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    okay so i have these two questions for my chem hwk and i just want to check with someone that ive worked it out correctly
    calculate the ph of the following buffer solution:
    12.2g of benzoic acid and 7.20g of sodium benzoate in a 250cm3 aqueous solution
    Ka for benzoic acid is (6.30x10^-5)

    so firstly i worked out the moles of each of them and got:
    benzoic acid = 0.1 moles
    sodium benzoate = 0.05 moles

    from that i then calculated concentrations getting:
    benzoic acid= 0.4
    sodium benzoate = 0.2

    i then plugged this into the equation of [H+] = Ka x [products]/[reactants]
    and got an answer of pH 4.5 ((after doin the -log thing)

    is this correct???
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    (Original post by ilovethe1975)
    okay so i have these two questions for my chem hwk and i just want to check with someone that ive worked it out correctly
    calculate the ph of the following buffer solution:
    12.2g of benzoic acid and 7.20g of sodium benzoate in a 250cm3 aqueous solution
    Ka for benzoic acid is (6.30x10^-5)

    so firstly i worked out the moles of each of them and got:
    benzoic acid = 0.1 moles
    sodium benzoate = 0.05 moles

    from that i then calculated concentrations getting:
    benzoic acid= 0.4
    sodium benzoate = 0.2

    i then plugged this into the equation of [H+] = Ka x [products]/[reactants]
    and got an answer of pH 4.5 ((after doin the -log thing)

    is this correct???
    Working out the concentrations is an unnecessary step as the volume is the same for all components.

    ka = [H+] x mol salt/mol acid

    6.3 x 10-5 x 2 = [H+]

    [H+] = 1.26 x 10-4

    pH = 3.90
 
 
 
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