chemistry
posted by Sarah .
Lactic acid, HC3H5O3(aq) is a weak acid that gives yougurt its sour taste(Yeeeeecccckkk). Calculate the pH of a 0.0010 mol/L solution of Lactic acid. The Ka for lactic acid is 1.4 x 10^4
For Further Reading
chemistry  DrBob222, Saturday, April 5, 2008 at 7:39pm
Let's call Lactic acid HL.
HL ==> H^+ + L^
Ka = (H^+)(L^)/(HL) = 1.4 x 10^4
initially before ionization:
(HL) = 0.001 M
(H^+) = 0
(L^) = 0
change:
(H^+) = +x
)L^) = +x
(HL) = 0.001  x
equilibrium:
(H^+) = +x
(L^) = +x
(HL) = 0.001  x
Substitute the equilibrium values shown into the Ka expression and solve for x.
Then convert (H^+) to pH by pH = log(H^+)
Here is my work
Ka = H^+)(L^)/(HL) = 1.4 x 10^4
=(+x)(+x)/(0.001  x ) = 1.4 x 10^4
= (x^2) / (0.001  x) = 1.4 x 10^4
What is my next step sorry:)

You have two choices.
1)The simple choice, and one which doesn't always work, is to assume x is very small in comparison with 0.001 so that 0.001  x = 0.001. That way you don't have a quadratic equation. You can try that, then see if 0.001  x = about 0.001 or not. If x is too large, that won't work.
#2 choice. Solve the quadratic.
x^2 = 1.4 x 10^4 x (0.001  x) and go from there. Many caculators now have a quadratic solver built in (or they can be programmed to solve a quadratic).
#3 choice. Technically, this isn't another choice. But sometimes the quadratic can be solved by successive approximations which may or may not be easier than solving the quadratic by brute force. I don't know if this one will work that way or not.
I'll leave you with those choices and you let me know which ones you need help with. (and why?)
Respond to this Question
Similar Questions

chemistry
Lactic acid, HC3H5O3(aq) is a weak acid that gives yougurt its sour taste(Yeeeeecccckkk). Calculate the pH of a 0.0010 mol/L solution of Lactic acid. The Ka for lactic acid is 1.4 x 10^4 
Dr Bob
What is the pH of the solution that results from mixing 5 ml of 0.2 M NaOH and 100 mL of 0.05 M lactic acid? 
Chemistry
An 0.0284 aqueous solution of lactic acid is found to be 6.7% ionized. Determine Ka for lactic acid. HC3H5O3 + H2O < > H3O^+ + C3H5O3^ Ka =? 
Chmeistry
A lactic acid/lactate ion buffer solution contains 0.19 M HC3H5O3 and 0.78 M C3H5O3, respectively. The Ka value of lactic acid is 1.4*10^4. Calculate the pH of this buffer. 
Chemistry
A lactic acid/lactate ion buffer solution contains 0.19 M HC3H5O3 and 0.78 M C3H5O3, respectively. The Ka value of lactic acid is 1.4*10^4. Calculate the pH of this buffer. 
chemistry
Lactic acid, C3H6O3, is found in sour milk. A solution containing 1.00g NaC3H5O3 in 100.0mL of 0.0500M C3H6O3 has a pH= 4.11. Calculate the Ka of lactic acid 
Chemistry
Lactic acid, C3H6O3. If the initial concentration of lactic acid is 0.12 mol/L and the pH is 2.39, what is the Ka for lactic acid? 
chemistry
Lactic acid is a weak monoprotic acid. If a 0.10 M solution of it has a pH of 2.44, what is the dissociation constant (Ka) for lactic acid. I got 1.3x10^4? 
chemistry
Lactic acid, CH 3 CHOHCO 2 H, is found in sour milk, in sauerkraut, and in muscles after activity. K a for lactic acid = 1.4 x 10 4 . a. If 2.75 g of NaCH 3 CHOHCO 2 , sodium lactate, is added to 5.00 x 10 2 mL of 0.100 M lactic acid, … 
chemistry
A lactic acid/lactate ion buffer solution contains 0.43M HC3H5O3 and 0.90M C3H5O3. The value of lactic acid is 1.4*104 calculate the pH of this buffer