Forum home Road cycling forum The bottom bracket

OT - chemistry question

mmukmmuk Posts: 398
edited January 2011 in The bottom bracket
help wanted - please!

''how much salicylic acid is needed to make one 300mg aspirin tablet''

molar mass salicylic = 138 1 mole = 2.174
mm aspirin = 180 1 mole = 1.667

any chemists/chemistry students out there?

cheers

Mike

Posts

  • Mike67Mike67 Posts: 585
    If you're making it this way:

    C7H6O3 (Salicylic acid) + C4H6O3 (Ethanoic anhydride) => C9H8O4 (Aspirin) + C2H4O2 (Acetic acid)

    Then it's a 1 to 1 stoichiometry so you would need (2.174/1.667)x0.3g which in my book equates to 0.391g, assuming a perfect reaction.

    Now I've got a headache :wink:
    Mike B

    Cannondale CAAD9
    Kinesis Pro 5 cross bike
    Lots of bits
  • pbt150pbt150 Posts: 338
    Not sure that's right Mike.

    .3 g /180.1 g/mol = 1.667 milli moles of aspirin in the tablet.

    Assume 1:1 reaction that goes to completion.

    1.667 mmoles x 138.1 g/mole = .230 g salicylic acid required.
  • mmukmmuk Posts: 398
    thanks gents - I have been struggling with that all night!

    Mike
  • mmukmmuk Posts: 398
    a third source has come up with:

    Salicylic acid + Ethanoic anhydride = aspirin + acetic acid
    1 mol + 1 mol = 1 mol + 1 mol
    138g + 102g = 180g + 60g

    Therefore, if 138g of salicylic acid are needed to make 180g of aspirin, multiply by 1.6 and divide by 1000 to give you 300mg.

    =230mg


    for anyone who's interested!

    MM
  • beverickbeverick Posts: 3,461
    ZZZZZZZzzzzzzzzzzzzzzzzzzzz
  • Mike67Mike67 Posts: 585
    pbt150 wrote:
    Not sure that's right Mike.

    .3 g /180.1 g/mol = 1.667 milli moles of aspirin in the tablet.

    Assume 1:1 reaction that goes to completion.

    1.667 mmoles x 138.1 g/mole = .230 g salicylic acid required.

    You are correct...read it far too quickly as usual and took the second numbers as the molar masses :oops: Sorry OP.

    It then becomes (138/180)x300mg which does indeed = 0.23g (230mg).

    Back to cycling I think :D
    Mike B

    Cannondale CAAD9
    Kinesis Pro 5 cross bike
    Lots of bits
  • MattC59MattC59 Posts: 5,433
    After thinking back to my A-Level chemistry, I remembered it's Friday and gave up :D
    Science adjusts it’s beliefs based on what’s observed.
    Faith is the denial of observation so that Belief can be preserved
  • Homer JHomer J Posts: 932
    it would be easier to buy them.
Sign In or Register to comment.