Phosphate Buffer Concentration Calculation

In summary, the conversation discusses how to prepare 1M phosphate buffer at pH 7.8 using the given pKa value of 7.21. The person asking the question provides their attempted solution and asks for confirmation. The expert confirms that the approach is correct, but points out an error in the calculation. They also suggest using online calculators to make the process easier.
  • #1
hianghao
5
0

Homework Statement


To prepare 1M phosphate buffer pH7.8. pKa=7.21. How much molar of Na2HPO4 and NaH2PO4 to be added
I have no confidence in my answer... Can anyone pls have a check?

Homework Equations


pH=pKa+lg (base/conjugate acid)

The Attempt at a Solution


7.8=7.21 +lg (a/b)
0.59=lg (a/b)
a/b=3.89
a+b=1-----1
a=1-b -----2
(1-b)/b=3.89
b=0.2045 -Na2HPO4
a=0.7955 -NaH2PO4

Is my way of doing it correct? Did i forget to calculate other things that i must?
 
Last edited:
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  • #2
Your approach is correct. But:

hianghao said:
a/b=3.89
a+b=1-----1

OK

(1-b)/b=1

Check your math.

--
 

What is a phosphate buffer?

A phosphate buffer is a solution made up of a weak acid and its conjugate base, which helps to maintain a stable pH in biological and chemical systems. In biological systems, phosphate buffers are important for maintaining the pH of cells and bodily fluids.

Why is phosphate buffer calculation important?

Phosphate buffer calculation is important because it allows scientists to create a solution with a specific pH that is necessary for their experiments or procedures. It also helps to ensure that the pH remains stable throughout the experiment.

How is a phosphate buffer calculated?

A phosphate buffer is calculated by using the Henderson-Hasselbalch equation, which takes into account the pKa (acid dissociation constant) and the concentrations of the weak acid and its conjugate base. The formula is pH = pKa + log([conjugate base]/[weak acid]).

What factors can affect the phosphate buffer calculation?

The concentration of the weak acid and its conjugate base, as well as the pKa value, can affect the phosphate buffer calculation. Temperature and ionic strength can also have an impact on the buffer's ability to maintain a stable pH.

How can I prepare a phosphate buffer solution?

To prepare a phosphate buffer solution, you will need to know the desired pH, the pKa of the weak acid, and the concentrations of the acid and its conjugate base. Using the Henderson-Hasselbalch equation, you can calculate the amount of each component needed to achieve the desired pH. Then, mix the components in the correct proportions and adjust the solution to the desired final volume.

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