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Preparing buffers for pH testing


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#1 Gamewizard

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Posted 23 July 2015 - 07:56 AM

Hi,

 

I need to prepare some buffers, namely HCl and NaOH. I  want to prepare them at concentrations higher than 0.1M. The NaOH i have is just in pellet form and does not have a concentration or anything.  The HCl is in liquid form and is 0.1 M.   My question is can i use this 0.1M HCl to make    0.3 M HCl ?  i need about 1 litre. And also the NaOH, how much will i have to add to make 0.3 M solution (1 litre)?

 

Please help



#2 hobglobin

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Posted 23 July 2015 - 10:06 AM

grams NaOH:

m = M * c * V

mass (g) = molar mass (39.99 g/mole) * concentration (0.3 moles/L) * volume (1 L)

 

m= 11.99 grams (or better 12 g because the NaOH pellets are quite hygroscopic and it won't be that exact anyway (and be not too slow with weighing).

 

You cannot make an "undilution",i.e. you cannot concentrate a solution out of a more diluted one (except you invest in equipment and efforts which is compared to getting a more concentrated solution, useless, and with HCl almost impossible).

 

And finally, for me these are an acid and a base and not buffers.



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#3 Gamewizard

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Posted 24 July 2015 - 01:47 AM

grams NaOH:

m = M * c * V

mass (g) = molar mass (39.99 g/mole) * concentration (0.3 moles/L) * volume (1 L)

 

m= 11.99 grams (or better 12 g because the NaOH pellets are quite hygroscopic and it won't be that exact anyway (and be not too slow with weighing).

 

You cannot make an "undilution",i.e. you cannot concentrate a solution out of a more diluted one (except you invest in equipment and efforts which is compared to getting a more concentrated solution, useless, and with HCl almost impossible).

 

And finally, for me these are an acid and a base and not buffers.

 

Thank you for explaining that formula so well.  I am just worried about the HCl now,  this means I would have to obtain a a 0.3 M HCl solution then.






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