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A student set up the following experiment to model a process and observed the colour change of the crystals - HSC - SSCE Chemistry - Question 33 - 2011 - Paper 1
Question 33
A student set up the following experiment to model a process and observed the colour change of the crystals. Copper(II) sulfate pentahydrate crystals in watch glass... show full transcript
Worked Solution & Example Answer:A student set up the following experiment to model a process and observed the colour change of the crystals - HSC - SSCE Chemistry - Question 33 - 2011 - Paper 1
Step 1
Identify liquid X and explain the colour change of the crystals. Include a chemical equation in your answer.
Answer
Liquid X can be identified as water (H₂O). When Copper(II) sulfate pentahydrate (CuSO₄·5H₂O) is exposed to water, it undergoes hydration. The colour change of the crystals from blue to a lighter blue occurs because the hydrated form of Copper(II) sulfate absorbs water, forming more hydrated ions. The chemical equation for this process is:
Step 2
Why are the large volumes of CO₂(g) produced during the Solvay process of little environmental concern? Include chemical equations in your answer.
Answer
The large volumes of CO₂(g) produced during the Solvay process are of little environmental concern due to the relatively small contribution of industrial processes to overall greenhouse gas emissions. Additionally, the CO₂ produced can be largely recycled and utilized in other chemical processes.
The chemical equations demonstrating the production of CO₂ in the Solvay process are:
- Formation of sodium bicarbonate:
- Decomposition of sodium bicarbonate:
Step 3
Calculate the mass of calcium chloride produced per tonne of sodium chloride used in the Solvay process.
Answer
To calculate the mass of calcium chloride produced from sodium chloride in the Solvay process, we can use the stoichiometric equation involved in the process. The balanced equation is:
From the equation, 1 mole of CaCl₂ is produced from 2 moles of NaCl. The molar mass of NaCl is approximately 58.5 g/mol, and for CaCl₂ it is approximately 110.98 g/mol. For 1 tonne (1000 kg) of NaCl, we have:
Moles of NaCl = 1000 kg / (58.5 g/mol) = 17114.53 mol
Since 2 moles of NaCl yield 1 mole of CaCl₂, we have:
Moles of CaCl₂ = 17114.53 mol / 2 = 8557.27 mol
Mass of CaCl₂ = 8557.27 mol × 110.98 g/mol = 949,933.48 g or approximately 949.93 kg.
Step 4
Account for the observations at the anode and cathode. Include relevant chemical equations in your answer.
Answer
At the anode (positive electrode), oxidation occurs, producing oxygen gas, which causes bubbles. The relevant half-equation is:
At the cathode (negative electrode), reduction occurs. The hydrogen ions gain electrons to form hydrogen gas, leading to the observed bubbles. The relevant half-equation is:
The litmus paper at the anode turns red indicating acidic conditions due to the generation of H⁺ ions, whereas the litmus paper at the cathode turns blue indicating alkaline conditions due to the production of hydroxide ions (OH⁻).
Step 5
What is the difference between the electrolytic cell described above and a galvanic cell, in terms of energy requirements?
Answer
An electrolytic cell requires an external source of energy to drive the chemical reactions, as it involves non-spontaneous processes. In contrast, a galvanic cell generates electrical energy from spontaneous chemical reactions. In a galvanic cell, the chemical energy produced from the redox reactions is converted into electrical energy, allowing it to operate without an external power source.