Part IX Rate of Reaction

1.2 g of magnesium ribbon is allowed to react with excess dilute hydrochloric acid at room conditions. It takes 5 minutes for the effervescence to stop. What is the rate of formation of the gaseous product of this reaction?

(Relative atomic mass: Mg = 24.3; molar volume of gas at room temperature and pressure = 24.0 dm³ mol^‒1)

• A. 237 cm³ min^‒1

• B. 640 cm³ min^‒1

• C. 1185 cm³ min^‒1

• D. 1200 cm³ min^‒1

Above is a concentration-time graph of a reaction taking place in a closed container.

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)

When chlorine gas is allowed to dissolve in concentrated sodium hydroxide solution at 70°C, the following reaction occurs:

3Cl₂(g) + 6NaOH(aq) → 5NaCl(aq) + NaClO₃(aq) + 3H₂O(l)

If the rate of consumption of OH^‒(aq) is 0.003 mol dm^‒3 s^‒1, what is the rate of formation of Cl^‒(aq) under the same conditions?

• A. 0.0025 mol dm^‒3 s^‒1

• B. 0.0030 mol dm^‒3 s^‒1

• C. 0.0036 mol dm^‒3 s^‒1

• D. 0.0150 mol dm^‒3 s^‒1

In the graph below, curve X shows the results obtained when excess zinc granules are added to dilute hydrochloric acid in a conical flask connected to a gas syringe.

Which of the following changes made to the reaction would give curve Y?

• A. A less concentrated hydrochloric acid of the same volume is used.

• B. The reaction mixture is cooled.

• C. A larger mass of zinc granules is used.

• D. The same volume and concentration of ethanoic acid is used for the reaction with zinc.

Which of the following pairs of chemicals, upon mixing under the same temperature, has the lowest rate of gas formation?

• A. 0.05 g of magnesium powder and 50 cm³ of 0.5 M hydrochloric acid

• B. 0.05 g of magnesium powder and 100 cm³ of 0.5 M sulphuric acid

• C. 0.05 g of magnesium ribbon and 50 cm³ of 0.5 M sulphuric acid

• D. 0.05 g of magnesium ribbon and 100 cm³ of 0.5 M hydrochloric acid

A teacher estimated the mass of zinc required for an experiment studying the rate of the following reaction:

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

The teacher would use a 100 cm³ gas syringe and 25 cm³ of 0.50 M hydrochloric acid. What was the maximum mass of zinc required, so that the volume of gas produced would not exceed 100 cm³?

(Relative atomic mass: Zn = 65.4; molar volume of gas at room temperature and pressure = 24.0 dm³ mol^‒1)

• A. 0.22 g

• B. 0.27 g

• C. 0.31 g

• D. 0.41 g

A student carried out two experiments to investigate the rate of reaction between dilute hydrochloric acid and calcium carbonate. The table above summarizes the reaction conditions for each experiment.

The reaction took place in a closed flask and the variation of the gaseous pressure inside the flask was measured with time. Which of the following graphs correctly represents the experimental results?

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Consider the following reaction:

Cr₂O₇^2‒(aq) + 14H⁺(aq) + 3C₂O₄^2‒(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 C₂O₄^2‒(aq) in the same period of time?

• A. 1.42 mol dm^‒3 s^‒1

• B. 0.06 mol dm^‒3 s^‒1

• C. 2.05 × 10^‒6 mol dm^‒3 s^‒1

• D. 9.43 × 10^‒8 mol dm^‒3 s^‒1

12 cm³ of chlorine reacts with 42 cm³ of oxygen to form 12 cm³ of a gaseous oxide of chlorine. Which of the following is the molecular formula of this oxide?

(Assume that the volumes of gases are all measured at room temperature and pressure.)

• A. ClO

• B. Cl₂O

• C. Cl₂O₃

• D. Cl₂O₇

A student electrolysed 100 cm³ of 0.0100 M NaCl(aq) for a certain period of time until the concentration of NaCl(aq) became 0.0104 M. What was the mass of water electrolysed?

(Density of water = 1.0 g cm^‒3)

• A. 1.9 g

• B. 3.8 g

• C. 5.7 g

• D. 7.6 g