Question

How would you make a 1.0l of 0.1m buffer solution at ph 4? (there are many possible solutions!)

Answer 1

To make a 1.0 L of 0.1 M buffer solution at pH 4, you will need to choose a weak acid and its conjugate base that have a pKa close to 4, such as acetic acid (CH3COOH) and sodium acetate (CH3COONa). Calculate the moles and mass of each compound needed, then dissolve them in distilled water to make up the final volume.

Step-by-step explanation:

To make a 1.0 L of 0.1 M buffer solution at pH 4, you will need to choose a weak acid and its conjugate base that have a pKa close to 4. The most common buffer system for pH 4 is the acetic acid (CH3COOH) and sodium acetate (CH3COONa) system. Here's how you can prepare the buffer:

1. Calculate the amount of acid and conjugate base needed using the Henderson-Hasselbalch equation:

pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the conjugate base and [HA] is the concentration of the acid. Rearrange the equation to solve for the concentrations, given that you want a 0.1 M buffer:

0.1 = 4 + log([A-]/[HA])

[A-]/[HA] = 10^(0.1 - 4) = 10^(-3.9)

1. Choose a volume for the buffer solution. In this case, we want 1.0 L.
2. Calculate the moles of acid and conjugate base needed using the volumes and concentrations:

moles = volume (L) * concentration (M)

For the acid:

moles of acid = 1.0 L * 0.1 M = 0.1 mol

For the conjugate base:

moles of base = 1.0 L * 10^(-3.9) M = 10^(-3.9) mol

1. Calculate the mass of each compound needed using their molar masses:

For the acid:

mass of acid = moles of acid * molar mass of acid

For sodium acetate:

mass of base = moles of base * molar mass of base

1. Measure the calculated masses of each compound and dissolve them in distilled water to make up a final volume of 1.0 L.The resulting solution will be a 1.0 L of 0.1 M buffer solution at pH 4.