of copper, 3.88 g of carbon, and 15.6 g of oxygen. Determine the empirical formula of the compound given that atomic masses (g/mol) of Cu, C, and O are 64.0, 12.0, and 16.0, respectively.

Ans: CuCO₃

Cu = 20.4/64 =0.32               C = 3.88/12 = 0.32       O = 15.6/16 = 0.98       Hence ratio = 1: 1: 3

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1. The gaseous molecules, methane and oxygen, are mixed in a 2:1 ratio by mass. What is the ratio of gases by volume? Take atomic masses (g/mol) of C, H, and O as 12, 1.0, and 16, respectively.

Ans: 1:1

Molecular mass of CH₄ = 16

Molecular mass of O₂ = 32

Hence, if present in a 2:1 ratio, the number of moles and volume will be the same, hence 1:1

2. Determine the sum of the stoichiometric coefficients of all reactants and products in a balanced equation of the reaction: N₂ + O₂ + H₂O → HNO₃

Ans: 13

2N₂ + 5O₂ + 2H₂O → 4HNO₃

3. The elements X and Y have 6 and 3 electrons, respectively, in their outermost shell. What is likely to be the formula of the compound formed between X and Y?

Ans: Y₂X₃

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1. Determine the most ionic compound in the list below:

CaCl₂; KCl; MgCl₂; AlCl₃; CsCl

Ans: CsCl

2. Which of the following compounds will exhibit the most hardness?

MgO; Al₂O₃; Na₂O; CaO; Li₂O

Ans: Al₂O₃

3. Which of the following compounds has the highest covalent character?

LiCl; NaCl; BeCl₂; RbCl; MgCl₂

Ans: BeCl₂               

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1. 0.25 mol of a hydrocarbon with an empirical formula C₃H₅ has a mass of 41 g. Determine the molecular formula of the compound. Take the atomic mass of carbon and hydrogen (g/mol) as 12 and 1.0, respectively.

Ans: C₁₂H₂₀

Molar mass = 41/0.25 = 164 g/mol

n = 164/41 = 4; Hence molecular formular = C12H20

2. An organic compound has the formula C_XH₈O₄. If 0.015 mol of the compound has a mass of 1.98 g, determine the value of X, per formula unit of the molecule. Take the atomic mass of carbon, oxygen, and hydrogen (g/mol) as 12, 16, and 1.0, respectively.

Ans: X = 5 carbon atoms

Molar mass = 1.98/0.015 = 132 g/mol

X = (132-72)/12 = 5

3. Given that one molecule of an organic compound with the empirical formula CH₂O has a mass of 2.0 × 10^–22 g, determine the molecular formula of the compound. Take the atomic mass of carbon, oxygen, and hydrogen (g/mol) as 12, 16, and 1.0, respectively, and Avogadro’s number as 6.0 × 10²³.

Ans: C₄H₈O₄

Molar mass = 2.0 × 10^–22 × 6.0 × 10²³ = 120 g/mol

n = 120/30 = 4; Hence molecular formula = C₄H₈O₄

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1. Given Avogadro’s number as 6.02 × 10²³, what is the mass present in 1.51 × 10²³ molecules of benzaldehyde, C₇H₆O? Take the atomic mass (g/mol) of C, H, and O as 12.0, 1.00, and 16.0, respectively.

Ans: 26.5 g

Molecular mass of benzaldehyde = 106 g

Number of moles = 1.51 × 10²³ / 6.02 × 10²³ = 0.25 moles

Mass of benzaldehyde = 0.25 × 106 = 26.5

2. Determine the sum of the stoichiometric coefficients of all reactants and products present in a balanced equation of the reaction: SiO₂ + HF → SiF₄ + H₂O

Ans: 8

SiO₂ + 4HF → SiF₄ + 2H₂O

3. How many sigma and pi bonds each are present in methanal?

Ans: 1 pi bond and 3 sigma bonds

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Identify the following species found on the Periodic Table given the information below:

1. Mass number 33; neutron number 18; number of electrons 18

Ans: P^3–

2. Mass number 55; neutron number 30; number of electrons 22

Ans: Mn³⁺

3. Mass number 66; neutron number 36; number of electrons 28

Ans: Zn²

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1. Determine the percentage of phosphorus present in phosphorus pentoxide (P₂O₅) given the relative atomic masses of phosphorus and oxygen as 31 and 16, respectively.

