Posted by **Anonymous** on Thursday, November 4, 2010 at 10:32am.

Calculate the pH of a 0.5 M Formic Acid (HCOOH) soln. ka= 0.00018

- College Chemistry -
**bobpursley**, Thursday, November 4, 2010 at 10:52am
Ka=[H][COOH]/([HCOOH]

ka= x^2/(.5-x)

solve this for x

x^2+.00018x-.5*.00018=0

x=(-.00018+-sqrt(.00018^2+.00036))/2

x=-.00009+- .00948= .00939 check all that math.

pH=-log (.00939)=2.03

check the math.

- College Chemistry -
**Dr Russ**, Thursday, November 4, 2010 at 10:52am
The equilibrium is given by

HCOOH -> H+ + HCOO-

so Ka=[H+][HCOO-]/[HCOOH]

if we start with 0.5M HCOOH then at equilibrium there is [H+] = x and [HCOO-]=x and HCOOH=0.5-x

so Ka = (x)(x)/(0.5-x)=0.00018

this gives a quadratic to solve, however, we only want the answer to 1 sig fig (.5M is 1 sig fig) so we can say that 0.5-x is approximately equal to 0.5, because x will be small.

thus x^2/0.5=0.00018

hence you can find x

pH is then -log(x)

which is pH=2, but check the maths.

## Answer This Question

## Related Questions

- chemistry - What mass of solid sodium formate (of MW 68.01) must be added to 115...
- ap chemistry - What mass of solid sodium formate (of MW 68.01)must be added to ...
- Chemistry - Calculate the pH of solution made by combining 75.0 mL of 0.10 M ...
- CHEM - Calculate the pH of solution made by combining 75.0 mL of 0.10 M formic ...
- AP Chemistry - A buffer solution contains .4mol of formic acid, HCOOH and a ....
- Chemistry - A 50.0 mL sample of 0.12 M formic acid, HCOOH, a weak monoprotic ...
- Chemistry - How many grams of formic acid, HCOOH, must be added to 0.270L of 0....
- Chemistry - Calculate the pH, to one decimal place, of the solution made by ...
- Chemistry - Find the pH of mixture of acids. 0.185 M in HCHO2 and 0.225 M in ...
- Chemistry pH - What is the pH of a solution that is .60 M H2SO4 (Sulfuric acid) ...

More Related Questions