Explain how to prepare 1L of a buffer at pH 7.4 using 1M hypochlorous acid (Ka = 3.5 x 10-8) and a 1 M NaOH solution. Indicate the volume of hypochlorous acid and sodium hydroxide to use.
pka=-log(3.5 x 10^-8)=7.46
pH=pKa+ log ([A-]/[HA]),
solve for [A-]/[HJA]
10^(pH-pKa)=[A-]/[HJA]=0.879
1-0.879=0.121=[A-]
As Dr. Bob222 would say, add 121mL of NaOH solution to a volumetric flask, and add HClO to the 1,000mL mark of a 1,000mL volumetric flask.
Replace HJA with HA in the above post.
To prepare a 1L buffer solution at pH 7.4 using 1M hypochlorous acid (HOCl) and 1M sodium hydroxide (NaOH), you will need to calculate the amounts of these two solutions to mix together.
Step 1: Calculate the moles of HOCl needed.
We know that the acid dissociation constant (Ka) of HOCl is 3.5 x 10^-8. Since we want to prepare a buffer at pH 7.4, we can calculate the pKa, which is equal to the negative logarithm of the Ka: pKa = -log(Ka). Thus, pKa = -log(3.5 x 10^-8) = 7.46.
The desired pH of the buffer is 7.4, which is close to the pKa of HOCl. In a buffer solution, the ratio of [A-]/[HA] (where A- is the conjugate base and HA is the weak acid) should be approximately 1. By using the Henderson-Hasselbalch equation, we can write:
pH = pKa + log([A-]/[HA])
7.4 = 7.46 + log([A-]/[HA])
Since [A-]/[HA] is approximately 1, we can simplify the equation as:
7.4 = 7.46 + log(1)
7.4 - 7.46 = 0
-0.06 = 0
This means that the concentration of [A-] should be approximately equal to the concentration of [HA]. Therefore, to achieve a pH of 7.4, we need to use equal amounts of HOCl and NaOH.
Step 2: Calculate the volume of HOCl and NaOH needed.
Since the concentration of both solutions is 1M, we can calculate the amount of moles needed using the formula:
moles = concentration (M) × volume (L)
To prepare a 1L buffer, we need to use equal amounts (x) of HOCl and NaOH.
Moles of HOCl = 1M × x
Moles of NaOH = 1M × x
Since the moles of HOCl and NaOH are equal, we can set up an equation:
1M × x = 1M × x
x = 1
So, we need to use 1L each of HOCl and NaOH to prepare a 1L buffer solution at pH 7.4.
To summarize:
To prepare a 1L buffer at pH 7.4 using 1M HOCl and 1M NaOH, you need to mix 1L of HOCl and 1L of NaOH.