Ans: 44 %

Molar mass of (P₂O₅) = 142                          percentage of P = 62/142 × 100 = 44%

2. Determine the percentage of chromium present in the chromium oxide Cr₂O₃, given the relative atomic masses of chromium and oxygen as 52 and 16, respectively.

Ans: 68 %

Molar mass of (Cr₂O₃) = 152                        percentage of P = 104/152 × 100 = 68%

3. Determine the percentage of chlorine present in dichlorine hexoxide (Cl₂O₆) given the relative atomic masses of Chlorine and oxygen as 35 and 16, respectively.

Ans: 42 %

Molar mass of (Cr₂O₃) = 166                        percentage of P = 70/166 × 100 = 42%

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1. Calculate the number of moles of hydrogen gas released when 6.0 moles of Aluminium react with excess hydrochloric acid.

Ans: 9.0 moles

2Al + 6HCl → 2AlCl₃ + 3H₂

2. Determine the sum of the stoichiometric coefficients of all reactants and products in a balanced equation of the reaction: SiCl₄ + H₂O → SiO₂ + HCl

Ans: 8

SiCl₄ + 2H₂O → SiO₂ + 4HCl

3. Which nuclear species is formed when carbon-14 is bombarded with a proton to produce nitrogen-14?

Ans: Neutron

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Give the name of the major product formed in each of the following reactions

1. The Reaction of benzene with chlorine in the presence of aluminium chloride

Ans: chlorobenzene

2. The reaction of 2-methylpropane with a limited amount of chlorine gas

Ans: 2-chloro-2-methyl propane

3. The reaction of butanoic acid and methylamine

Ans: N-methyl butanamide

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During the production of pure iron, Fe₂O₃ reacts with carbon monoxide, CO, according to the reaction: Fe₂O₃ + 3CO → 2Fe + 3CO₂

1. Given that 80 g of Fe₂O₃ and 84 g of CO react, determine which reactant is the limiting reagent and by what amount. You are given the molecular mass of Fe₂O₃ and CO as 160 and 28 g/mol, respectively.

Ans: Fe₂O₃, limited by 0.50 mol

n Fe₂O₃ = 80/160 = 0.50 mol        n CO = 84/28 = 3.0 mol

n Fe₂O₃ required = 1/3 × 3.0 mol = 1.0 mol; but only 0.50 mol present

2. Given that 80 g of Fe₂O₃ and 84 g of CO react, determine which reactant is in excess and by what amount. You are given the molecular mass of Fe₂O₃ and CO as 160 and 28 g/mol, respectively.

Ans: CO, excess by 1.5 mols

n Fe₂O₃ = 80/160 = 0.50 mol        n CO = 84/28 = 3.0 mol

n CO required = 3/1 × 0.50 mol = 1.5 mol;    but 3.0 mol present

3. How many grams of iron will be produced from the reaction of excess Fe₂O₃ and 84 g of CO? You are given the molecular mass of Fe₂O₃ and CO as 160 and 28 g/mol, respectively, and the atomic mass of Fe as 56 g/mol.

Ans: 112 g

n CO = 84/28 = 3.0 mol  n Fe = 2/3 × 3.0 mol = 2.0 mol

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1. How many moles of phosphorus is present in 14.2 g of P₄O₁₀? Take the atomic mass (g/mol) of phosphorus and oxygen as 31 and 16, respectively.

