Wednesday

September 3, 2014

September 3, 2014

Posted by **Kati** on Friday, February 6, 2009 at 4:25pm.

How does one approach this question?

Kati

- Chemistry, help. -
**DrBob222**, Friday, February 6, 2009 at 4:43pmNaOCl = 5.25% which means 5.25 g NaOCl + 94.75 g of water but since the density of the solution is 1.00 g/mL then that's 94.75 mL water.

moles NaOCl = 5.25 g NaOCl/molar mass NaOCl = 5.25/74.44 = 0.0705 moles NaOCl.

That is in 94.75 mL H2O or 0.09475 L so molarity is 0.0705/09475 = 0.744 M. check my arithmetic.

OCl^- + HOH ==> HOCl + OH^-

Kb = Kw/Ka = (HOCl)(OH^-)/(OCl^-)

Look up Ka for HOCl. Kw = 1 x 10^-14. In the equation you know (HOCl)=(OH^-) so solve for (OH^-), convert that to pOH, and convert that to pH.

Post your work if you get stuck.

- Chemistry, help. -
**Kati**, Friday, February 6, 2009 at 5:06pmOk, so I found the Ka and then found the Kb. I got 2.857x10^-7. I then subbed that into the equation: [x^2]/[0.744-x]...you can use the assumption rule to get rid of the minus x in the denominator. When I solved I got x=0.0000461043, and a pH of 3.34. What went wrong? The answer is supposed to be 10.7 which makes sense, since the products are basic.

Thanks

Kati

- I FIGURED IT OUT! :) -
**Kati**, Friday, February 6, 2009 at 5:29pmI understand what I did! The 3.34 is the pOH thus, 14-pOH is the pH which is 10.66 or 10.7 :)

Thanks very much!!

-Kati

- Chemistry, help. -
**DrBob222**, Friday, February 6, 2009 at 5:30pmNothing went wrong except that you forgot to think about your answer. IF you look at the equation, what did you let X stand for? The answer is that you let it stand for (OH^-). So you found the pOH (when you took the negative log) thinking that was the negative log of H^+. Just subtract that from 14 to get pH. 14 -3.3 = 10.7. Voila! Ain't chemistry interesting? Besides that, it keeps one on one's toes.

**Answer this Question**

**Related Questions**

Chemistry - A solution of household bleach contains 5.25% sodium hypochlorite, ...

chemistry - A solution of household bleach contains 5.25% sodium hypochlorite, ...

Chemistry - A solution of household bleach contains 5.25% sodium hypochlorite, ...

Chemistry Help Please - Titration of a Sample of Household bleaches: The ...

CHEMISTRY - A solution household bleach contains 5.25% NaClO, by mass. Assuming ...

chemistry........help!! =) - One brand of laundry bleach is an aqueous solution ...

GK..please check...Chemistry Help Please - Moles of S203^2- = (molarity)(volume...

Chemistry - A solution household bleach contains 5.25% NaClO, by mass. Assuming ...

Chemistry - Calculate [ClO^-] in a 6% bleach solution. A 6% bleach solution ...

Chemistry - Calculate [ClO^-] in a 6% bleach solution. A 6% bleach solution ...