What is equilibrium? What would be observed when hydrochloric acid is added drop-wise to a solution of Bismuth chloride?

The diagram shows dilute hydrochloric acid (HCl) reacting with Iron (II) Sulphide (FeS).

When a metal sulphide reacts with an acid, hydrogen sulphide gas is produced.

Gas X is hydrogen sulphide.

i) Name gas X.

• Gas X is Hydrogen Sulphide.

ii) Write equation for the reaction.

iii) Explain why it is not advisable to use concentrated sulphuric(IV) acid to dry the gas.

• Hydrogen sulphide ($\text{H}_2\text{S}$) is a reducing agent. Concentrated sulphuric acid ($\text{H}_2\text{SO}_4$) is a strong oxidizing agent. They would react, oxidizing the hydrogen sulphide and thus not effectively drying it.

Question 9:

a) What is equilibrium?

• Equilibrium is a state in a reversible reaction where the rate of the forward reaction is equal to the rate of the reverse reaction, and the concentrations of reactants and products remain constant.

b)

i) What would be observed when hydrochloric acid is added drop-wise to a solution of Bismuth chloride?

• The white suspension of bismuth oxychloride ($\text{BiOCl(s)}$) would dissolve or disappear.

ii) Give a reason for the observation in b (i).

• Adding hydrochloric acid ($\text{HCl}$) increases the concentration of a product. According to Le Chatelier's principle, the equilibrium $\text{BiCl}_3\text{(aq)} + \text{H}_2\text{O(l)} \rightleftharpoons \text{BiOCl(s)} + \text{2HCl(aq)}$ shifts to the left (reverse reaction) to consume the added $\text{HCl}$, causing the solid $\text{BiOCl}$ to react and dissolve.

Question 10:
State the colour of the indicators in the solutions given in the table.

• (i) Blue
• (ii) Red
• (iii) Colourless
• (iv) Pink

Question 11:

a) Name the:

i) Colourless gas.

• From Step I: Copper (II) oxide + Carbon powder $\longrightarrow$ Colourless gas + Brown solid. $$\text{CuO(s)} + \text{C(s)} \longrightarrow \text{Cu(s)} + \text{CO(g)}$$ The colourless gas is carbon monoxide.
• Carbon monoxide

ii) Brown solid.

• From Step I: The brown solid is copper.
• Copper

iii) Brown gas.

• From Step II: Brown solid (Copper) + Brown gas $\longrightarrow$ Blue solution. Copper reacts with nitric acid to form a blue solution (copper(II) nitrate) and nitrogen dioxide (a brown gas).
• Nitrogen dioxide

b) Write the equation for the reaction in step I.

Question 12:

a) Name process A.

• Process A is the conversion of Petroleum to Ethene ($\text{CH}_2=\text{CH}_2$). This process is called cracking.
• Cracking

b) Identify substances Q, R and S.

• Q: Ethene ($\text{CH}_2=\text{CH}_2$) reacts with concentrated sulphuric acid and water to form Q. This is the hydration of ethene to ethanol. $$\text{CH}_2=\text{CH}_2 + \text{H}_2\text{O} \xrightarrow{\text{Conc. H}_2\text{SO}_4} \text{CH}_3\text{CH}_2\text{OH}$$ Q is Ethanol.
• R: Q (Ethanol) reacts with sodium ($\text{Na}$) to produce hydrogen gas ($\text{H}_2$) and R. $$\text{2CH}_3\text{CH}_2\text{OH} + \text{2Na} \longrightarrow \text{2CH}_3\text{CH}_2\text{ONa} + \text{H}_2$$ R is Sodium ethoxide.
• S: Q (Ethanol) undergoes a reaction with excess concentrated sulphuric acid at $170^\circ\text{C}$ to form S. This is the dehydration of ethanol to ethene. $$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{Excess H}_2\text{SO}_4, 170^\circ\text{C}} \text{CH}_2=\text{CH}_2 + \text{H}_2\text{O}$$ S is Ethene.

Question 13:
State one use of each of the acids given to complete the table:

• The table for question 13 is not provided in the image. Assuming the question refers to common acids or acids mentioned in the paper (e.g., Hydrochloric acid, Sulphuric acid, Nitric acid):
  • Hydrochloric acid (HCl): Used for cleaning metal surfaces (pickling).
  • Sulphuric acid (H₂SO₄): Used in car batteries or for the production of fertilizers.
  • Nitric acid (HNO₃): Used in the production of fertilizers or explosives.