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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Answer
The value of ΔH for the complete combustion of methanol is approximately -1450 kJ mol−1. The negative sign indicates that the reaction is exothermic, releasing energy.
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 use the formula:
Q=Iimest
where:
I = current in Amperes (25.5 A)
t = time in seconds (24.0 hours = 24.0 × 3600 seconds = 86400 s)
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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From the balanced reaction, 1 mole of methanol (CH3OH) requires 6 moles of electrons. Therefore, using Faraday's law, we can find the mass of methanol produced:
Calculate moles of electrons:
ext{Moles of } e^- = rac{Q}{F} ext{, where } F ext{ (Faraday's constant)} ext{ is approximately } 96500 ext{ C/mol.} ext{Moles of } e^- = rac{2.20 imes 10^6 ext{ C}}{96500 ext{ C/mol}} ext{ }
ightarrow ext{ approximately } 22.8 ext{ moles.}
Moles of methanol produced:
ightarrowextapproximately3.81extmoles.
Mass of methanol:
Molar mass of methanol (CH3OH) = 32.04 g/mol.
ightarrow ext{ approximately } 122 g.$$
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 than predicted amount of methanol is the occurrence of side reactions such as evaporation. During the electrolysis process, some of the methanol may evaporate or escape the system, leading to a lower yield of the product.
