Question

1. In order to determine which is the best indicator to use, you need to calculate the pH at the equivalence point of the titration of KHP with NaOH.

Suppose you start with 50.0 mL of a 0.060 M solution of KHP and you titrate with 0.1000 M NaOH. What is the pH at the equivalence point?  Recall that at the equivalence point, all of the moles of acid have been converted to base.

2. Calculate the volume in mL of 10 F NaOH required to produce 1 L of 0.1 F NaOH.

3. What is the purpose of placing KHP in the oven?

	a) To remove water that would affect the mass.
	b) To remove CO2.
	c) To waste time.
	d) To heat up the sample. 4. What is the pH at the equivalence point of the titration of NaOH with HCl? 5. Which of the following can cause error in determining the equivalence point of a titration? Select all of the correct answers. a) Adding a large amount of indicator to your titration flask. b) Choosing an indicator whose color change does not exactly match the equivalence point of the substance being titrated. c) Picking the wrong indicator 6. A primary standard is a substance with high purity, high molar mass, and can easily be dried and weighed. True or false? Need help with these 6 questions.. Thank you!!

Answer 1

1. moles of KHP = 0.06 M x 0.05 L = 0.003 mols

Volume of NaOH required o reach equivalence point = 0.003 mols/0.1 M = 0.03 L

At equivalence point all of acid has been neutralized with added base to produce salt,

[KHPsalt] = 0.003 mols/(0.05 + 0.03) L = 0.0375 M

salt hydrolyzes to produce KHP and OH-.

let x amount has hydrolyzed,

Kb = Kw/Ka = [KHP][OH-]/[KHPsalt]

1 x 10^-14/3.98 x 10^-6 = x^2/0.0375

x = [OH-] = 9.705 M

pOH = -log[OH-] = 5.01

pH = 14 - pOH = 8.99

2. 10 M NaOH to 0.1 M NaOH

using,

M1V1 = M2V2

M1 = 10 M

V1 = ?

M2 = 0.1 M

V2 = 1 L

so,

volume of 10 M NaOH required = V1 = 0.1 x 1/10 = 0.01 L

3. Purpose of placing KHP in oven,

a) To remove water that would affect the mass.

4. pH at the equivalence point of titration of NaOH and HCl is neutral pH = 7.0

5. The possible cause in determining equivalence point would be,

a) Adding a large amount of indicator to your titration flask.

c) picking the wrong indicator

6. A primary standard is a substance with high purity, high molar mass, and can easily be dried and weighed : True