Ans: n(P) = 0.20 mol

n(P₄O₁₀) = 14.2/284 = 0.050 mol; P = 4 × 0.05 = 0.20 mol

2. Determine the sum of the stoichiometric coefficients of all reactants and products present in a balanced equation of the reaction: C₃H₈ + O₂ → CO₂ + H₂O

Ans: 13

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

3. How many unpaired electrons are present in the molecule NO?

Ans: one (1)

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Write the equilibrium constant expression Kc for the following reversible reactions:

1. CH₄ (g) + H₂S (g) ⇌ CS₂ (g) + 4H₂ (g)

Ans: Kc =  [CS₂] [H₂]⁴ / [CH₄] [H₂S]

2. 2 Pb(NO₃)_{2 (s)} ⇌ 2 PbO _(s) + 4 NO₂ (g) + O₂ (g)

Ans: Kc =  [NO₂]⁴ [O₂]

3. N₂H₄ (g) + 6H₂O₂ (g) ⇌ 2NO₂ (g) + 8H₂O (g)

Ans: Kc = [NO₂]² [H₂O]⁸ / [N₂H₄] [H₂O₂]⁶

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1. What mass of methanoic acid is required to completely neutralise a solution made of 50.0 cm3 of 0.200 moldm^-3 NaOH? Take atomic mass (g/mol) of C as 12; O as 16; H as 1.0.

Ans: 0.46 g

Moles of NaOH = 0.20 moldm^-3 × 0.050 dm³ = 0.010 mol = moles of HCOOH

Mass of HCOOH needed = 46 × 0.010 = 0.46 g

2. Calculate the mass of solid that remains when 200 cm³ solution of Na₂CO₃ of concentration 0.25 moldm^-3 is heated to dryness. Take the atomic mass (g/mol) of Na as 23; O as 16; and C as 12

Ans: 5.3 g

Moles of Na₂CO₃ = 0.20 × 0.25 = 0.050 mol

Molar mass = 106 g/mol.        Hence mass present = 0.050 × 106 = 5.3 g

3. What mass of Na₂SO₄ must be dissolved in 100 cm3 of solution to obtain a concentration of 0.50 moldm^-3? Atomic mass (g/mol) of Na = 23; O = 16; S = 32

Ans: 7.1 g

Moles of Na₂SO₄ = 0.10 × 0.50 = 0.050 mole

Mass of Na₂SO₄  = 0.050 × 142 = 7.1 g

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1. Upon combustion, 0.40 g of a hydrocarbon produces 1.1 g of carbon dioxide. Determine the percentage composition of carbon in the compound. (C = 12; O=16, H = 1.0)

Ans: 75 %

Mass of C = 12/44 × 1.1 = 0.30 g

% C = 0.30/0.40 × 100 = 75 %

2. Determine the sum of the stoichiometric coefficients of all reactants and products present in a balanced equation of the reaction: Ag₂S → Ag + S₈

Ans: 25

8 Ag₂S → 16 Ag + S₈

3. Which of the hybrid orbitals in carbon has the highest percentage of s-character?

Ans: sp orbital (50%)

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Give the name of the major product formed from the reaction of HBr with each of the following:

1. 1-pentene

Ans: 2-bromopentane

2. 2-methyl-2-butene

Ans: 2-bromo-2-methylbutane

3. Cyclohexene

Ans: Bromo cyclohexane (or 1-bromocyclohexane)

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1. What mass of oxygen is needed to produce 90 g of water, given that an excess amount of hydrogen reacts? Take the atomic mass (g/mol) of H and O as 1.0 and 16, respectively.

Ans: 80 g

Mol of H₂O = 90/18 = 5.0 mol.

n O₂ = 5.0/2 = 2.5 mol                 Hence mass = 2.5 × 32 = 80 g

2. Determine the mass of Na₂CO₃ needed to produce 0.150 mol of carbon dioxide gas in a thermal decomposition reaction. Take the atomic mass (g/mol) of Na, C, and O as 23.0, 12.0, and 16.0, respectively.

