posted by Vanessa on .
Wilh this form a buffer?
50 mL of .10 M HCl; 35 mL of .150 M NaOH
Moles of HCl= .005
Moles of NaOH= .00525
total litres of solution= .05 + .035= .085 L
[HCl]= .005 mol/.085 L = .0588 M
[NaOH]= .00525 mol/ .085 L = .0618 M
Ka of HCl= 1.3*10^6
pKa= -log(1.3*10^6) = -6.114
Plug into H-H equation...
pH= pKa + log [A-]/[HA]
pH= (-6.114)+ log (.0618/.0588)
I am stuck.. I don't think this value is supposed to be negative. How does the pH of the solution tell someone whether or not the soltion is a buffer?
Generally, calculating the pH will not tell you if the solution is a buffer or not although it may give some hints. Your best bet is to know the definition of how to prepare a buffer.
A weak acid and its salt or a weak base and its salt (or solutions that will make those) will be a buffered solution.
Therefore, acetic acid and some salt such as sodium acetate or potassium acetate will be a buffer. Alternatively, one can add NaOH to acetic acid (which makes the salt, sodium acetate) but not add enough NaOH to neutralize all of the acetic acid. That means you will have some acetic acid (a weak acid) left over and the sodium acetate the reaction provided gives the weak acid and its salt and that is a buffered solution.
A basic buffer might be NH4Cl and NH3(aq) OR NH3 plus some HCl (but not enough to neutralize all of the NH3).
So what about this solution you have? Is HCl a strong acid or a weak acid? Is NaOH a strong base or a weak base? If you don't know, look up the Ka value and Kb value in tables in your text. They will not be listed in those tables MEANING that they are a strong acid and a strong base. And that isn't the recipe for a buffer.
i don't no