Hey there! Sign in to join this conversationNew here? Join for free

Help with simple equation Watch

Announcements
    • Thread Starter
    Offline

    0
    ReputationRep:
    ......
    • Thread Starter
    Offline

    0
    ReputationRep:
    Im wondering if someone can help me here. I hate these kind of questions...Just not good at them.

    I have 80mL of H2SO4 98%w/w and I need O.1M in 80 mL.

    So far I have worked out that C1V1 = V2C2 is required.

    First of all I worked out the density m/V which equals 1.22 g/,L (Or does it, or do I even need it).

    98% = 98g in 100g solution. Moles = mass/mr = 98/98.079 = 1M

    Am I on the right track...Please help ??
    • Community Assistant
    • Study Helper
    Offline

    14
    ReputationRep:
    (Original post by lucozade99)
    Im wondering if someone can help me here. I hate these kind of questions...Just not good at them.

    I have 80mL of H2SO4 98%w/w and I need O.1M in 80 mL.

    So far I have worked out that C1V1 = V2C2 is required.

    First of all I worked out the density m/V which equals 1.22 g/,L (Or does it, or do I even need it).

    98% = 98g in 100g solution. Moles = mass/mr = 98/98.079 = 1M

    Am I on the right track...Please help ??
    Calculate how many moles of acid there are in the original liquid.

    Now calculate how many moles there would be in 80 ml of 0.1 mol dm-3 solution ...

    Can you see where to go from here?
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by charco)
    Calculate how many moles of acid there are in the original liquid.

    Now calculate how many moles there would be in 80 ml of 0.1 mol dm-3 solution ...

    Can you see where to go from here?
    Am I right or wrong so far?

    Do you mean work out the moles with the formula moles = mass/mr then multiply it by 0.08?

    I am laughably bad at these
    • Community Assistant
    • Study Helper
    Offline

    14
    ReputationRep:
    (Original post by lucozade99)
    Am I right or wrong so far?

    Do you mean work out the moles with the formula moles = mass/mr then multiply it by 0.08?

    I am laughably bad at these
    Your target is a solution with volume 80 ml and a concentration of 0.1 mol dm-3

    This contains 0.08 x 0.1 = 0.008 mol of solute.

    Your original solution is given in w/w (is this correct, not w/v) ?

    If it's w/w then every 100g contains 98g sulfuric acid and 2 grams of water. Without the density of the mixture you cannot find the mass.

    How did you work out the density?
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by charco)
    Your target is a solution with volume 80 ml and a concentration of 0.1 mol dm-3

    This contains 0.08 x 0.1 = 0.008 mol of solute.

    Your original solution is given in w/w (is this correct, not w/v) ?

    If it's w/w then every 100g contains 98g sulfuric acid and 2 grams of water. Without the density of the mixture you cannot find the mass.

    How did you work out the density?
    P=m/v

    The question was definitely written as w/w. But I'm starting to think he's wrong and w/v makes more sense
    • Community Assistant
    • Study Helper
    Offline

    14
    ReputationRep:
    (Original post by lucozade99)
    P=m/v

    The question was definitely written as w/w. But I'm starting to think he's wrong and w/v makes more sense
    How can you use p = m/V if you don't know 'm'?
    • Thread Starter
    Offline

    0
    ReputationRep:
    OH Ffs.

    I used mr mass.

    I truly am an idiot. I hate dilutions
    • Thread Starter
    Offline

    0
    ReputationRep:
    Do I have to determine m first by doing mr mr x moles? H2SO4 mr x .0008?
    • Community Assistant
    • Study Helper
    Offline

    14
    ReputationRep:
    (Original post by lucozade99)
    Do I have to determine m first by doing mr mr x moles? H2SO4 mr x .0008?
    I don't think that you can do the question with w/w values ...

    ... you don't know the mass of the 80ml of stock solution and there is no way to find it without the density.
    • Thread Starter
    Offline

    0
    ReputationRep:
    I googled the density and it is1.8 shall I use that ?
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by charco)
    I don't think that you can do the question with w/w values ...

    ... you don't know the mass of the 80ml of stock solution and there is no way to find it without the density.
    You think I should do it w/v?
    • Community Assistant
    • Study Helper
    Offline

    14
    ReputationRep:
    (Original post by lucozade99)
    You think I should do it w/v?
    Your shout.

    Talk to your teacher about it ...
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by charco)
    Your shout.

    Talk to your teacher about it ...
    Say it is w/w...And I googled the density is this it?

    Would this be it?

    So if in water... in water. In 100g, I have 98g of H2SO4.

    H2SO4 has MM~98g/mol, so thats about 1mol/100g. Density of water is about 1g/mL, and at room temperature, H2SO4 is a liquid with density 1.84g/mL.

    So 98/1.84+2/1=55.3mL, so you I have a liquid with concentration 1mol/55.3mL. The rest is just a dilution to 80mls?
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Should Spain allow Catalonia to declare independence?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.