Ans: 15.9 g

Molar mas of Na₂CO₃ = 106    since mole ratio is 1:1, mass = 106 × 0.150 = 15.9 g

3. Based on a reaction with solid carbon, determine the mass of oxygen needed to produce 16.8 g of carbon monoxide, given that oxygen is limited. Take the atomic mass (g/mol) of C and O as 12 and 16, respectively.

Ans: 9.6 g

Mol of CO = 16.8/28 = 0.60 mol           mol of O₂ = 0.60/2 = 0.30 mol

Mass of O₂ = 9.6 g

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1. Given Avogadro’s number as 6.0 × 10²³, how many atoms of oxygen are present in 4.0 moles of SO₃?

Ans: 7.2 × 10²⁴

Number of atoms = 6.0 × 10²³  × 4 mol × 3 O atoms = 7.2 × 10²⁴

2. Determine the sum of the stoichiometric coefficients of all reactants and products present in a balanced equation of the reaction: C₆H₈ + O₂ → CO₂ + H₂O

Ans: 19

C₆H₈ + 😯₂ →6CO₂ + 4H₂O

3. What is the maximum number of hydrogen bonds formed by a water molecule in ice?

Ans: four (4)

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Indicate the values of all quantum numbers permissible for the following orbitals

1. 4p

Ans: n = 4, l = 1, ml = -1, 0, +1

2. 3d

Ans: n = 3, l = 2, ml = -2, -1, 0, +1, +2

3. 5s

Ans: n = 5, l = 0, ml = 0

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1. Calculate the solubility in mg/dm³ of BaCrO4 at 25 °C given its solubility product is 1.0 × 10^–10. Take the molecular mass of BaCrO₄ as 253 g/mol.

Ans: 2.53 mg/dm³

Solubility = √1.0 × 10^–10 = 1.0 × 10^–5 mol/dm³

Solubility in mg/dm³ = 1.0 × 10^–5 × 253 × 1000 = 2.53 mg/dm³

2. Calculate the molar solubility of BaSO₄ in a 0.010 moldm³ solution of Ba(NO₃)₂ given that the solubility product of 1.1 × 10^–10.

Ans: 1.1 × 10^–8 mol/dm³

BaSO⁴  ⇌     Ba²⁺    +     SO₄^2–

0.01 + s

Solubility, s = 1.1 × 10^–10 / 0.010 = 1.1 × 10^–8 mol/dm³

3. Calculate the molar solubility of Cu(OH)₂ in a solution of pH 10. Solubility product of Cu(OH)₂ is 2.6 × 10^–19.

Ans: 2.6 × 10^–15 mol/dm3

OH– = 0.00010 mol/dm³

Cu(OH)₂  ⇌     Cu²⁺    +     2OH^–

2s + 0.00010

Solubility, s = 2.6 × 10^–19 / 0.00010 = 2.6 × 10^–15

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1. Determine the sum of the stoichiometric coefficients of all reactants and products present in a balanced equation of the reaction: Al + Fe₃N₂ → AlN + Fe

Ans: 8

2Al + Fe₃N₂ → 2AlN + 3Fe

2. Given that the atomic masses of manganese and astatine are 55 and 210, respectively, what mass of astatine will have the same number of particles as 2.2 g of manganese?

