Question

You are to make 90.0 mL of a 0.27 M buffer at ph 7.20 using the acid form of the Good buffer EPPS (MW = 252.332 g / mol, pKa = 8.00)

Questions:

1. Using the molarity, volume, and molecular weight, calculate how many grams of solid EPPS you need to weigh out?

2. Using the Henderson-Hasselbalch equation and the information given, calculate the value of [A-] / [HA]

3. Using the value of [A-] / [HA] calculated in question 2 and the concentration given at the beginning (Conc.), solve for x in this equation:

[A-] / [HA] = x / (Conc. -x)

4. The unknown x is in units of Molar. Given the volume from the beginning, how many moles of NaOH would this be?

5. Calculate how many mL of a 1 M NaOH solution you would need for the number of moles calculated in the previous question.

When making a buffer using two solutions - one of the conjugate acid, one of the conjugate base - the calculations are very similar.

You are to make 100.0 mL of a 0.50 M acetate buffer ( pKa = 4.72) at ph 5.00 using 0.50 M stocks of acetic acid and sodium acetate

6. Using Henderson-Hasselbalch and the information given, calculate the value of [A-] / [HA]

7. Reuse the equation from questions 3, but in place of Conc. use the final volume (100 mL) of the solution. The unknown (x) is now the volume of base form we need to add. Using [A-] / [HA] calculated in questions 6 and the equation shown, solve for x.

8. If the final volume is the total of the acid and base solutions, how many mL of the acid form do you need to combine with the base form in the previous question?