moles and concentrations

[mollykins]

I have two questions i hope someone will check, to see if i'm doing them right, please;

1)what volume of 0.1m of sulfuric acid contains 0.002 moles

would the answer be, 98 (the relative molecular mass) x 0.002 , then either divided or multiplied by 0.1?

2) 4.24g of Na2CO3 is dissolved in water and the solution is made up to 250ml. what is the concentration of the solution in mol dm^-3 ?

would you, say there's 106g in 1dm^-3 (or 1 mol), then divide that by 4.24 to get 25 mol dm^-3, then divide that by 40 to find the mol dm^-3 ? which I make to be 0.625 mol dm^-3 ????????????????????

[mollykins]

Plus, if you have to claculate the concentration in moles dm^-3, and you're given the moles and in how many dm^3, you times 1 by the dm^3 then divide (by 5 if it's 0.2 moles for example) to find the answer. Or do you need to use the relative molecular mass?

[Dris]

SB baits her all the time -I wouldnt have been able to bite my tonque for as long as Molly has.
I cant inderstand nor fathom why peeps like SB dont just avoid Mollys threads -hey its not rocket science:)
Cant help Molly -its like a foreign language to me-wheres Factor 30 when you need him/her.Theres a fair few who KNOW what youre posting about and are generally very helpful.
Take it Mike took a side swipe for kudos against a 17yr old girl? Hi 5 big man !!!!

[mike11111]

Pardon me for breathing! Anyway, I've worked out one chemical equation: Molly (and her fan club) + humour = 0.

[jomifl]

Ratter, were you really a professional mole trapper? I used to do a bit of amateur mole trapping, what kind of traps did you use?

[Dris]

You're pardoned Mike:)

[jomifl]

Molly, Question 1 ..I don't think you need bring in the molecular weight of sulfuric acid, it is just a question of proportions.

[jomifl]

molly question 2.. you need to divide the weight of sodium carbonate by the molecular weight to find out how many moles you have. when this is dissolved, how many moles would there be in a litre.

[Calibax]

I agree jomifl, a litre of a 0.1 molar solution of ANYTHING contains 0.1 moles so you can work out what volume contains 0.002 moles

[mollykins]

Helen 1) I get a lot of homework, msot of which I don't have a problem with and 2) I'm not asking people to do it for me, i'm just checking my answers.

[mollykins]

Thanks jom and cali

[mollykins]

So would I divide 0.1 by 0.002 ? or the other way round?

[jomifl]

Molly ..Just think about it..If 1litre contains 0.1 mole then 0.002 moles will be in a lot less than a litre. As I said before it is a question of proportion or ratio. Which calculation gives the most sensible answer?

[mollykins]

Thanks jom, once you think about it and get your head around what the proportions must be, it's obvious.

[mollykins]

jom, one more thing, if the question asks about concentration, then you do have to use the RMM don't you?

thanksss

[jomifl]

Molly are you refering to Q 2?