I have already posted this and never got a response, please help.
here is my data from lab:
Buffer1: HPO4- weight 3.412g; original pH
Buffer 2: HEPES wt: 1.090g original pH 10.08
buffer1:
pH of 0.1M: 7.5;
pH of 0.01: 7.72;
pH of 0.001M: 7.87
buffer2:
PH of 0.1M: 7.5
ph of 0.01 M: 7.42
pH of 0.001M: 7.42
The problem will be done for one of the buffers made.
A) What is the ratio of A-/HA in your buffer after you adjusted its pH to the required value? (pH goal: 7.5)
B) How many micromoles of A- and HA are present in the solution?
C) If you now add 3 mL of 1 M NaOH, will you still have a valid buffer?
If necessary, here are the pka values and molecular weights: HEPES: pka 7.55; mw= 238.3; phosphate (HPO4-) pka1: 2.12 pka2: 7.21; pka 3: 12.32; mw=142.0
HERE ARE HINTS I HAVE BEEN GIVEN:
A. Use the Henderson Hasselbach equation.
B. micromole = 0.001 mole
you know that the HA + A- have to equal number of moles in the 0.1 M solution
C. Will all of the HA form to the A- form be converted? Or will some of it remain?
Thank you very much!!!
To solve this problem, we need to use the Henderson-Hasselbalch equation, which relates the pH of a buffer solution to the ratio of the concentrations of its acid (HA) and its conjugate base (A-):
pH = pKa + log([A-]/[HA])
Let's go step by step to answer each part of the question:
A) What is the ratio of A-/HA in your buffer after you adjusted its pH to the required value? (pH goal: 7.5)
To find the ratio of A-/HA, we can rearrange the Henderson-Hasselbalch equation:
[A-]/[HA] = 10^(pH - pKa)
For Buffer 1, the pKa is not provided, so we need to use the pKa value for phosphate (HPO4-), which is 12.32. Substitute the values:
[A-]/[HA] = 10^(7.5 - 12.32)
Solving this equation will give you the ratio of A-/HA for Buffer 1.
B) How many micromoles of A- and HA are present in the solution?
To determine the number of micromoles (µmol) of A- and HA, we need to know the volume and concentration of the solution.
Assuming the volume of the solution is 1 liter (1000 mL), we can use the following formula:
Concentration (M) = (moles of solute) / (volume in liters)
To find the moles of A- and HA in the 0.1 M buffer solution, multiply the concentration by the volume. For example:
moles of A- = (0.1 M concentration of A-) * (0.001 L volume of solution)
Calculate this for both A- and HA to find the number of moles in each case. Then, convert the moles to micromoles by multiplying by 1,000.
C) If you now add 3 mL of 1 M NaOH, will you still have a valid buffer?
To determine if the buffer remains valid after adding NaOH, we need to consider the reaction between the acid (HA) and the base (OH-) in the buffer.
HA + OH- -> A- + H2O
The buffer will still be valid if the concentration of the acid (HA) is significantly higher than the concentration of the base (OH-). If the added base (OH-) consumes most of the acid (HA), the buffer capacity will be compromised.
To check if the buffer is still valid, calculate the new concentration of HA after the reaction based on the stoichiometry of the reaction and the amount of NaOH added.
Please let me know if you need any further clarification or help.