What mass of CH3COONa must be added to 50.0 mL of 0.50 M CH3COOH to make a solution of pH
6.0 ?
Use the Henderson-Hasselbalch equation, substitute pKa for CH3COOH and (CH3COOH) for acid, solve for base, then convert to grams. Post your work if you get stuck.
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To solve this problem, we need to use the concept of acid-base equilibrium and the Henderson-Hasselbalch equation. The equation is given by:
pH = pKa + log([A-]/[HA])
where:
pH is the desired pH of the solution
pKa is the dissociation constant of the acid
[A-] is the concentration of the conjugate base
[HA] is the concentration of the acid
In this case, CH3COOH is a weak acid, and CH3COONa is the conjugate base. We need to determine the mass of CH3COONa required to achieve a pH of 6.0.
Step 1: Calculate pKa
The pKa for acetic acid (CH3COOH) is 4.76.
Step 2: Calculate the concentration of [A-] and [HA]
Given that the volume of the solution is 50.0 mL and the concentration of CH3COOH is 0.50 M, we can calculate the concentration of [HA] and [A-]. Since acetic acid is a weak acid, we can assume that the concentration of [HA] will be equal to the initial concentration of CH3COOH, which is 0.50 M. The concentration of [A-] can be calculated using the equation
[A-] = [HA] * 10^(pH - pKa)
Substituting the values, we have:
[A-] = 0.50 * 10^(6.0 - 4.76)
Step 3: Calculate the moles of CH3COONa required
We know that moles = concentration * volume in liters. So, the moles of CH3COOH needed can be calculated as follows:
moles of CH3COOH = [HA] * volume
moles of CH3COONa = [A-] * volume
Step 4: Calculate the molar mass of CH3COONa
The molar mass of CH3COONa can be found by summing up the atomic masses of the elements in the compound. The atomic masses are:
C = 12.01 g/mol
H = 1.01 g/mol
O = 16.00 g/mol
Na = 22.99 g/mol
Step 5: Calculate the mass of CH3COONa
The mass of CH3COONa can be calculated as follows:
mass of CH3COONa = moles of CH3COONa * molar mass of CH3COONa
Make sure to perform the calculations correctly and round the final answer to the appropriate number of significant figures.
Please note that this is a brief explanation of the process, and you may need to perform the calculations to determine the exact mass of CH3COONa.