Monday

March 30, 2015

March 30, 2015

Posted by **jessica** on Tuesday, November 23, 2010 at 2:38pm.

i got help with this problem, but i dont get where one of the numbers came from (3.4 x 10^-5)??? i tried makeing 3.0 x 10^-8 the x but i still dont get that number.

start

0.0385

change

-x. . . . .. . +x. . . .+x

at equilibrium

0.0385-x. .. x..... . .x

Ka = 3.0 x 10^-8 = [H+][ClO-]/ [HClO]= (x)(x)/ 0.0385-x

x = [H+]= 3.4 x 10^-5 M

pH = - log 3.4 x 10^-5=4.5

- chemistry -
**J**, Tuesday, November 23, 2010 at 3:17pmHiya,

From what you said it seems that you understand everything up till "x = [H+]= 3.4 x 10^-5 M"

So we know that 3X10^-8 = x^2/(0.0385-x)

Bring (0.0385-x) over to the left hand side,

Hence 3X10^-8(0.0385-x) = x^2

Then we expand the left hand side,

1.155X10^-9 - 3X10^-8x = x^2

From there we bring all terms to the right hand side to give

x^2 + 3X10^-8x - 1.155X10^-9 = 0

Then we use our quadratic formula to solve for x --> x = [-b +/- sqrt(b^2-4ac)]/2a and reject the negative answer since x = concentration of H+ which cannot be negative. Then we get 3.4X10^-5 M.

Alternatively, if the math is a little too tedious, we can approximate x to be near zero since HClO is a weak acid which only dissociates very little in aqueous solution. Then we get 3X10^-8 = x^2/0.0385 which should be slightly simpler to solve.

Hope I helped!

- chemistry -
**jessica**, Tuesday, November 23, 2010 at 3:26pmwhere is 1.155X10^-9 from?

- chemistry -
**J**, Wednesday, November 24, 2010 at 7:43amThat comes from multiplying 3X10^-8 and 0.0385 when we expand 3X10^-8(0.0385-x).

**Answer this Question**

**Related Questions**

Biochemistry - Explain how to prepare 1L of a buffer at pH 7.4 using 1M ...

Biochemistry - Explain how to prepare 1L of a buffer at pH 7.4 using 1M ...

chemistry - Ka for hypochlorous acid, HClO, is 3.0*10^(-8). Calculate the pH ...

Chemistry - A student was required to prepare 250.0 mL of a hypochlorous acid/...

bio chem - Explain how to prepare 1L of a buffer at pH 7.4 using 1M hypochlorous...

Chemistry - the ka of hypochlorous acid hclo is 3.5 x 10^-8. What is Kb for the ...

152 - Ka for hypochlorous acid,HCLO, IS 3.0*10^-8. Calculate the pH after 10.0,...

Organic Chemistry - How many moles of hypochlorous acid are needed to react with...

Chemistry - Can the 5% approximation be used to determine the pH of the ...

last proofreading for the weekend - name an acid when given the formula of acid ...