You are Here: Home

# GCSE Qs - Reacting Amount Calculations watch

1. Please can you help me? I have tried to work this out, but keep getting wrong answers, which are different from the ones at the back of the CPG workbook.

How much aluminium oxide would be needed to make the following amounts of aluminium?

a) 1kg b) 2kg c) 4.5 kg d) 1 tonne (1000 kg)

Thanks!
2. molar ratio of aluminium oxide to aluminium is 1:2,

mol of aluminium for 1kg = mass/molar mass = 1000g/27 g mol^-1 = 37.04 mol

therefore mol of aluminium oxide = 0.5 x 37.04 = 18.52 mol

hence mass = mol x molar mass of aluminium oxide
= 18.52 x 102 = 1889.04g = 1.89 kg (3SF)

for the other parts, simply work out what fraction they are of 1kg and multiply appropriately to get those answers. hope that helped!
3. All in kilograms yea...
From equation ratio of Al to Al2O3 is 4:2 = 2:1 (therefore multiply moles of Al my .5)
a) (1/27) = number of moles of Aluminium
Moles of Al2O3 = 1/54
Mass of Al2O3 = (1/54)*RMM of Al2O3 = (1/54)*102 = 17/9 Kg
If you do the same thing for all the masses then it should be fine.... is that answa right?
4. (Original post by mackin boi)
All in kilograms yea...
From equation ratio of Al to Al2O3 is 4:2 = 2:1 (therefore multiply moles of Al my .5)
a) (1/27) = number of moles of Aluminium
Moles of Al2O3 = 1/54
Mass of Al2O3 = (1/54)*RMM of Al2O3 = (1/54)*102 = 17/9 Kg
If you do the same thing for all the masses then it should be fine.... is that answa right?
yeah that works, but surely to be correct you must convert from kg to g, because the molar masses are in g mol^-1, even though the factor of 1000 cancels out at the end?
5. Yep, thanks! You're right
6. (Original post by moojoo)
yeah that works, but surely to be correct you must convert from kg to g, because the molar masses are in g mol^-1, even though the factor of 1000 cancels out at the end?
i was always taught to just forget the factor because it takes up time in the xam....and it sort of complicates it ... s'all gud
7. kool, yeah that's fair enough i suppose it does take time

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: June 14, 2005
The home of Results and Clearing

### 3,019

people online now

### 1,567,000

students helped last year
Today on TSR

### Took GCSEs this summer?

Fill in our short survey for Amazon vouchers!

### University open days

1. Bournemouth University
Wed, 22 Aug '18
2. University of Buckingham
Thu, 23 Aug '18
3. University of Glasgow