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If acetic acid is the only acid that vinegar contains [Ka = 1.8*10-5] , calculate the concentration of acetic acid in the vinegar.

pH of vinegar is 3.20

First I got the antilog of the pH given, which turned out to be 6.309E-4.
Then I did [(6.309E-4)^(2)]/(1.8E-5)to get .022113, but when I typed in that answer I was told to check my calculations because I might be missing a 'term.' I have no idea what to do after this point.

  • Chemistry -

    The concentration should be in molarity M. and it looks like you put in too many significant figures in the answer part. 0.022 M is what I would have put in.

  • Chemistry -

    Yeah that is what I put in as my answer since it asked for two sigfis, but it was still wrong.

  • Chemistry -

    HAc+ H2O---> Ac + H3O+

    10^(-3.10)=6.310 x 10^-4 M

    Ka=[6.310 x 10^-4 M][6.310 x 10^-4 M]/x

    Ka=1.8 x10^-5=[6.310 x 10^-4 M][6.310 x 10^-4 M]/x

    3.982 x 10^-7/1.8 x10^-5=[x]

    x= 0.022 M

    Not sure what to tell you.

  • Chemistry -

    Unless they wanted 3 sig figs, which would be 0.0221M.

  • Chemistry -

    I got the same answer and had the same problem but it worked when I put in .0221... it says the right answer is 2.3×10−2

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