Ans: 8.4 g

Moles of Mg = 2.2/55.0 = 0.040

Hence equivalent mass of At = 0.040 × 210 = 8.4 g

3. To determine the formula of a hydrocarbon, 0.66 g of the hydrocarbon produced 2.2 g of carbon dioxide when burned. Determine the percentage composition of carbon in the compound. (C = 12; O= 16, H = 1.0)

Ans: 91 %

Mass of C = 12/44 × 2.2 = 0.60 g

% C = 0.60/0.66 × 100 = 91 %

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Indicate the cell notation for each of the following cell reactions

1. Cu_(s) + 2 Fe³⁺_(aq) → Cu²⁺_(aq)  + 2 Fe²⁺_(aq)

Ans: Cu | Cu²⁺ || Fe²⁺, Fe³⁺ | Pt

2. 2 Ag _(s) + 2 H⁺_(aq) → 2 Ag⁺_(aq)  + H_{2 (g)}

Ans: Ag | Ag⁺ || H⁺ | H₂ | Pt

3. 2 Cl^–_(aq) + 2 Fe³⁺_(aq) → Cl_{2 (g)} + 2 Fe²⁺_(aq)

Ans: Pt | Cl₂ | Cl^– || Fe²⁺, Fe³⁺ | Pt

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1. Determine the percent composition of carbon present in nicotine (C₁₀H₁₄N₂) given the relative atomic masses of carbon, hydrogen, nitrogen, and oxygen as 12, 1.0, 14, and 16, respectively.

Ans: 74 %

Molar mass of (C₁₀H₁₄N₂) = 162                  percentage of C = 120/162 × 100 = 74%

2. Determine the percent composition of carbon present in the alkaloid cytisine (C₁₁H₁₄N₂O) given the relative atomic masses of carbon, hydrogen, nitrogen, and oxygen as 12, 1.0, 14, and 16, respectively.

Ans: 69 %

Molar mass of (C₁₁H₁₄N₂O) = 190                               Percentage of C = 132/190 × 100 = 69%

3. Determine the percent composition of carbon present in the drug, pregabalin (C₈H₁₇NO₂), given the relative atomic masses of carbon, hydrogen, nitrogen, and oxygen as 12, 1.0, 14, and 16, respectively.

Ans: 60 %

Molar mass of (C₈H₁₇NO₂) = 159                 Percentage of C = 96/159 × 100 = 60 %

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1. Determine the sum of the stoichiometric coefficients of all reactants and products present in a balanced equation of the reaction: SiCl₄ + H₂O → H₄SiO₄ + HCl

Ans: 10

SiCl₄ + 4H₂O → H₄SiO₄ + 4HCl

2. Given that 0.20 moles of a compound A3B weighs 28 g, determine the atomic mass of element A if the atomic mass of element B is 14 g.

Ans: 42 g/mol

Molecular mass of compound = 28/0.2 = 140

Mass of element A = (140-14)/3 = 42 g/mol

3. What is the maximum number of hydrogen bonds formed by molecules of trimethylamine?

Ans: zero (0)

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The contact process for the manufacture of sulfuric acid involves the following equilibrium reaction: 2SO_{2 (g)} + O_{2 (g)} ⇌ 2SO3 _(g)        ΔH = –196 kJmol^–1

State and explain the effect of each of the following actions on the equilibrium of the reaction

1. An increase in pressure

Ans: Equilibrium will shift toward the formation of more product (right/forward)

An increase in pressure will favour the side with fewer moles of gas. Mole of reactants is 3 and moles of product is 2, hence pressure will favour formation of product/forward reaction

2. An increase in temperature

Ans: Equilibrium will shift toward the formation of more reactants (left/backwards)

Since the reaction is exothermic, an increase in temperature will favour the formation of reactants

3. A decrease in the amount of oxygen gas

Ans: Equilibrium will shift toward the formation of more reactants (left/backwards)

More SO₃ will break down to form O₂ in order to negate the effect of the reduced concentration of O₂.

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1. Ethyne reacts with oxygen in a ratio of 2:5. Calculate the enthalpy of bonds broken in this reaction. You are given the following bond energies in kJ/mol: C≡C = 840; C–H = 415; O=O = 500

Ans: 5840 kJ/mol

2 C≡C = 840 × 2 = 1680

4 C–H = 415 × 4 = 1660

5 O=O = 500 × 5 = 2500

Total bond energy = 5840 kJ/mol

2. Given that 4 moles of CO₂ and 2 moles of H₂O are produced from the reaction of ethyne and oxygen, calculate the enthalpy of bonds formed in the reaction. You are given the following bond energies in kJ/mol: C=O = 800; H–O = 460.

