when a 25.0 mL sample of an unknown acid was titrated with a 0.100 M NaOH solution. Determine Ka for the unknown acid. Volume NaOH = 12.5 mL; pH=3.80
please help me explain in details!!!
This problem needs a lot of work. In its present form, there are too many details not known.
1. Technically, this can't be solved since we don't know if the acid is monoprotic, diprotic, or triprotic.
Assuming it is monoprotic,
HA + NaOH ==> NaA + H2O
2. The problem SHOULD say that 25.0 mL is the equivalence point OR
3. That the 12.5 mL represents titration to the half-way point. All of that information is missing.
However, if we supply that missing information, then
Ka = (H^+)(A^-)/(HA)
At the exact half-way point in the titration, (A^-) = (HA), so Ka = (H^+).
Convert pH to (H^+) and you will have Ka.
25.00 mL sample of this sulfuric acid solution. You then titrate it with a 0.1322 M potassium hydroxide solution. A volume of 41.22 mL of potassium hydroxide was required to complete the titration. What is the concentration of this unknown sulfuric acid solution?
To determine Ka for the unknown acid, you need to use the information provided and apply the principles of acid-base titration and the relationship between pH and pKa values.
First, let's break down the information given:
- Initial volume of unknown acid solution (H+): 25.0 mL
- Volume of NaOH solution required to reach the equivalence point (where moles of H+ = moles of OH-): 12.5 mL
- Concentration of NaOH solution: 0.100 M
- pH of the solution at the equivalence point: 3.80
Here's the step-by-step process to determine Ka for the unknown acid:
Step 1: Calculate moles of NaOH used in the titration.
The moles of NaOH used can be calculated using the formula:
moles of NaOH = concentration of NaOH (mol/L) x volume of NaOH (L)
In this case, the concentration of NaOH is 0.100 M and the volume used is 12.5 mL (which is 0.0125 L). Plug in these values to calculate the moles of NaOH used.
Step 2: Calculate the moles of H+ (acid) in the unknown acid solution.
Since the reaction between the acid (H+) and base (OH-) at the equivalence point is 1:1, the moles of H+ in the unknown acid solution are equal to the moles of NaOH used.
Step 3: Calculate the initial concentration of the acid.
The initial concentration of the acid can be calculated using the formula:
initial concentration of acid = moles of acid / volume of acid (L)
In this case, we have the moles of H+ (acid) from Step 2, which is equal to the moles of NaOH used. The volume of acid is 25.0 mL, which is 0.0250 L. Plug in these values to calculate the initial concentration of the acid.
Step 4: Calculate pKa using the pH at the equivalence point.
pKa is a logarithmic value that represents the acidity of the acid. It can be calculated using the formula:
pKa = pH + log ([A-]/[HA])
At the equivalence point, the concentration of A- (conjugate base) and HA (acid) is equal. Therefore, the ratio [A-]/[HA] is 1. Plug in the given pH value of 3.80 into the equation to calculate pKa.
Step 5: Calculate Ka using the pKa value.
Ka (acid dissociation constant) can be calculated using the expression:
Ka = 10^(-pKa)
Plug in the pKa value obtained from Step 4 into this equation to calculate the Ka for the unknown acid.
Remember to pay attention to the correct number of significant figures throughout the calculations and round the final answer to an appropriate number of significant figures based on the given values.
Follow these steps, and you should be able to determine the Ka for the unknown acid.