Identify and explain the functions of a thistle funnel and a dropping funnel. For the decomposition of lead(II) nitrate, write the balanced equation and describe a method to separate NO2 from O2.

Here are the solutions to the questions:

Question 1:

• A thistle funnel has a long stem and an open top, used to add liquids to a reaction vessel without a stopcock, often extending below the liquid surface to prevent gas escape.
• A dropping funnel has a stopcock to control the rate of liquid addition drop-wise, and its stem typically ends above the liquid surface.

Question 2:

a)

Step 1: Write the balanced chemical equation for the thermal decomposition of lead(II) nitrate.

$$\boxed{\text{2Pb(NO}_3)_2\text{(s)} \xrightarrow{\Delta} \text{2PbO(s)} + \text{4NO}_2\text{(g)} + \text{O}_2\text{(g)}}$$

b)

• Nitrogen(IV) oxide ($\text{NO}_2$) can be separated from oxygen ($\text{O}_2$) by cooling the mixture. At low temperatures, $\text{NO}_2$ dimerizes to form colourless liquid dinitrogen tetroxide ($\text{N}_2\text{O}_4$), while oxygen remains a gas. The liquid $\text{N}_2\text{O}_4$ can then be separated.

Question 3:

a)

• The litmus solution turns red.

b)

• Sulphur(IV) oxide ($\text{SO}_2$) is an acidic gas. When bubbled through water, it reacts to form sulphurous acid ($\text{H}_2\text{SO}_3$), which is acidic and turns litmus red. $$\text{SO}_2\text{(g)} + \text{H}_2\text{O(l)} \rightleftharpoons \text{H}_2\text{SO}_3\text{(aq)}$$

Question 4:

a)

• The method of separation illustrated is Distillation.

b)

• Mixture M is likely a solution of a non-volatile solid in a liquid or a mixture of two miscible liquids with different boiling points.

c)

• An application is the purification of water (separating water from dissolved salts).

Question 5:

a) When hydrogen sulphide gas is bubbled into concentrated nitric(V) acid:

• Observation: A yellow precipitate (sulfur) is formed, and brown fumes (nitrogen dioxide) are observed.
• Explanation: Hydrogen sulphide ($\text{H}_2\text{S}$) is oxidized to sulfur, while concentrated nitric(V) acid ($\text{HNO}_3$) is reduced to nitrogen dioxide. $$\text{H}_2\text{S(g)} + \text{2HNO}_3\text{(aq)} \longrightarrow \text{S(s)} + \text{2NO}_2\text{(g)} + \text{2H}_2\text{O(l)}$$

b) When hydrogen sulphide gas is bubbled into freshly prepared iron(III) chloride solution:

• Observation: The brown/yellowish-brown solution turns pale green, and a yellow precipitate (sulfur) is formed.
• Explanation: Iron(III) ions ($\text{Fe}^{3+}$) are reduced to iron(II) ions ($\text{Fe}^{2+}$), and hydrogen sulphide ($\text{H}_2\text{S}$) is oxidized to sulfur. $$\text{2FeCl}_3\text{(aq)} + \text{H}_2\text{S(g)} \longrightarrow \text{2FeCl}_2\text{(aq)} + \text{S(s)} + \text{2HCl(aq)}$$

Question 6:

a)

• Water hardness is caused by the presence of dissolved calcium ions ($\text{Ca}^{2+}$) and magnesium ions ($\text{Mg}^{2+}$).

b)

• One method to remove permanent hardness is the washing soda method (adding sodium carbonate).

c)

• One advantage of drinking hard water is that it provides essential calcium and magnesium ions for healthy bones and teeth.

Question 7:

• The sample was pure water.
• Reason: The heating curve shows a sharp and constant melting point at $0^\circ\text{C}$ and a sharp and constant boiling point at $100^\circ\text{C}$. Impure substances melt and boil over a range of temperatures.