Question

1. Why do you need to use KHP to standardize a solution of NaOH?

2. Why isn’t it necessary to know the exact amount of water added to the sample?

3. Compare the titration curves for the weak acid and the strong acid. What are the differences?

4. The equivalence points of two titration curves are not in the same pH range. Explain.

5. Write a balanced equation for a neutralization reaction of H2SO4 with NaOH. What volume of 6 M H2SO4 would be required to neutralize 500 mL of 0.5 M NaOH?

Answer 1

1)

Standarization is important since we need to be sure of the concnetrations used; therefore, we use KHP for exact wight (its easier to calculate mass than concnetrations)

2)

because we already know the amount of MOLES used of KHP in the mix

3)

weak acid = you will expect a buffer region, where addition of volume will not change drastically compared with the STRONG acid.

The pH in the equivalent point of a stgrong acid titration is always pH = 7, neutral; whereas the weak acid has alwys a pH greater than 7, that is, basic due to the autoionization with water

4)

if the pH are not in the same ranges, this means that the pKa values fo eac weak acid is different, therefore, each will re-ionize with water differently

5)

H2SO4 + 2NaOH = Na2SO4 + 2H2O

mol of acid = mol of base

mol of base = MV = 500*0.5 = 250 mmol of base

then we need 1/2 of that

250/2 = 125 mmol of acid needed

M = mmol/mL

mL = mmol/M = 125/6 = 20.8333 ml of acid is needed