Ans: –8240 kJ/mol           (please ignore negative sign)

8 C=O = 800 × 8 = 6400

4 H–O = 460 × 4 = 1840

Total = 8240 kJ/mol

3. Nitrogen triiodide, NI₃, decomposes to form nitrogen gas and iodide. Calculate the enthalpy change for this reaction. You are given the following bond energies in kJ/mol: N–I = 160; N≡N = 950; I–I = 150

Ans: 620 kJ/mol

Bonds broken

3 N–I = 160 × 3 = 480

Bonds formed

N≡N = 950

I–I = 150

Enthalpy change = 1100 – 480 = 620 kJ/mol

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1. Determine the sum of the stoichiometric coefficients of all reactants and products present in a balanced equation of the reaction: FeS₂ + O₂ → Fe₂O₃ + SO₂

Ans: 25

4FeS₂ + 11O₂ → 2Fe₂O₃ + 8SO₂

2. Given the atomic masses of nitrogen, hydrogen, oxygen and cerium as 14, 1.0, 16, and 140, g/mol respectively, determine the mass of 1.0 mole of ammonium cerium (IV) nitrate, (NH₄)₂Ce(NO₃)₆

Ans: 546 g/mol

17×2 + 140 + 62×6 = 546 g/mol

3. Name the nuclide formed when Vanadium-52 undergoes a beta decay?

Ans: Chromium-52

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Refining petroleum helps to convert high molecular weight hydrocarbons into low molecular weight, high-octane products. Name one major reaction that occurs during the catalytic reforming of petroleum.

Ans:

• Dehydrogenation
• Isomerization
• Cyclization
• Aromatization
• Hydrocracking

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1. A molecule of an organic compound contains 8 carbon atoms, which account for a total of 60% of its molecular mass. Determine the molecular mass of the compound given that the atomic mass of carbon is 12.

Ans:160 g/mol

Total mass of Carbon = 12 × 8 = 98 g

Molecular Mass = (100 × 96) / 60 = 160 g/mol

2. A hydrocarbon contains 13 carbon atoms, which account for a total of 65 % of its molecular mass. Determine the molecular mass of the compound given that the atomic mass of carbon is 12.

Ans: 240 g/mol

Total mass of Carbon = 12 × 13 = 156 g

Molecular Mass = (100 × 156) / 65 = 240 g/mol

3. An aliphatic diol with molecular mass 174 g/mol contains 10 carbon atoms. Determine the number of hydrogen atoms present in the alcohol given that the atomic mass of carbon is 12, oxygen is 16, and hydrogen is 1.0

Ans: 22

Total mass of carbon = 12 × 10 = 120

Mass of oxygen = 16 × 2 = 32

Hence mass of H = 174 – 152 = 22

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1. How many moles of oxygen atoms are present in 2.4 g of S₂O₈? Take the atomic mass (g/mol) of Sulphur and oxygen as 32 and 16, respectively.

Ans: 0.10 mol

n(S₂O₈) = 2.4/192 = 0.0125 mol. n(O) = 8 × 0.0125 = 0.10 mol

2. The gaseous molecules: N₂O and CO₂ are mixed in a ratio of 1:3 by mass. What is the ratio of gases by volume? Take atomic masses of N, C and O as 14, 12 and 16, respectively.

Ans: 1:3

Molecular mass of N₂O = 44

Molecular mass of CO₂ = 44

Since molecular mass is the same, volume ratio will be the same, hence 1:3

3. Determine the sum of the stoichiometric coefficients of all reactants and products present in a balanced equation of the reaction: HNO₃ → H₂O + NO₂ + O₂

Ans: 11

4HNO₃ → 2H₂O + 4NO₂ + O₂        (Accept only integers)

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1. Which nuclear species is formed when boron-10 is bombarded with a proton to produce boron-8?

