Buffer Solutions

General Chemistry II lecture covering buffer solutions of acids and their conjugate bases. Buffer solutions are designed to maintain the pH of solution by reacting with small amounts of added acid or base. We show how to calculate the pH of a buffer solution using the Henderson-Hasselbalch equation, and how to select an appropriate acid-base combination to prepare a buffer solution at any desired pH.

Category:

Education

Tags:

• General Chemistry
• acid
• base
• buffer solution
• pH
• equilibrium
• Henderson-Hasselbalch

[FWGSD]

is a mixture of ammonia and ammonium chloride considered a buffer solution?

[chemdog8]

@FWGSD Yes, exactly. These form a conjugate acid-base pair, so a solution of both will be a buffer solution. If the concentrations are the same, then the pH of the buffer is equal to the pKa of the acid. In this case, pKa(NH4Cl) = 9.25 so this buffer is basic, with a pH of 9.25.

[Wrinkle5K]

Hello. My question to You is:

Let's say we have H2CO3 or H2SO4. Two ionization constants are given. They ask to calculate the pH. So, what constant should I use? Or should I use both of them and then sum two pH into one? It would be appreciated if You helped me out.

[chemdog8]

For any diprotic acid, the first ionization dominates and you can usually ignore the second ionization. For sulfuric acid, Ka1 is very large (strong acid) so the pH is determined approximately from the bulk acid: 0.2 M H2SO4 makes 0.2 M H+, so pH = -log(0.2)=0.67 and the second ionization contributes nothing. For H2CO3, Ka1 = 2.5E-4 (weak acid) so a 0.2M solution of carbonic acid gives [H+] = 0.00707 M or pH=2.15. The second ionization is MUCH weaker, so contributes almost nothing.

[sedmercado]

can i ask why for instance a strong acid and its salt cannot act as buffer solutions?

[chemdog8]

Sure! Suppose you have HCl (strong acid) and its salt, NaCl (chloride ion is an extremely weak base). The Cl- cannot compete for the H+ ions, so they remain in solution as H3O+ (strong acid). In terms of the math, the pH or solution is approximately equal to the pKa of the acid. If you have a strong acid like HCl, the Ka is about ~100, so the pKa is about 10^(-100) or nearly zero. That means you'll have a strongly acidic solution that essentailly cannot be buffered. OK?

[diamondboy9]

@verma352 Try visitring some grammar and english language videos as well.

[xLivexxLaughx]

chuck wight alriteeeeee

[verma352]

itz gud i learn so much frm here

[yuukayuuto]

You are so good in explaining this! i understood this immediately! :)) may i request if you can make a slide version in PDF type or Power point for us to download ? :D it really helps since my textbook and lecture note is really hard to understand about this Buffer .

[Escadoo11]

This helped sooo much! Thank you! :)

[FWGSD]

@chemdog8 Thanks for the help.

[armalik17]

what does a conjugate acid/base actually mean?

[eSuMatix]

I think I will shoot myself in head!

WTF is he talking about?oO

Tell me how to cook amphetamines!!!