Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Viral on September 24, 2009, 03:04:03 PM

Question: How much calcium oxide is produced by heating 25 tonnes of calcium carbonate?
Take Ar(CaO) to be 56 and Ar(CaCO3) to be 100.
My answer: 446429g. Is this correct?

No, explain your approach.

25 tonnes = 25,000,000g
25,000,000 / 100 = 250,000
100/56 = 25/14
25/14 * 250,000 = 446429g

Your answer is not in grams, not paying attention to units is a sure way to disaster. Ask Lockheed Martin about Mars Climate Orbiter if you don't believe.

Sorry, not sure what you mean =\ .
My friend got the answer 14010989.01g by doing 25,000,000 / 100.1 * 56.1 . Is that right?
Is there like a formula triangle for this?

Your friends approach is correct but the numeric answer in g wrong there is no way to give an answer with that accuracy from the data given.
The way to solve it by writing out the reaction equation and doing the simple maths with the data given.

Hmm, I still don#t understand. We can't use g as the unit?

OK lets do this very slowly for the very slow people out there.
There are 1000000g in 1tonne.
So if and only if the question said 25.0000000T as the start weight you could put the answer in g.
However given 25T as a start weight the answer should be in T anything else is false precision.
Given:
Take Ar(CaO) to be 56 and Ar(CaCO3) to be 100.
you should use that data not other data your friend has looked up.
Read the question and answer the question that has been set.
If you start with a reaction equation you'd see how wrong your original answer was.