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Offline lha08

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buffer solution
« on: April 19, 2009, 11:14:31 AM »
Determine the pH of 35 mL of distilled water after the following volumes of 0.20 hydrochloric acid solution have been added: 0.0 mL and 5.0 mL
and (separate question) 0.0 mL and 5.0 mL of a 0.20 mol/L sodium hydroxide solution, NaOH.
I need help please because i don't know what to do!
Thanks!

Offline Borek

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Re: buffer solution
« Reply #1 on: April 19, 2009, 03:07:45 PM »
This is not a buffer, it is direct application of dilution and pH definition.
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Offline lha08

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Re: buffer solution
« Reply #2 on: April 19, 2009, 03:15:17 PM »
This is not a buffer, it is direct application of dilution and pH definition.

ohhh okay...so when i tried to solve for the 5.0 mL of the 0.20 mol/L NaOH solution part, i'm not sure if i'm doing it correctly but the initial pH is 4.45 so i converted that pH to find [H] (10^-4.45) and it's the same as [OH] since 1:1 ratio. From there, i found the moles of OH by simply multiplying that number by the total volume (35 mL).
Then i used the 0.20 mol/L NaOH and found the number of moles of OH by multiplying it by 5 mL (the volume of NaOH added).
THen i added both number of moles of OH and divided it by the total volume (40 mL) and found the pH from there...(12.39)..
Is what i'm doing correct?? Thanks..


Offline Borek

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Re: buffer solution
« Reply #3 on: April 19, 2009, 04:13:50 PM »
Where did you get 4.45 from, you have not mentioned it in your first post.

I suppose you have asked the same question earlier on physicsforums? If so, you need to post the question exactly as it is worded. We can help, but we are not able to guess missing data. Even combining information from both sites is not enough to understand what the question really asks about.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline lha08

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Re: buffer solution
« Reply #4 on: April 19, 2009, 05:44:03 PM »
Where did you get 4.45 from, you have not mentioned it in your first post.

I suppose you have asked the same question earlier on physicsforums? If so, you need to post the question exactly as it is worded. We can help, but we are not able to guess missing data. Even combining information from both sites is not enough to understand what the question really asks about.

Well i had to worded myself because it's from an experiment that i did in class and i just have to fill in the blanks...but the 4.45 is the initial pH buffer.

Offline Borek

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Re: buffer solution
« Reply #5 on: April 19, 2009, 06:41:17 PM »
You have to know buffer type and concentration. Otherwise it is a no go.
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