A research chemist is working on developing a catalytic electrode that makes possible the formation of methanol (CH3OH) in an electrolytic cell using carbon dioxide from the air - VCE - SSCE Chemistry - Question 6 - 2008 - Paper 1
Question 6
A research chemist is working on developing a catalytic electrode that makes possible the formation of methanol (CH3OH) in an electrolytic cell using carbon dioxide ... show full transcript
Worked Solution & Example Answer:A research chemist is working on developing a catalytic electrode that makes possible the formation of methanol (CH3OH) in an electrolytic cell using carbon dioxide from the air - VCE - SSCE Chemistry - Question 6 - 2008 - Paper 1
Step 1
Give a balanced equation for the complete combustion of methanol with oxygen.
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Answer
The balanced equation for the complete combustion of methanol (CH3OH) with oxygen (O2) is:
the value in kJ mol-1, and sign, of ΔH for the reaction you have written.
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The enthalpy change (ΔH) for the complete combustion of methanol is approximately -1450 kJ mol-1. The negative sign indicates that the reaction is exothermic.
Step 3
Calculate the amount of electricity, in coulomb, that passes through the cell.
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To calculate the amount of electricity (Q) that passes through the cell, we can use the formula:
Calculate the mass, in grams, of methanol that forms during that time, assuming that all the electricity that passes through the cell is used to produce methanol.
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To find the mass of methanol (CH3OH) produced, we first determine the moles of methanol that can be formed. From the reaction at the cathode:
For the formation of 1 mole of CH3OH, 6 moles of electrons are required. The total charge (Q) in coulombs allows us to find the number of moles of electrons:
ext{Number of moles of electrons} = rac{Q}{F} = rac{2,201,280}{96500} ext{ moles}
Then, the moles of CH3OH produced are:
ext{Number of moles of } CH3OH = rac{ ext{moles of electrons}}{6}
To find the mass:
Molar mass of CH3OH = 32.04 g/mol
Thus,
Step 5
Given that the experimental readings of current, time and mass of methanol obtained are accurate, give one reason why the amount of methanol is lower than predicted.
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One possible reason for the lower yield of methanol than predicted could be evaporation or losses during the transfer and collection process. Some methanol might escape before it can be measured, affecting the overall yield.
