25-minute Test : Part IX Rate of Reaction

1.20 g of magnesium ribbon is added to excess dilute hydrochloric acid at room conditions. The effervescence stops after five minutes. What is the rate of formation of hydrogen for the reaction?

Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

(Relative atomic mass: Mg = 24.3; molar volume of gas at room temperature and pressure = 24 dm³ mol⁻¹)

• A. 237 cm³ min⁻¹
• B. 474 cm³ min⁻¹
• C. 1185 cm³ min⁻¹
• D. 1200 cm³ min⁻¹

Consider the following reaction:

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

Which of the following methods CANNOT be used to follow the progress of the reaction in the school laboratory?

(1) Measuring changes in mass of the reaction mixture

(2) Measuring changes in volume of the gaseous product

(3) Measuring changes in pressure of the reaction system

• A. (1) only
• B. (2) only
• C. (1) and (3) only
• D. (2) and (3) only

The concentration-time graph for a reaction taking place in a closed container with a fixed volume under certain conditions is shown on the left. Which of the following equations correctly represents the reaction?

• A. P(g) → Q(g)
• B. 2P(g) → 3Q(g)
• C. 3P(g) → 2Q(g)
• D. 2Q(g) → 3P(g)

Two trials of an experiment were performed to study the factors that affect the rate of reaction between limestone and hydrochloric acid. The graph on the left shows the experimental results. The two trials were differed by only one condition and excess hydrochloric acid was used. Which of the combinations about the conditions of the two trials is correct?

• A
• B
• C
• D

What is the maximum volume of CO₂(g) produced, measured at room temperature and pressure, when 1 g of CaCO₃(s) reacts with 20.0 cm³ of 2 M HCl(aq)?

CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + CO₂(g) + H₂O(l)

(Relative atomic masses: C = 12.0, O = 16.0, Ca = 40.1; molar volume of gas at room temperature and pressure = 24 dm³ mol⁻¹)

• A. 120 cm³
• B. 240 cm³
• C. 480 cm³
• D. 960 cm³

An experiment was carried out to study the kinetics of the reaction between sodium thiosulphate solution and dilute hydrochloric acid at a certain temperature.

Na₂S₂O₃(aq) + 2HCl(aq) → 2NaCl(aq) + S(s) + SO₂(g) + H₂O(l)

10 cm³ of 2.0 M HCl(aq) were separately added to four beakers each containing Na₂S₂O₃(aq) prepared by mixing different concentrations and volumes of Na₂S₂O₃(aq) with water as shown in the table. The average rate of the reaction can be determined by measuring the time needed for ‘blotting out’ the cross. Given that the reaction rate depends on both the concentrations of Na₂S₂O₃(aq) and HCl(aq). In which of the beakers does the reaction take the shortest time to ‘blot out’ the cross?

• A. P

• B. Q

• C. R

• D. S

Two trials of an experiment were carried out to investigate the kinetics of reaction between calcium carbonate and dilute hydrochloric acid. The chemicals used are listed in the table while the other experimental conditions were the same. The reaction occurred in a closed flask with a fixed volume and the pressure of the reaction system was measured at regular time intervals in each trial. Which of the graphs best represents the experimental results?

• A
• B
• C
• D

Consider the following reaction:

Cr₂O₇²⁻(aq) + 14H⁺(aq) + 3C₂O₄²⁻(aq) → 2Cr³⁺(aq) + 6CO₂(g) + 7H₂O(l)

If the pH of the reaction mixture increases from 4.1 to 4.4 in 90 seconds, what is the rate of consumption of C₂O₄²⁻(aq) at this time interval?

• A. 0.06 mol s⁻¹
• B. 0.06 mol dm⁻³ s⁻¹
• C. 9.43 × 10⁻⁸ mol s⁻¹
• D. 9.43 × 10⁻⁸ mol dm⁻³ s⁻¹

An experiment was conducted to study the rate of the reaction between magnesium and dilute hydrochloric acid under certain conditions. The graph on the left shows the volume of hydrogen produced at regular time intervals. The tangent to the curve at time t = 0 is given. What is the initial rate of the reaction with respect to the volume of hydrogen produced under the experimental conditions?

• A. 0.14 cm³ s⁻¹
• B. 7.30 cm³ s⁻¹
• C. 16.7 cm³ s⁻¹
• D. 23.0 cm³ s⁻¹

A gaseous mixture consists of methane and ethane with a volume ratio of 2 : 1. It needs 300 cm³ of oxygen for complete combustion. What is the volume of methane in the mixture?

• A. 20 cm³
• B. 40 cm³
• C. 60 cm³
• D. 80 cm³