Chemistry help!

because it is in proportion, whatever the answer in grams is for 297 g will be the answer in kg for 297 kg

I still don't quite understand. Do you mean to say 297000g? Also, the molar mass is grams per mole so I don't get how you can do 297kg divided by 146.1grams per mole - the units are not the same.

They’re not doing 297 kg / 141.6 g

They’re doing 297 g / 141.6 g

The answer would be multiplied by 1000 to get the result for 1000 times the amount they have calculated, but then to get the result in kg you would just have to divide it by 1000 again, so they didn’t bother

ok keep it in g until the end then.

297,000 g / (M_r) 146.1 = 2,033 moles of SF₆ reacted (4 s.f.)

As stoichiometric ratio is 8:1, then (8 x 2,033) moles Li reacted

= 16,260 moles Li reacted (4 s.f.)

As moles = mass (g) / M_r then, moles x M_r = mass (g)

16,260 x 6.9 = 112,200 g (4 s.f.), therfore;

Ans = 112 kg (3 s.f.)

Thanks! So here's what I've got so far:
297g/141.6g -->2moles
therefore 297g=2moles
(muliply result by 1000times) 297000g=2000moles
297kg=2000moles?

No - I just meant at the beginning. You still have to do the rest of the calculation like the other poster

You answer needs to be in kilograms but because you are using moles you are doing your working in grams. They have just not shown all their working in the mark scheme.

It just doesn't seem to make sense Could you please show me your working if possible?
Btw thanks for your help anyways

OK I’ll give it a try don’t worry, I used to hate methods like this too

1 kg = 1000g

So to work out how much lithium you need for 297 kg, you’re working out how much lithium you need for 297000 g of SF6.

But that’s a big number, so if you work out how much lithium you need for 297 g of SF6, you can then multiply it by 1000 at the end.

It just so happens that this question wants the answer in kg. So once you’ve found the answer at the end, you need to put it in kg

So you divide it by 1000 again

Instead of doing that, the mark scheme has just said, let’s assume that whatever the answer is for 297 (g) is also the answer for 297 kg

they can ignore the units in this case because the number that’s valid if you assume everything is in grams, is also valid if you assume everything is in kilograms.

If you converted into grams (ie multiplied by 1000) first and then back into kg at the end, you still did it right.

In fact I would argue yours is the more conscientious method as it’s easy to confuse units in general and forget to convert