# Chemical Forums

• February 19, 2017, 10:03:42 AM
• Welcome, Guest

•

•

### Chemistry Books

Pages: [1]   Go Down

### AuthorTopic: Find the pH of a 0.000100 M solution of HOBr?  (Read 5223 times) !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="https://platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() {var po = document.createElement("script"); po.type = "text/javascript"; po.async = true;po.src = "https://apis.google.com/js/plusone.js";var s = document.getElementsByTagName("script")[0]; s.parentNode.insertBefore(po, s);})();

0 Members and 1 Guest are viewing this topic.

#### merced

• Guest
##### Find the pH of a 0.000100 M solution of HOBr?
« on: April 25, 2006, 05:48:12 PM »

Find the pH of a 0.000100 M solution of HOBr.

Given: Ka = 2.0 * 10-9

Using a RICE table, Ka = [OBr-][H3O+] / [HOBr]

Let [OBr-] = [H3O+] = x

I got the 2nd degree polynomial: 0 = x2 + 2.0 * 10-9 x - 2.0 * 10-13
Solving for x, I get: x = 4.462 * 10-7 = [H3O+]

Then I find that the pH = 6.350.

The answer supposedly has a pH of 6.262.  What did I do wrong?
« Last Edit: April 30, 2006, 02:23:48 PM by Mitch »
Logged

#### AWK

• Global Moderator
• Sr. Member
• Mole Snacks: +438/-77
• Online
• Gender:
• Posts: 6108
##### Re: find the pH of...
« Reply #1 on: April 25, 2006, 08:34:19 PM »

Try to include an auto-dissociation of water to your calculations. This leads to a cubic equation.
Logged
AWK

#### Borek

• Mr. pH
• Deity Member
• Mole Snacks: +1532/-389
• Online
• Gender:
• Posts: 23312
• I am known to be occasionally wrong.
##### Re: find the pH of...
« Reply #2 on: April 25, 2006, 09:35:07 PM »

Then I find that the pH = 6.350.

The answer supposedly has a pH of 6.262.  What did I do wrong?

Your result is correct. BATE gives pH=6.34 and calculation result includes all possible equilibria present in the solution.

Check it by yourself - link to BATE is in my signature, you will have to enter pKa (8.69) manually, as hypobromous acid is not present in the default (demo version) database.
Logged
Chembuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### merced

• Guest
##### Re: find the pH of...
« Reply #3 on: April 27, 2006, 03:44:09 PM »

thanks!
Logged

#### celestial_kasumi

• Guest
##### Re: find the pH of...
« Reply #4 on: April 30, 2006, 03:31:34 AM »

can i add to this question list?

50ml of HCl 0.0100M added to 50ml 0.0100M NaOH, what is the pH?
thnx
Logged

#### Alberto_Kravina

• Assault Chemist
• Retired Staff
• Full Member
• Mole Snacks: +70/-15
• Offline
• Posts: 607
##### Re: find the pH of...
« Reply #5 on: April 30, 2006, 03:34:15 AM »

Easy. Calculate how much NaCl forms (NaCl is a neutral salt since it is a salt of a strong acid and a strong base). Then you can see if there's an excess NaOH or HCl. Then you can simply calculate the pH with the formula pH= - lg(c0) since NaOH and HCl are both strong a strong base and a stong acid.
But think a bit before caculating and wasting your time...the same volume of a monoprotic base with the same concentration of the acid is added to a monoprotic acid...what could happen ?
« Last Edit: April 30, 2006, 03:36:38 AM by Alberto_Kravina »
Logged

#### Borek

• Mr. pH
• Deity Member
• Mole Snacks: +1532/-389
• Online
• Gender:
• Posts: 23312
• I am known to be occasionally wrong.
##### Re: find the pH of...
« Reply #6 on: April 30, 2006, 04:19:40 AM »
Logged
Chembuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info
Pages: [1]   Go Up

Mitch Andre Garcia's Chemical Forums 2003-Present.

Page created in 0.081 seconds with 23 queries.