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Answer parts (a) and (b) of the question on pages 2–4 of the Section II Writing Booklet - HSC - SSCE Chemistry - Question 31 - 2018 - Paper 1
Question 31
Answer parts (a) and (b) of the question on pages 2–4 of the Section II Writing Booklet. Start each part of the question on a new page. (a) (i) Use a labelled diagr... show full transcript
Worked Solution & Example Answer:Answer parts (a) and (b) of the question on pages 2–4 of the Section II Writing Booklet - HSC - SSCE Chemistry - Question 31 - 2018 - Paper 1
Step 1
(a) (i) Use a labelled diagram to show the structure of a soap molecule.
Answer
The structure of a soap molecule can be represented as follows:
O
||
H2C -- C -- O−
/ \
C C
// \
C C
\ /
C ---- C
| |
CH3 CH3
In this diagram, the left part represents a polar hydrophilic head that interacts with water, while the long right chain symbolizes the non-polar hydrophobic tail that interacts with grease and oil.
Step 2
(a) (ii) Explain how soap acts as a cleaning agent.
Answer
Soap acts as a cleaning agent through its unique molecular structure that has both polar and non-polar components. When soap is mixed with water, the polar hydrophilic head aligns with the water molecules, while the non-polar hydrophobic tail attaches to grease or oil particles.
As a result, soap molecules aggregate around the grease, forming structures called micelles. This allows the grease to be suspended in water, enabling it to be washed away. The cleaning effectiveness is due to this duality, making soap essential for emulsifying oily substances.
Step 3
(b) (i) Relate a property of sulfuric acid to a condition necessary for its safe transport and storage.
Answer
Concentrated sulfuric acid is highly hygroscopic, meaning it readily absorbs water from the environment. This property necessitates that it be transported and stored in airtight containers to prevent it from absorbing moisture. If sulfuric acid absorbs water, it can result in exothermic reactions, posing safety risks such as spills or container failure.
Step 4
(b) (ii) Explain the observations that could be made in the investigations.
Answer
In the first investigation, when sulfuric acid acts as an oxidising agent, it will react with a metal like magnesium (Mg). This reaction would produce hydrogen gas with observable effervescence:
ightarrow ext{MgSO}_4 + ext{H}_2$$ The metal will oxidize, causing a color change in the solution, indicating the reaction. In the second investigation, when sulfuric acid behaves as a dehydrating agent, it would remove water from a substance such as sugar, leading to a blackening effect due to carbon formation: $$ ext{C}_{12} ext{H}_{22} ext{O}_{11} ightarrow 12 ext{C} + 11 ext{H}_2 ext{O}$$ This observation would show the effectiveness of sulfuric acid in dehydrating agents.Step 5
(c) (i) Justify TWO conditions that could change the colour of the solution from pink to blue.
Answer
-
Change in Temperature: Increasing the temperature of the reaction will shift the equilibrium to the right, according to Le Chatelier's principle, favoring the formation of the [CoCl4]2− complex, which has a blue color.
-
Change in Concentration: Adding chloride ions (Cl−) to the system will also shift the equilibrium to the right, resulting in increased production of the blue [CoCl4]2− complex. More Cl− ions will compete with water molecules for cobalt ions, effectively changing the color.
Step 6
(c) (ii) Determine the equilibrium concentration of HI for this reaction.
Answer
Given the reaction:
With an equilibrium constant, K, of 64, we start by setting up the ICE (Initial, Change, Equilibrium) table:
-
Initial concentrations:
- [H2] = 0.20 M
- [I2] = 0.20 M
- [HI] = 0 M
-
Change will be represented as:
- [H2] = 0.20 - x
- [I2] = 0.20 - x
- [HI] = 2x
The equilibrium expression is:
K = rac{[ ext{HI}]^2}{[ ext{H}_2][ ext{I}_2]}
Substituting values into the expression:
64 = rac{(2x)^2}{(0.20 - x)(0.20 - x)}
Assuming x is small: 64 = rac{(2x)^2}{0.20^2}
Calculating:
This leads to:
ightarrow x ext{ (approx)} = 1.13$$ Finally, The equilibrium concentration of HI: $$[HI] = 2x = 2(0.32) = 0.64 ext{ M}$$Step 7
(d) Explain how the environmental issues associated with the industrial production of sodium hydroxide and sodium carbonate can be addressed.
Answer
The production of sodium hydroxide typically occurs through the chloralkali process. This process generates chlorine gas and has environmental concerns, such as discharges of hazardous by-products.
One way to mitigate these effects includes utilizing a diaphragm cell that minimizes the release of chlorine gas into the environment. Additionally, waste products can be treated to neutralize any harmful chemicals before disposal.
Furthermore, sodium carbonate is produced from limestone, which avoids excessive mining impacts, and can use brine solutions that capture waste and recycle in the process:
ightarrow CaO (s) + CO_2 (g)$$ The environmental impact can be reduced significantly by ensuring that these processes can re-utilize valuable by-products and minimize emissions.