How to set up a buffer solution?

Question

Ok, Teach says we have to set up a buffer. We are to calculate one that is ± 1 pH from our target pH. We are selecting the target pH and reaction. We are to describe the reaction, calculate it's pH, find pKa from an outside source, and find a suitable buffer via the Henderson-Hasselbach equation: pH = pKa + log (H/HA).

The hard part? I have no idea what to do or how to start. The prof was really vague as to how we are to set it up, which is why I am confused. I will ask him for details, but if anyone has any experience with this, it would help. Would be nice to have a breakdown of the process for selecting a buffer. Sorry if I asked a vague question. I have only a vague assignment to work with. I will pin him down today and get the exact details.

And please don't quote wiki. I know how to use the google, because I invented the internet.

Answer 1

The important thing with a buffer solution is to realise that it is the ratio between the molarities of the weak acid and its salt that is important, and not the actual amounts present. If the ratio is 1:1, then pH = pKa. For every 10-fold change in this ratio, the pH changes by 1 unit.

There are two ways of preparing a buffer solution.
a) throw in the two separate compounds (eg ethanoic acid and sodium ethanoate) into the same solution
b) take some ethanoic acid, and add approximately half its number of moles of sodium hydroxide. This will turn half of it into sodium ethanoate, leaving half of the ethanoic acid unchanged. I am certain that this is the method that you are supposed to use.

Now you can do the rest!

Answer 2

The molecular reaction is NaCN(aq) + HCN(aq) -----> HCN(aq) + NaCl(aq) HCN is a susceptible acid and least perplexing partly ionizes. the internet ionic reaction is CN-(aq) + H+(aq) ------> HCN(aq) If there is molar far greater than NaCN then the two HCN and NaCN would be in answer; this may well be a blend of a susceptible acid (HCN) and ions of its conjugate base (CN-, from dissociated NaCN), which varieties a buffer. A, b, and c do no longer type any HCN, and d does no longer type any CN- ions. in basic terms e does each and each. in spite of the undeniable fact that e will type a buffer presented that there are greater desirable moles of NaCN than HCl.

Answer 3

first of all,yours is not a vague question.Having said that, to deal with buffer you need to have good understanding of following concepts
1] salt
2] salt hydrolysis
3] weak acid and
4] common ion effect.
I suggest you to go through it first,and then study buffer.