[eoerex]

Hi everyone, I'm having trouble with this question:

"Calculate the number of moles required to make 250ml of 100mM KMnO₄
Give your answer in moles to two significant figures omitting the units"

I didn't do A-Level chemistry only Biology, and I've watched a few videos and read a few articles on how to get the atomic mass etc and it's embarrassing as to why I don't quiet know what this question is asking of me. I know the molecular mass is 158.

I'm sorry to ask such a basic question. one part that i'm confused upon is the 100mM is that 0.1?

Any help would be very much appreciated as I also need to answer the sister question which is
"Now that you know how many moles of KMnO₄ are required and you know the molecular mass, you should your previous answers to calculate what mass of KMnO₄ you require to make 250ml of 100 mM"

thank you for your time and again, any help would be so very much appreciated 

Kindest regards
Ade

[Hunter2]

Answer:

1. What is molar mass of KMnO₄
2. Do you know what does mM means?

If you can answer this. Then you can calculate the sister question.

[eoerex]

Answer:

1. What is molar mass of KMnO₄
2. Do you know what does mM means?

If you can answer this. Then you can calculate the sister question.

I think by what I'm reading, is that the molar mass is 158.03395g being - K:39.0983 Mn:54.93805 O:15.9994

But What does mM mean then? this is where I'm confused 

Thank you for your reply though, sorry I'm a mature student and trying to get my mind around it having not done it before.

[Hunter2]

ok 1. Answer is correct

for second one. M is equal molarity. Do you know what that menas and what unit it has?
and the samll m in mathematics. What does mm, ml, mg, etc. means.

[eoerex]

ok 1. Answer is correct

for second one. M is equal molarity. Do you know what that menas and what unit it has?
and the samll m in mathematics. What does mm, ml, mg, etc. means.

Ah, ok thank you, well I'm not sure what M exactly means and certainly not when it is mM, i understand that measurements of mm, ml, mg, so m would be meters? Or am I being horrendously dense minded? 

Thank you

[Hunter2]

M = Molarity. Its the moles in 1 liter solution.  m = milli = 0.001

1 mM = 0.001 mol/l

So how much would be 100 mM?

[eoerex]

M = Molarity. Its the moles in 1 liter solution.  m = milli = 0.001

1 mM = 0.001 mol/l

So how much would be 100 mM?

Oh ok, thank you Hunter2. So would I be right in saying 100mM is 0.1 mol/l?

[Hunter2]

Yes correct and now you can answer the original question. How many moles you need for 250 ml and also answer the sister question.

[eoerex]

Yes correct and now you can answer the original question. How many moles you need for 250 ml and also answer the sister question.

Thank you Hunter2, I really appreciate your *delete me*

[Hunter2]

What is the result.

[eoerex]

What is the result.

Ok right, so I think without hopefully being too embarrassed about getting it wrong, but, theres 0.25 mol/l required for the 1st question and then is it the mass 158.03395 x the mol/l = 39.5084875g?

[Hunter2]

No....calculate again.

How it can be 0,25 mol/l if you have only 0,1 mol/l. Check also units its alo wrong.

[eoerex]

No....calculate again.

How it can be 0,25 mol/l if you have only 0,1 mol/l. Check also units its alo wrong.

Sorry, grrr, I'm getting confused again, so is it 0.025 mols? I'm clearly not understanding the question perhaps? Sorry for being dense

[Hunter2]

yes 0.025 mol so how much the other values.