How to make 100 mL of 100mM of Tris HCl and 100 mL of 100mM of Tris Base. Follow the pH of the resulting combined solution as it is heated from 4 to 50 degrees Celsius.

Question

How to make 100 mL of 100mM of Tris HCl and 100 mL of 100mM of Tris Base. Follow the pH of the resulting combined solution as it is heated from 4 to 50 degrees Celsius.

I did not use the HH equation in this problem. I started with just converting to moles needed and then to grams. Then I was planning to add water to the mark. Since Tris is a base that's all I thought was needed.
For Tris HCl I was planning to follow the same protocol but later just to add HCl until the desired pH (dropwise). Do I have the right protocol? Also should I be using HH equation for this protocol or not?

Answer 1

Either way is appropriate, but using a procedure for such preps is more reliable. See suggested procedure and example in answer to your next question.

Answer 2

To make a 100 mL solution of 100 mM Tris HCl and Tris Base, you can start by calculating the amount of each compound needed.

1. Convert the desired concentration (100 mM) to moles per liter:
- 100 mM = 0.1 moles per liter

2. Calculate the moles needed for a 100 mL solution:
- 0.1 moles/L * 0.1 L = 0.01 moles

3. Determine the molar mass of each compound:
- Tris HCl (C4H11NO3.HCl) has a molar mass of 157.6 g/mol
- Tris Base (C4H11NO3) has a molar mass of 121.1 g/mol

4. Calculate the mass of each compound:
- Tris HCl: 0.01 moles * 157.6 g/mol = 1.576 grams
- Tris Base: 0.01 moles * 121.1 g/mol = 1.211 grams

Now you have the amount of each compound needed to make a 100 mL solution at a concentration of 100 mM.

To adjust the pH of the combined Tris HCl and Tris Base solution when heated from 4 to 50 degrees Celsius, you can use HCl dropwise to maintain the desired pH.

It is not necessary to use the Henderson-Hasselbalch (HH) equation in this protocol, as you are adjusting the pH directly with HCl rather than calculating the pH from the concentrations of Tris HCl and Tris Base.

However, if you want to calculate the pH using the HH equation, you can do so by knowing the pKa value of Tris (8.06 at 25 degrees Celsius). The HH equation relates the pH, pKa, and the molar concentrations of the acid and its conjugate base. But in your case, since you are directly adding HCl, you don't need to use the HH equation.

Keep in mind that pH can vary with temperature, so it's important to monitor and adjust the pH as the solution is heated.