# Chemistry Homework Help - Moles

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#1
Calcium oxide, CaO, is used for making cement which is widely used in the construction industry. Calcium oxide can prepared as ‘quicklime’ by heating limestone in a lime kiln to about 550oC. The calcium carbonate in the limestone decomposes into calcium oxide and carbon dioxide:
CaCO3 → CaO + CO2
Calculate the mass of CaO that could be made from limestone containing 20 tonnes of CaCO3.

I got 11200000g. Please can someone check that is right, as I think I have done something wrong.
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1 year ago
#2
I don’t have a calculator on me atm so I can’t physically work out the answer but this is the way I would do it:

Work out the moles of CaCO3 (moles = mass/Mr) and then as it’s 1:1 the moles of CaCO3 will equal the moles of CaO and then you can work out the mass of CaO by using mass =moles x Mr. Also check what units the question asks you to provide the answer if 20 tonnes = 20,000 Kg (if u didn’t already know)
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1 year ago
#3
I got 11,205,742 g but that is probably due to me using molar masses with 4 decimals. As long as you calculated your result the way cath_slater already described, your answer should be correct.
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#4
(Original post by kitkathilein)
I got 11,205,742 g but that is probably due to me using molar masses with 4 decimals. As long as you calculated your result the way cath_slater already described, your answer should be correct.
Yes that is what I got I just put it to 3s.f for ease. Thank you.
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1 year ago
#5
(Original post by izaakha)
Calcium oxide, CaO, is used for making cement which is widely used in the construction industry. Calcium oxide can prepared as ‘quicklime’ by heating limestone in a lime kiln to about 550oC. The calcium carbonate in the limestone decomposes into calcium oxide and carbon dioxide:
CaCO3 → CaO + CO2
Calculate the mass of CaO that could be made from limestone containing 20 tonnes of CaCO3.

I got 11200000g. Please can someone check that is right, as I think I have done something wrong.
The thermal decomposition of CaCO3 only really gets going at about 840 oC.

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#6
(Original post by Pigster)
The thermal decomposition of CaCO3 only really gets going at about 840 oC.

It will still occur though; just not as fast. My teacher has a PhD in chemistry - I think she knows what she is talking about.
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1 year ago
#7
(Original post by izaakha)
It will still occur though; just not as fast. My teacher has a PhD in chemistry - I think she knows what she is talking about.
ooh fancy schmancy
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1 year ago
#8
(Original post by izaakha)
It will still occur though; just not as fast. My teacher has a PhD in chemistry - I think she knows what she is talking about.
Actually at temperatures much below my stated temperature, delta G becomes positive, so decomposition will no longer be feasible, i.e. the reaction is impossible. It isn't a rates issue, but one of the interplay between enthalpy and entropy changes.

If you drop the air pressure, then the minimum temperature that the reaction happens at will drop, but I don't think even a vacuum would drop it as far as 550 oC (I can't be bothered to do the calc).

Tell her to put that in her pipe and smoke it.

PhD smeehachdee.
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