What is the empirical formula of a hydrocarbon with 75 % carbon and 25 % hydrogen by mass?

A. C₃H

B. CH₂

C. C₂H₆

D. CH₄

D

Well answered and straight forward.

A sample of a compound contains approximately 24.0 g C, 3.0 g H, and 1.6 g O. What is the empirical formula of the compound?

A.  C₂₀H₃₀O

B.  C₈₄H₁₀O₆

C.  C₂H₃O

D.  C₂₄H₃₀O₂

A

How many moles of magnesium hydroxide are produced with 0.50 mol of ammonia?

Mg₃N₂ (s) + 6H₂O (l) → 3Mg(OH)₂ (aq) + 2NH₃ (aq)

A. 0.25

B. 0.33

C. 0.75

D. 1.5

C

90 % of the candidates were able to deduce the amount of a product given the amount of another product and the balanced equation.

What volume of carbon dioxide, CO₂ (g), can be obtained by reacting 1 dm³ of methane, CH₄ (g), with 1 dm³ of oxygen, O₂ (g)?

CH₄ (g) + 2O₂ (g) → CO₂ (g) + 2H₂O (l)

A. 0.5 dm³

B. 1 dm³

C. 2 dm³

D. 6 dm³

A

The concept of using volume ratios of gases as mole ratios in balanced equations was well answered.

3.00 mol of C₃H₈ is mixed with 20.00 mol of O₂. Which quantity is present at the end of the reaction?

C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O (g)

A.  1.00 mol of C₃H₈

B.  5.00 mol of O₂

C.  12.00 mol of CO₂

D.  16.00 mol of H₂O

B

What is the pressure, in Pa, inside a 1.0 m³ cylinder containing 10 kg of H₂ (g) at 25 ºC?

R = 8.31 J K^–1 mol^–1; pV = nRT

A. $\frac{1\times {10}^4\times 8.31\times 25}{1.0\times {10}^3}$

B. $\frac{5\times {10}^2\times 8.31\times 298}{1.0}$

C. $\frac{1\times 8.31\times 25}{1.0\times {10}^3}$

D. $\frac{5\times {10}^3\times 8.31\times 298}{1.0}$

D

Which solution neutralizes 50.0 cm³ of 0.120 mol dm^–3 NaOH (aq)?

A. 12.5 cm³ of 0.080 mol dm^–3 H₃PO₄

B. 25.0 cm³ of 0.120 mol dm^–3 CH₃COOH

C. 25.0 cm³ of 0.120 mol dm^–3 H₂SO₄

D. 50.0 cm³ of 0.060 mol dm^–3 HNO₃

C

Which diagram represents a heterogeneous mixture?

A

A few G2 forms suggested that candidates could have chosen A or B. However, homogeneous and heterogeneous mixtures are usually represented in such a way while only option A shows a clear separation in the mixture. We will avoid schematic diagrams in the future for this type of questions.

What is the sum of the integer coefficients when propene undergoes complete combustion?

__C₃H₆ (g) + __O₂ (g) → __CO₂ (g) + __H₂O (l)

A. 11

B. 17

C. 21

D. 23

D

93 % of the candidates balanced the equation for the combustion of propene and obtained the sum of the integer coefficients.

How much ethanol contains 1.20 × 10²⁴ atoms of carbon?

Avogadro’s constant, L or N_A: 6.02 × 10²³mol⁻¹

A.  0.333 mol

B.  0.500 mol

C.  1.00 mol

D.  2.00 mol

C

A compound with M_r = 102 contains 58.8 % carbon, 9.80 % hydrogen and 31 % oxygen by mass.
What is its molecular formula?

A_r: C = 12.0; H = 1.0; O = 16.0

A. C₂H₁₄O₄

B. C₃H₄O₄

C. C₅H₁₀O₂

D. C₆H₁₄O

C

What is the volume of gas when the pressure on 100 cm³ of gas is changed from 400 kPa to 200 kPa at constant temperature?

A. 50.0 cm³

B. 100 cm³

C. 200 cm³

D. 800 cm³

C

85 % of the candidates were able to deduce the new volume of a sample of gas after the pressure was halved. The most commonly chosen distractor was the value that assumed a direct proportionality between volume and pressure.

0.02 mol of zinc is added to 10.0 cm³ of 1.0 mol dm^–3 hydrochloric acid.

Zn (s) + 2HCl (aq) → ZnCl₂(aq) + H₂(g)

How many moles of hydrogen are produced?

A.  0.005

B.  0.01

C.  0.02

D.  0.04

A

Higher scoring candidates managed to estimate moles of gas produced in the reaction of zinc with hydrochloric acid solution.

2.67 g of lead (II) carbonate is decomposed by heating until constant mass.

PbCO₃(s) → PbO (s) + CO₂(g)

What is the final mass of solid?

A.  0.44 g

B.  2.23 g

C.  2.67 g

D.  3.11 g

B

76% of candidates correctly identified final mass of solid in the decomposition reaction with little difficulty in using mental math to arrive at the answer.