How do I work out the mass of a chemical, given how much I use of a different chemical?

Question

There's just a few questions I'm stuck with, here when I was revising my Chemistry - please can you show your working, too!

Thanks

a) What mass of CO2 is formed from 100g of CaCO3?
b) What mass of CaO is formed from 1g of CaCo3?
c) What mass of CaCO3 must have reacted to produce 88g CO2?

Finally, and thanks guys, there's this...

If the RMM of any gas occupies 24L [1L = 1dm3], determine the mass of CaCo3 which must have decomposed to produce 156dm3 of CO2.

Anonymous · Accepted Answer

it's rather easy. first you always have to write down the balanced equation of the reaction going on.

CaCO3 ----> CaO + CO2
i assumed the reaction is the combustion of CaCO3

thus you can see the mole reaction is 1 : 1 : 1

a) mass of CO2 = 100/ (40.07 +12+48)  x (12 + 32)
=43.7g 
what i am doing above is first, i find out the moles of CaCO3 used [100/ (40.07 +12+48], then using hte mole value, i multiply by the molecular mass of CO2 to get mass of CO2.

)b mass of CaO = 1/ (40.07 +12+48) x (40.07 + 12)
=0.517g

it is similar for part b.

for part c, it is the same really.

c) mass of CaCO3 = 88 / (12+32) x (40.07 + 12 + 48)
=200.14g

i find out the mole of CO2 then use it to calculate the mass of CaCO3.

The last part is just that you need to use a different unit to calculate moles ie you're using DM3 to calculate. it is similar to part C of this question.

Moles of CO2 = 156/24
=6.5
mass of CaCO3 = 6.5 x (40.07 + 12 + 48)
=654.55g

there! hope this helps

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How do I work out the mass of a chemical, given how much I use of a different chemical?

1 Answer