You are Here: Home

# moles questions!!

1. hi i have been given some questions as homework and i am a bit stuck. if someone could help me with the first one i might understand it more.

given that the molecular weight of methylene blue is 374 what weight was dissolved in 1 litre of water to give a solution of 30 micro mol/litre?

if anyone could help i would greatly appreciate it!!!
2. maybe im confused, but 30 micromoles of methylene blue isn't it?

NB one micromole is moles i think...

3. From this formula you can work out the number of mols of solute in the solution, remember that

Now that you have the number of mols you can use the formula

This should give you the weight of the solute, which should be quite a small number, of the order of .
4. okay all of you are confusing me! i learnt it that moles was avogrado constant which means the amount of particles in a substance as in carbon atoms in exactly 12g of the carbon 12-isotope.
the formula is
n= m/Mr or n=c*v(in cm3)/1000 or c*v(dm3)
finally, n=v(dm3)/24.0 or n=v(cm3)/24000
5. (Original post by Unique_Renee)
okay all of you are confusing me! i learnt it that moles was avogrado constant which means the amount of particles in a substance as in carbon atoms in exactly 12g of the carbon 12-isotope.
the formula is
n= m/Mr or n=c*v(in cm3)/1000 or c*v(dm3)
finally, n=v(dm3)/24.0 or n=v(cm3)/24000

All of what you have said here is true, but mostly irrelevant, you arn't being asked to calculate how many molecules of solvent there are, merely the weight of what has been dissolved. So basically, here is a full solution, because you are getting yourself confused:

Now that you have the number of mols:

Geddit?
6. (Original post by IChem)
All of what you have said here is true, but mostly irrelevant, you arn't being asked to calculate how many molecules of solvent there are, merely the weight of what has been dissolved. So basically, here is a full solution, because you are getting yourself confused:

Now that you have the number of mols:

Geddit?
Thanks for that

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: February 18, 2009
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:
Today on TSR

### Help!

Will Oxford nullify my offer?