This is my third time to ask this and no one has answered. Please help.
An enzyme-catalyzed reaction is carried out in a 50-mL solution containing 0.1 M TRIS buffer. The pH of the reaction mixture at the start was 8.0. As a result of the reaction, 0.002 mol of H+ were produced. What is the ratio of TRIS base to TRIS acid at the start of the experiment? What is the final pH?
If needed: TRIS(Trizma base) mw= 121.1; pka= 8.3; TRIS-HCl mw= 157.6; pka= 8.3
I kind of have an idea. I start out with the hendersn hasselbalch equation and solve for the ratio ([Tris] / [Tris HCl]). I need help doing this first before i can proceed with the rest of the problem.
Thank you very much.
here is how to solve the problem, put I need help following these instructions. would you show me the math step by step, so I could understand?
Here is how to solve the problem:
Use the Henderson-Hasselbalch equation.
pH = pKa + log ([Tris] / [Tris HCl]). Here the pH is 8 and the pKa of the Tris is 8.3, so you can solve for the ratio ([Tris] / [Tris HCl]).
After the reaction, when 0.002 moles of H+ were produced, this H+ will CONSUME the Tris base to FORM more Tris HCl From the first part of the problem you have the ratio ([Tris]/ [Tris HCl]) = ???. You also know you have 50mL of 0.1M Tris buffer, or 0.005 moles of total Tris (in acid or base forms), which can be written out as "moles Tris + moles TrisHCl = 0.005. Combine this with the equation for the ratio, and solve to find # of moles of both the base and acid form. This will tell you how many moles of acid and base form Tris you had BEFORE the reaction.
Now subtract 0.002 moles from the amount of Tris base, and add 0.002 moles to the amount of TrisHCl you calculated (the H+ consumes base, makes TrisHCl). Now using the same pKa, and the new calculated concentrations of Tris and TrisHCl, you can again use the Henderson Hasselbalch equation, this time solving for pH, the final pH
Thank you.
To solve this problem, we can use the Henderson-Hasselbalch equation, which relates the pH of a solution to the ratio of the concentrations of the conjugate acid and base forms of a buffer:
pH = pKa + log([A-]/[HA])
In this case, TRIS acts as a buffer, where TRIS base is the conjugate base (A-) and TRIS acid (TRIS-HCl) is the conjugate acid (HA).
Let's start by finding the ratio of TRIS base to TRIS acid at the start of the experiment:
1. We can use the given information that the pH of the reaction mixture at the start was 8.0. The pKa of TRIS is also given as 8.3.
2. Substituting these values into the Henderson-Hasselbalch equation, we get:
8.0 = 8.3 + log([A-]/[HA])
3. Rearranging the equation, we have:
log([A-]/[HA]) = 8.0 - 8.3
log([A-]/[HA]) = -0.3
4. Taking the antilog of both sides of the equation, we get:
[A-]/[HA] = 10^(-0.3)
[A-]/[HA] = 0.501
The ratio of TRIS base to TRIS acid at the start of the experiment is approximately 0.501.
Now, let's determine the final pH of the reaction mixture:
1. We are given that 0.002 mol of H+ were produced as a result of the reaction.
2. To determine the final pH, we need to calculate the change in concentration of H+ ions.
3. Since TRIS is a weak base, it reacts with the H+ ions (produced by the reaction) to form TRIS-HCl, which is the conjugate acid.
4. The molar mass of TRIS is provided as 121.1 g/mol. Using the molar mass and the amount of H+ ions produced (0.002 mol), we can calculate the mass of TRIS reacted:
Mass of TRIS reacted = molar mass of TRIS × moles of H+ ions produced
Mass of TRIS reacted = 121.1 g/mol × 0.002 mol
Mass of TRIS reacted = 0.2422 g
5. To find the final pH, we need to calculate the molarity of TRIS base and TRIS acid remaining in the 50 mL solution.
6. The initial molarity of TRIS base ([A-]) can be calculated using the ratio we found earlier:
[A-]/[HA] = 0.501
0.1 M (initial concentration of buffer) = [A-] + [HA] = [A-] + 0.501[A-]
0.1 M = [A-](1 + 0.501)
[A-] = 0.1 M / (1 + 0.501)
[A-] = 0.066173 M
7. Since TRIS is a weak base, it reacts with H+ ions to form TRIS-HCl. The moles of TRIS base reacted can be calculated using the mass of TRIS reacted:
Moles of TRIS base reacted = Mass of TRIS reacted / molar mass of TRIS base
Moles of TRIS base reacted = 0.2422 g / 121.1 g/mol
Moles of TRIS base reacted = 0.002 mol
8. The concentration of TRIS base remaining can be calculated by subtracting the moles of TRIS base reacted from the initial concentration of TRIS base:
Concentration of TRIS base remaining = [A-] - moles of TRIS base reacted / volume
Concentration of TRIS base remaining = 0.066173 M - 0.002 mol / 0.05 L
Concentration of TRIS base remaining = 0.026173 M
9. Finally, we can calculate the final pH using the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
pH = 8.3 + log(0.026173 M/0.002 M)
pH = 8.3 + log(13.0865)
pH ≈ 8.3 + 1.118 ≈ 9.418
Therefore, the final pH of the reaction mixture is approximately 9.418.