[flaren5]

Hi all, I was wondering if anyone had any insight into the following problem:  Thank you!!

In anticipation to the building of a permanent colony on the moon, scientists are planning to provide a self-sustaining source of oxygen by extracting it out of lunar rocks (which are composed primarily of silica). Thus, both silicon (Si(s)) and oxygen gas (O2(g)) can be produced by the electrolysis of molten silica (SiO2(l)). (Note:  in the liquid state, SiO2 can be considered as a mixture of Si4+ and 2 O2- ions)  Hint:  O2 + 4e- → 2O2-

a.  Write both half-reactions involved in this process, identifying the oxidation and reduction half reactions.  Also, write the balanced equation describing the global reaction.

b.  How many hours are required to convert 1.00 x 103 kg of SiO2(l) by passing a constant current of 5.00 x 104 A through the melt?

c.   How many litres of O2(g) will be obtained from this process (at 25 °C and 1 atm)?

d.  The O2(g) produced is compressed into a 100 L gas tank.  If the temperature on the moon reaches 107 °C during the day, what will be the pressure inside the gas tank (assume that ideal gas conditions apply here)?

[Jack Bauer]

Hi all, I was wondering if anyone had any insight into the following problem:  Thank you!!

In anticipation to the building of a permanent colony on the moon, scientists are planning to provide a self-sustaining source of oxygen by extracting it out of lunar rocks (which are composed primarily of silica). Thus, both silicon (Si(s)) and oxygen gas (O2(g)) can be produced by the electrolysis of molten silica (SiO2(l)). (Note:  in the liquid state, SiO2 can be considered as a mixture of Si4+ and 2 O2- ions)  Hint:  O2 + 4e- → 2O2-

Just quickly as I am a touch busy now..

a.  Write both half-reactions involved in this process, identifying the oxidation and reduction half reactions.  Also, write the balanced equation describing the global reaction.

For an electrochemical cell something has to be reduced and something has to be oxidised.

You know you want O2 gas so first oxidation must be 2O2- > O2 + 4e-   Think about what else you have and you will figure out what is being reduced easy enough.

b.  How many hours are required to convert 1.00 x 103 kg of SiO2(l) by passing a constant current of 5.00 x 104 A through the melt?

Faraday constant = 96 485.3415 C / mol  gives the charge past during the reduction or oxidation of a mole of a substance when one electron is transfer.

c.   How many litres of O2(g) will be obtained from this process (at 25 °C and 1 atm)?

Volume of a mole of gas at those conditions is?

d.  The O2(g) produced is compressed into a 100 L gas tank.  If the temperature on the moon reaches 107 °C during the day, what will be the pressure inside the gas tank (assume that ideal gas conditions apply here)?

This one is just about given to you, have a think.

[flaren5]

Thank you very much for taking the time, it's most certainly appreciated...
I believe that you have provided enough guidance for me to work through the problem...

[Jack Bauer]

np, good luck.

[flaren5]

I still seem to be stumped with part c.)....I think I figured out part b.) i got an answer of 1.25x10^-6 s?

Does anyone have any suggestions on how to proceed with part c?

Thank you

[Jack Bauer]

assuming it is ideal

1 mole of any gas occupies 22.4 dm3 at stp (standard temperature and pressure, taken as 0°C and 1 atmosphere pressure). You may also have used a value of 24.0 dm3 at room temperature and pressure (taken as about 20°C and 1 atmosphere).

http://www.chemguide.co.uk/physical/kt/idealgases.html

Your answer for b seems very fast, but then it does say a current of 5.00 x 104 A which is massive accounting for the small time needed....you sure this number is correct?  Also, did you account for the 4 electrons?