1. Na₂S₂O₃ reacts with dilute HCl to give a pale yellow precipitate. If 1 cm³ of 0.1 mol dm^-3 HCl is added to 10 cm³ of 0.02 mol dm^-3 Na₂S₂O₃ the precipitate forms slowly.

If the experiment is repeated with 1 cm³ of 0.1 mol dm^-3 HCl and 10 cm³ of 0.05 mol dm^-3 Na₂S₂O₃ the precipitate forms more quickly.

Why is this?

2. A student investigates if, at 30^oC, the concentration of acid affects how rapidly it reacts with a known mass of magnesium.

The student has a beaker, concentrated acid, water and the apparatus below.

P a balance

Q a clock

R a measuring cylinder

S a thermometer

Which of these pieces of apparatus does the student use?

3. An acid-base indicator, HIn, dissociates according to the following equation.

            In(aq) ⇌  H+(aq) + In-(aq)

             colour A                 colour B

          Which statement about this indicator is correct?

I. In a strongly acidic solution colour B would be seen.

II. In a neutral solution the concentrations of HIn- (aq) and In (aq) must be equal.

III. It is suitable for use in titrations involving weak acids and weak bases.

4. The Haber process for the manufacture of ammonia is represented by the following equation.

N₂(g) + 3H₂(g) ⇌ 2NH₃(g)            ΔH = -92 kJ mol-1

Which statement is correct about this reaction when the temperature is increased?

5. Which statement about catalysts is correct for a typical equilibrium reaction?

6. In the reaction below

                                             N₂(g) + 3H₂(g) ⇌ 2NH₃(g)      ∆H = −92 kJ

          Which of the following changes will increase the amount of ammonia at equilibrium?

I.       Increasing the pressure

II.      Increasing the temperature

III.     Adding a catalyst

7. What will happen if CO₂(g) is allowed to escape from the following reaction mixture at equilibrium?

                        CO₂(g) + H₂O(l) ⇌ H⁺(aq) + HCO₃^– (aq)

8. In the last century the Haber process was sometimes run at pressures of 1000 atm and higher.

Now it is commonly run at pressures below 100 atm.

What is the reason for this change?

Consider the following equilibrium:

2NO_{2 (g)}   ⇌  N₂O_{4 (g)} + energy

The equilibrium will shift to the left as a result of……………………

10. Ethene, C₂H₄, can be produced in the following industrial system:

                     C₂H_{6  (g)} + energy ⇌  C₂H_{4 (g)} + H_{2 (g)}

The conditions that are necessary to maximize the equilibrium yield of C₂H₄ are…………………….