Results are out! Find what you need...fast. Get quick advice or join the chat
x

Unlock these great extras with your FREE membership

  • One-on-one advice about results day and Clearing
  • Free access to our personal statement wizard
  • Customise TSR to suit how you want to use it

Simple question

Announcements Posted on
Rate your uni — help us build a league table based on real student views 19-08-2015
  1. Offline

    ReputationRep:
    I dont understand the markscheme where i've put the part i don't understand in red.

    Specifically i dont get where 40 comes from?
    Click image for larger version. 

Name:	chem q.png 
Views:	53 
Size:	102.7 KB 
ID:	155703

    Thanks in advance .
  2. Offline

    ReputationRep:
    Moles of H2O2 in 250cm3 diluted is the same as the moles of H2O2 in 25cm3 of the original undiluted.

    The 40 comes from calculating the concentration (in dm3) of the H2O2 in 25cm3 by dividing by 25/1000.
    Dividing by 25/1000 is of course the same as multiplying by 40.

    When you have conc in mol per dm3 you multiply by the molar mass to find the mass per dm3.
  3. Offline

    ReputationRep:
    (Original post by Killjoy-)
    Moles of H2O2 in 250cm3 diluted is the same as the moles of H2O2 in 25cm3 of the original undiluted.

    The 40 comes from calculating the concentration (in dm3) of the H2O2 in 25cm3 by dividing by 25/1000.
    Dividing by 25/1000 is of course the same as multiplying by 40.

    When you have conc in mol per dm3 you multiply by the molar mass to find the mass per dm3.
    Oh i see how silly of me , thanks for your help .
  4. Offline

    ReputationRep:
    (Original post by ch0wm4n)
    Oh i see how silly of me , thanks for your help .
    Is this OCR A? (Looks like it.)
    A lot of people have been talking about '40.'

Reply

Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  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
    your full birthday is required
  1. By joining you agree to our Ts and Cs, privacy policy and site rules

  2. Slide to join now Processing…

Updated: June 10, 2012
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.

Today on TSR

What uni's really like

Chill those freshers fears...

Poll
Would you date a smoker?
Study resources
x

Looking for some help?

Ask our friendly student community a question

Ask a question now

Or get help from our smart tools and guides

GCSE help A-level help Uni application help Everything else
Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.