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Topic: % ionization,pH, concentration  (Read 8230 times)

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moni

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% ionization,pH, concentration
« on: April 10, 2006, 12:27:21 PM »
a) the ionization constant Ka of formic acid ,HCO2H is 1.80 *10^-4. What is the percent ionization of a 0.00100 M solution of this acid?

b)The  pH of a 0.072 M solution of benzoic acid HC7H5O2 is 2.86.compute  Ka for this acid?

c)What concentration of acetic acid HCH3CO2 is needed to give a [H+]=3.5 *10^-4? Ka = 1.75 *10^-5

For the a) i'm not sure  but :

HCO2H ----> HCO2-  + H+

% ionization =HCO2H/H+  *100%

Ka = [HCO2-][H+]/[HCO2H]
1.8*10^-4 = (x)(x)/0.417M
x^2=(1.8*10^-4)(0.417)
x=8.6*10^-3

% ionization= 1.80*10 ^-4/8.6*10^-3 *100%
% ionization = 2.09%

am i on the right truck?

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Re: % ionization,pH, concentration
« Reply #1 on: April 10, 2006, 12:41:09 PM »
1.8*10^-4 = (x)(x)/0.417M

What is 0.417?

Regardles of where did you get this number from - the equation is wrong. Numerator depends on x.

Quote
am i on the right truck?

Depends on where you are going :)
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moni

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Re: % ionization,pH, concentration
« Reply #2 on: April 10, 2006, 02:08:41 PM »
Numerator depends on x.

what does it mean?

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Re: % ionization,pH, concentration
« Reply #3 on: April 10, 2006, 02:17:43 PM »
Sorry - I meant denominator is a function of x (numerator is function of x too, but that is already visible in your formula).
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moni

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Re: % ionization,pH, concentration
« Reply #4 on: April 10, 2006, 02:52:32 PM »
but like u said the equation is wrong,that means  everything is wrong

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moni

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Re: % ionization,pH, concentration
« Reply #6 on: April 10, 2006, 04:23:20 PM »
HCO2H + H2O----> HCO2- + H3O  is it right? 

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Re: % ionization,pH, concentration
« Reply #7 on: April 10, 2006, 04:25:53 PM »
Yes, but you may safely omit water for these calculations, and assume it is H+, not H3O+. There is less writing when solving ;)
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moni

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Re: % ionization,pH, concentration
« Reply #8 on: April 10, 2006, 04:32:55 PM »
HCO2H ----> HCO2-  + H+ so that is good too

Ka is wrong, but from  Ka = [H][A] /[HA]

Ka = [HCO2-][H+] / [HCO2H]

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Re: % ionization,pH, concentration
« Reply #9 on: April 10, 2006, 04:46:05 PM »
So far so good.
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moni

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Re: % ionization,pH, concentration
« Reply #10 on: April 10, 2006, 05:17:20 PM »
1.8 *10^-4 =(x)(x) /x-0.0100

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Re: % ionization,pH, concentration
« Reply #11 on: April 10, 2006, 05:27:25 PM »
0.01 or 0.001?

And x-0.01 or 0.01-x?
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moni

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Re: % ionization,pH, concentration
« Reply #12 on: April 10, 2006, 08:43:59 PM »
0.01-x

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Re: % ionization,pH, concentration
« Reply #13 on: April 11, 2006, 02:24:36 AM »
So far so good. What next?
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