When doing mole problems, are answers that vary slightly acceptable?

_Redzer_

I've been doing some mole questions and I've been used to being told to just round off the molecular weights, like carbon would be 12 instead of 12.011, oxygen would be 16, etc.

Problem is, when I go back to check if my answer is right, I'm off by a few digits. I've tried it both ways, doing it exactly and rounding off, but I'm still usually .1-10 digits off my lecturer's answers.

Does it matter in the exam if I'm off that much, or do I need to be dead-on accurate, even if I'm doing it properly?

I don't get how my answers are differing to his, tbh.

citrus burst

In terms of exams, most examiners are more interested in your approach and reasoning than your final answer. If you do the question correctly and show logic and explain how you got to your result, you will get >75% of the marks available. If the desired answer is 3.4 and you calculate 3.3 or 3.6 then I wouldn't really worry about it. The reasoning being that after a few decimal places it becomes meaningless. What I would make sure of is you get your order of magnitude right. If the answer is 78 and you calculate 0.0000065 then I would be worried as this shows a lack of understanding.

In terms of why your answers might be varying from his there are a couple of reasons; calculator used, constants, rounding etc. all of these will combine to add small discrepancies that will add up and cause a small amount of error in an answer.

_Redzer_

Alright thanks for clearing that up. I have a bit of a problem here trying to get this one to work, though.

The active agent in many bleaches is potassium hypochlorite (KOCl). It can be manufactured in a two-stage process which involves making chlorine (Cl2) and then passing it into a hot solution of potassium hydroxide (KOH):

MnO2 + 4HCl -> MnCl2 + Cl2 + 2H2O Cl2 +2KOH -> KCl+KOCl+H2O

(a) What volume of Cl2 (at STP) would be required to produce 20 kg of potassium hypochlorite?

(b) What mass of MnO2 would be required to produce 20 kg of potassium hypochlorite?

(c) Calculate the overall mass of water produced when the same amount of KOCl
is prepared.

I got A to work out which gave me 4,977.8 L, but I can't seem to get B to work, even though I'm using the same formula as I did with other problems.

I get the MM of MnO2 -87g/mol and KOCl -90g/mol, I then dived 87/90 and multiply the result by 1000 to get the answer like I did in other problems.

I end up with 966.7kg, but that's impossible as I only have 20kg to work from.

Any advice to sort it out?

*In previous problems I'd be working from a total weight of 1 tonne, maybe that explains why I'd have to multiple by 1000 to get the answer? I'm not sure.

mocker2012

Do you have the numerical answers by any chance?
I got for (a) 4947.5L (b) 19.2kg (c) 7.95kg but I don't know if they're right?