Question

To a 25mL cylinder add 1.25mL of a 2M stock solution of Trizma base. Calculate the concentration of the Tris-base in your cylinder if the final volume is filled with 25ml water.             ( 1 mark)

Calculate the ratio of Tris- base to Tris-acid required, using the Henderson- Hasselbach equation.             (2 marks)

You are provided with a 1M Tris- HCL solution. Using a Tris buffer concentration of 100mM and ratios from step 2 above, calculate the concentration of Tris HCl required and the concentration of Tris base required.                                                (4 marks)

Determine by calculation the volume of Tris HCl required and the volume of Tris base needed to make a 100mM of a 1L buffer solution using your data from step 3 and your Tris solution from step 1.            (5 marks)

Answer 1

Answer 2

Solution :

3) According to molarity equation,

M1V1 = M2V2

Given,

M1 = concentration of stock solution = 2M

V1 = volume of stock solution =1.25 mL

M2 = concentration of final solution = 25 mL + 1.25 mL = 26.25 mL

Thus,

M2 = M1V1/V2

M2 = 2.0 M x 1.25 mL / 26.25 mL

M2 = 0.09524 M

Therefore,

Concentration of final solution = 0.09524 M

4) Ratio of tris base to tris acid = 0.50

Calculation:

According to Hendersen Hasselbalch equation,

pH = pka + log [tris base] /[tris-acid]

7.8 = 8.1 + log [tris base]/[tris acid ]

log [tris base] /[tris acid] = -0.3

[tris base]/ [tris acid] = antilog (-0.3)

[tris base ] / [tris acid] = 0.50