# C3.1.6 Moles, need help!

Been stuck on this for ages, and its due in tomorrow haha, any help?

Calcium carbonate breaks down on heating to produce calcium oxide and carbon dioxide gas. CaCO3 CaO CO2
A student heats 15 g of calcium carbonate strongly in a crucible.

Relative atomic masses (Ar): Ca 40, C 12, O 16.

a Calculate the number of moles in 15 g of calcium carbonate. (2 marks)

b Use your answer to part a to determine the number of moles of calcium oxide that will be produced. (1 mark)

c Calculate the mass of calcium oxide produced by this reaction. (2 marks)

4 A student is preparing a sample of sodium nitrate, NaNO3. She mixes 17 g of sodium oxide with an excess of nitric acid.
The equation for the reaction is: Na2O 2HNO3 2NaNO3 H2O

Relative atomic masses (Ar): Na 23, O 16, N 14, H 1.

a Calculate the number of moles in 17 g of sodium oxide. (2 marks)

b Calculate the maximum mass of sodium nitrate that can be produced in this reaction. (3 marks)

5 Aluminium and iron oxide (Fe2O3) react together to produce aluminium oxide (Al2O3).
The equation for the reaction is: 2Al Fe2O3 Al2O3 2Fe

Relative atomic masses (Ar): Al 27, O 16, Fe 56.

Calculate the mass of iron that is produced by reacting 20 g of iron oxide with an excess of aluminium.
the way i was taught moles is through the equation:

mass = moles x Mr
(which i remember through Mr mole lives in his hole)

mass
Mr x moles

for
a. you would find the Mr of calcium carbonate (100), and you have been given the mass which is 15. so you would do moles = mass/Mr, moles = 15/100 , moles = 0.15

b. for b, i would assume you use a ratio to solve it. in the equation there are no big numbers in front of any of the compounds meaning that the CaCO3 and CaO is a 1:1 ratio which means there is 0.15 moles which are produced.

c. we take the 0.15 moles from the previous question and use it in the equation above. so we work out the Mr (40 + 16 = 56), and do the equation: mass = Mr x moles, mass = 56 x 0.15, mass = 8.4g
4 A student is preparing a sample of sodium nitrate, NaNO3. She mixes 17 g of sodium oxide with an excess of nitric acid.
The equation for the reaction is: Na2O 2HNO3 2NaNO3 H2O

Relative atomic masses (Ar): Na 23, O 16, N 14, H 1.

a Calculate the number of moles in 17 g of sodium oxide. (2 marks)

for this question use the same equation, moles = mass/mr
moles = 17 / ((23x2) + 16)
moles = 0.27

b Calculate the maximum mass of sodium nitrate that can be produced in this reaction. (3 marks)

equation that needs to be used is mass= mr x moles
we can work out the moles by a ratio, Na2O is represented by 1, and because 2NaNO3 has a 2 in front of it, it is a 1:2 ratio meaning we have to multiply 0.27 by 2 which = 0.54 moles
we then calculate the Mr = (2 x 23) + (2 x 14) + (16 x 6) = 170 (remember everything is multiplied by 2 because of the big number at the front)
we now do: 170 x 0.54 = 91.8g