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chemistry igcse acapprinted 18 · PDF 18
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For an element, it is the same as the relative atomic mass written in grams.
• For a compound it is the same as the relative formula mass or relative molecular mass in
grams.
Moles – Formulae and Questions
• The following are the formulas concerning moles that you need to know:
Q. Sodium hydrogencarbonate is found in baking powder.
When sodium hydrogencarbonate is heated it forms three products.
2NaHCO3 → Na2CO3 + H2O + CO2
Calculate the volume of carbon dioxide formed at room temperature and pressure when
12.6 g of NaHCO is heated using the following steps:
● Determine the molecular mass of one mole of NaHCO3
= 23+1+12+3(16)
= 36+48 = 84
● Calculate the number of moles of NaHCO3 used
● Determine the number of moles of carbon dioxide formed
(Look at the ratios in the balanced reaction given in the question)
= NaHCO3 :
CO2
=
2
:
1
=
0.015
:
x
2x = 0.015
x = 0.075 mol. of CO2
● Calculate the volume of carbon dioxide formed at room temperature and pressure.