Describe how to prepare a buffer solution from NaH2 PO4 and Na2 HPO4 to have a pH of 7.5 .

Name: Problem 21, Chapter 17: Chemistry & Chemical Reactivity
Uploaded: 2020-07-06T17:42:31-08:00
Duration: 5 min 27 s
Channel: Connor Siggins
Description: Describe how to prepare a buffer solution from NaH2 PO4 and Na2 HPO4 to have a pH of 7.5 .

Describe how to prepare a buffer solution from NaH2 PO4 and...

Key Concepts

Phosphate Buffer System

The phosphate buffer system, which utilizes salts derived from phosphoric acid, involves multiple dissociation steps due to its polyprotic nature. This system is especially useful near physiological pH values. By adjusting the proportions of the different phosphate species, one can achieve a buffer with a specific pH, an application of the above concepts in a practical setting.

Buffer Solutions

A buffer solution is a mixture that resists changes in pH upon addition of small amounts of acid or base. It typically consists of a weak acid and its conjugate base, or a weak base and its conjugate acid. In preparing a buffer, the right ratio of these components ensures that the solution maintains a nearly constant pH despite external disturbances.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a mathematical formula that relates the pH of a buffer solution to the pKa of the weak acid and the ratio of the concentrations of the conjugate base to the weak acid. This equation is critical in calculating the precise amounts of each component required to achieve the desired pH.

Acid-Base Equilibrium

Acid-base equilibrium involves the balance between a weak acid and its conjugate base in solution. Understanding this equilibrium is essential when preparing buffers because it determines how the components interact and maintain stability in pH. The equilibrium constant (Ka) of the weak acid is used in the Henderson-Hasselbalch equation to relate the ratio of the components to the pH.

Transcript

00:01 Okay, so this question is asking us to create a buffer solution with a ph of 7 .5 using nah2po4 and na2hpo4.

00:14 So nah2po4 is going to be our acid and na2hpo4 is going to be a base.

00:23 And what we're going to do to solve this problem is we're going to use this general equation for buffer solutions.

00:31 So we know that we need the ph of the solution to be 7 .5.

00:37 And that is going to tell us what our hydronium ion concentration is going to be.

00:43 So what we're going to do is we're going to do 10 to the negative 7 .5 is going to be our hydronium ion concentration.

00:55 And that's just a reverse.

00:57 So the ph is the negative log of the hydronium ion concentration.

01:03 So we're just doing that in reverse to get from ph to hydronium ion concentration.

01:08 And then for our k -a, it's going to be, to figure out the k -a, what we can do is we can look at the acid phosphoric acid, which is h -3 -h -3 -p -o -4.

01:26 And this is what's called a tri -protic acid.

01:31 You can see tri means three in latin.

01:34 So we have three protons that this acid can donate.

01:38 And if we look at the acid and base that we're working with in this problem, which i will circle in blue, then we can see that we're working with the second proton in phosphoric acid.

01:53 So if phosphoric acid released its first proton, we would be left with h2po4 minus, h2po4 minus.

02:13 And then if we put a sodium on that, we would get to this...

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