Making pH buffers

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MariaC
Posts: 174
Joined: 29 Oct 2008, 12:34
School: Central Coast Grammar School
Suburb: Erina Heights
State/Location: NSW

Making pH buffers

Post by MariaC »

#-o Im very!!!!!new at this, I have to make up some pH buffers to calibrate our pH probe, I purchased buffer capsules of pH 4 and 7, the instructiions to make up specify CO2 free water, is my distilled water good enough??? the chem teacher claims its pH is too low but not sure how he confirmed this when the pH probe has never been calibrated!!!! Any feedback would be appreciated. Great site by the way! :D
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lada
Posts: 1024
Joined: 29 Jun 2006, 10:00
State/Location: NSW

Re: Making pH buffers

Post by lada »

Hi maria, and welcome. \:D/
Yes, distilled water is perfect for making pH solutions from tablets. Just make sure you do dilution according to instructions. I use them all the time and they are pretty accurate/
Also to make pH 4 you can use

50mL 0.1M potassium hydrogen phthalate (20.4g / L)
plus 0.4mL 0.1 sodium hydroxide
and make up to 100 mL with distilled water. This should be accurate.

But honestly, I would stick with the capsules.
Lada :coffee:
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lada
Posts: 1024
Joined: 29 Jun 2006, 10:00
State/Location: NSW

Re: Making pH buffers

Post by lada »

Sorry Maria,
the sodium hydroxide is also 0.1 M
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