[sophie]

I usually use a pH meter when preparing a buffer.  I've been told that it is better to calculate and measure out the acid/base to adjust pH.  Why? and how to you calculate that?

[crow_of_darkness]

    You can measure ph with the relation of Hederson-Hasselbah: ph=pk+(c of salt/c of sharply)
    k= dissension of sharply, c= concentration.

[Borek]

I usually use a pH meter when preparing a buffer.  I've been told that it is better to calculate and measure out the acid/base to adjust pH.  Why? and how to you calculate that?

If you have standard substances at hand you may try to prepare buffer of known pH with them without using pH meter. Standard substance has high purity and is easy to dry, so that you can weight it and know exact amount used. Calibration buffers are defined this way.

However, usually you are making buffer not with standard substances, but with substances that are convenient to use. Acetic acid for example - it is not a standard subtance, it is usually used as a solution of not very precisely known concentration. Or you may use salt - like sodium acetate - that is pure, but hard to dry, so you never know how much water it contains. Thus it is not easy to prepare buffer measuring amounts of substances not to mention the fact, that it is not easy task to weight exactly 0.8765 g of anything ). Thus for practical purposes it is much more convenient to pepare a buffer and adjust its pH precisely using pH meter.

Sometimes it doesn't matter, as the differences in pH are rarely higher than 0.1-0.2 pH unit (assuming you prepare buffer without any large, systematic error) -and for many applications such precision is enough.

[Borek]

k= dissension of sharply

the only word I understand is "of"  

[crow_of_darkness]

    First of all i want to congratulate Borek for notice that. The truth is that my English are not perfect and i usually use a dictionary for the translation. Well, dictionaries have a big disadvantage. The word i am looking for has many other words in English that means the same thing. The problem is that every word used for different expression . E.g: big=large=gret. BUT you have to say ONLY Alexander the great, NOT Alexander the large.YOU SEE THE PROBLEM HERE?(For a person that doesnt speak excellent the language.)
    So: sharply OR sharp =acid AND dissencion=disagreement=dimension. Now which is the proper word, thats the problem and i am sorry if i create problem but i really want to participate in the forum  

[Borek]

First of all i want to congratulate Borek for notice that. The truth is that my English are not perfect and i usually use a dictionary for the translation.

Don't worry, English is my second language too. What is your first language?

So: sharply OR sharp =acid AND dissencion=disagreement=dimension. Now which is the proper word, thats the problem and i am sorry if i create problem but i really want to participate in the forum  

Funny thing is - if not for the context - I will still don't know what you mean. Luckily I know k in the Henderson-Hasselbalch equation is acid dissociation constant

[crow_of_darkness]

    I am Greek, and K has the meaning that you mentioned.Finaly we found a see