A) State and explain the observations made. b) Write an equation for the reaction between chlorine and dilute sodium hydroxide solution.

Question 8:

a) State and explain the observations made.

• Observations: The greenish-yellow colour of chlorine gas disappears. The litmus paper is bleached (turns colourless).
• Explanation: Chlorine gas reacts with dilute sodium hydroxide solution to form sodium chloride, sodium hypochlorite, and water. Sodium hypochlorite is a bleaching agent, which causes the litmus paper to lose its colour. $$\text{Cl}_2\text{(g)} + \text{2NaOH(aq)} \longrightarrow \text{NaCl(aq)} + \text{NaClO(aq)} + \text{H}_2\text{O(l)}$$

b) Write an equation for the reaction between chlorine and dilute sodium hydroxide solution.

Question 9:

a) Define rate of reaction.

• The rate of reaction is the change in concentration of a reactant or product per unit time.

b)

i) On the axes below, sketch the curve obtained when mass of flask and contents is plotted against time. Label this curve A.

ii) On the same axes, draw and label as B, the curve that would have been obtained if powdered calcium carbonate of same mass had been used.

• The reaction is $\text{CaCO}_3\text{(s)} + \text{2HCl(aq)} \longrightarrow \text{CaCl}_2\text{(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}$.
• Since the flask is open, the mass of the flask and contents decreases as $\text{CO}_2$ gas escapes.
• Curve A (marble chips): The mass decreases over time and then levels off when the reaction stops.
• Curve B (powdered calcium carbonate): Powdered calcium carbonate has a larger surface area, so the reaction rate is faster. The mass will decrease more rapidly (steeper slope) but will level off at the same final mass as curve A, because the same mass of $\text{CaCO}_3$ is used, producing the same total amount of $\text{CO}_2$.

      ^ Mass of flask and contents (g)
      |
      | \
      |  \  B (Powdered CaCO3)
      |   \
      |    \   A (Marble chips)
      |     \
      |      \
      |       \
      |        -----------------
      +--------------------------------> Time (s)

Question 10:

a) State the observations made in test-tubes A and B.

• Test-tube A: Effervescence (fizzing/bubbling) is observed.
• Test-tube B: The calcium hydroxide solution turns milky/cloudy.

b) Write equations for the reactions taking place in test-tubes A and B.

• Test-tube A: $$\boxed{\text{Na}_2\text{CO}_3\text{(aq)} + \text{2HCl(aq)} \longrightarrow \text{2NaCl(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}}$$
• Test-tube B: $$\boxed{\text{CO}_2\text{(g)} + \text{Ca(OH)}_2\text{(aq)} \longrightarrow \text{CaCO}_3\text{(s)} + \text{H}_2\text{O(l)}}$$

c) State and explain the observations made in test-tube B if the reaction is allowed to continue for a long time.

• Observation: The milky/cloudy solution becomes clear again.
• Explanation: The insoluble calcium carbonate ($\text{CaCO}_3$) reacts with excess carbon dioxide ($\text{CO}_2$) and water to form soluble calcium hydrogencarbonate ($\text{Ca(HCO}_3)_2$). $$\text{CaCO}_3\text{(s)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)} \longrightarrow \text{Ca(HCO}_3)_2\text{(aq)}$$

Question 11:
Draw and name all the possible isomers of compound $\text{C}_4\text{H}_9\text{Br}$.
There are four isomers:

1. 1-bromobutane $$\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{Br}$$
2. 2-bromobutane $$\text{CH}_3-\text{CH}_2-\text{CH(Br)}-\text{CH}_3$$
3. 1-bromo-2-methylpropane $$\text{CH}_3-\text{CH(CH}_3)-\text{CH}_2-\text{Br}$$
4. 2-bromo-2-methylpropane $$\text{CH}_3-\text{C(Br)(CH}_3)-\text{CH}_3$$

Question 12:

a)

i) State what was observed when barium nitrate was added to the mixture.

• A