Ans: Tritium

2. Identify the nuclear species formed when oxygen-16 is bombarded with nitrogen-14 to produce fluorine-16

Ans: carbon-14

3. Identify the nuclear species formed when Neon-20 is bombarded with deuterium to produce an alpha particle.

Ans: Fluorine-18

4. Identify the nuclide formed when chlorine-33 undergoes a positron decay?

Ans: sulphur-33

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Given the following reduction enthalpies, write the standard cell notation for the cell reactions occurring and indicate the value of the emf.

1. Cu²⁺ / Cu      E⁰ = 0.337 V

Ag⁺ / Ag              E⁰ = 0.800 V

Ans: Cu | Cu²⁺ || Ag⁺ | Ag                      emf = 0.468 V

2. Sn²⁺ / Sn                      E⁰ = – 0.137 V

Fe³⁺ / Fe²⁺                        E⁰ = 0.770 V

Ans: Sn | Sn²⁺ || Fe²⁺, Fe³⁺ | Pt               emf = 0.907 V

3. Sn⁴⁺ / Sn²⁺                 E⁰ = 0.148 V

Pb⁴⁺ / Pb²⁺                       E⁰ = 1.667 V

Ans: Pt | Sn²⁺, Sn⁴⁺ || Pb⁴⁺, Pb²⁺ | Pt      emf = 1.519 V

4. Ti²⁺ / Ti                        E⁰ = – 0.163 V

U⁴⁺ / U³⁺                          E⁰ = – 0.609 V

Ans: Pt | U³⁺, U⁴⁺ || Ti²⁺| Ti                     emf = 0.446 V

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1. Given the atomic masses of magnesium, boron and oxygen as 24, 11, and 16 g/mol, respectively, determine the mass of 2.0 moles of magnesium borate, Mg₃(BO₃)₂

Ans: 380 g

24×3+59×2 = 190 g/mol

Mass of 2.0 moles = 190×2 = 380 g

2. Determine the maximum amount (in grams) of ammonia produced when 11.2 g each of hydrogen gas and nitrogen gas react according to the equation: N₂ + 3 H₂ ⇌ 2 NH₃

Take the atomic mass of nitrogen and hydrogen as 14.0 and 1.00, respectively.

Ans:13.6 g

N₂ + 3 H₂ ⇌ 2 NH₃

n(N₂) = 11.2/28 = 0.400 mole;     H₂ is in excess

mass of NH₃ = 0.400 × 17 × 2 = 13.6 g

3. Determine the sum of the stoichiometric coefficients of all reactants and products present in a balanced equation of the reaction: C₂H₂ + O₂ → CO₂ + H₂O

Ans: 13

2C₂H₂ + 5O₂ → 4CO₂ + 2H₂O

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1. What is the change in the oxidation state of the reducing agent present in the reaction: Cr(OH)3 + Br₂ → CrO₄^2– + Br^–

Ans: +3 to +6 (or a change of +3)

2. What is the oxidation state of the oxidised form of the reducing agent present in the reaction: Cr₂O₇^2- + C₂H₅OH → Cr³⁺ + CO₂

Ans: +4

3. How many moles of an ideal gas are present in 2.5 dm3 of gas at a temperature of 27 °C and 100 kPa? Take the molar gas constant to be 8.3 JK-1mol^-1

Ans: 0.10  mol

PV=nRT

Mole of gas = PV/RT = 100000 × 0.0025/(8.3 × 300) = 0.10 mol

4. 4.00 moles of a compound have a mass of 420 g. What is the molecular mass of the compound?

Ans: 105 g/mol

Molecular mass = 420/4.0 = 115 g/mol

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