Chapter 16

Question 1

a buffer consists of what

Answer 1

weak acid and its conjugate base/ weak base and its conjugate acid

Question 2

hasselbalch equation

Answer 2

pH=pKa+logCB/CA

Question 3

Kw value

Answer 3

10^-14

Question 4

At same total concentration,
buffer capacity is greatest
near pKa. explain in simpler terms

Answer 4

At the midpoint of a buffer’s effective range, which is around the pKa value of the weak acid component of the buffer, the buffer capacity is highest. This is because at this point, the concentrations of the weak acid and its conjugate base are approximately equal, maximizing their ability to neutralize added acid or base without significant changes in pH.

As you move away from the pKa value in either direction, the buffer capacity decreases because one component of the buffer becomes dominant, leading to a less effective resistance against pH changes

Question 5

What change will be caused by the addition of a small
amount of HCl to a HF/NaF buffer?

Answer 5

the F^- will decrease and HF will increase.

Question 6

You dissolve 0.200 moles of solid sodium fluoride (NaF) in 1.00L of 0.150 M hydrogen fluoride solution. Determine the equilibrium pH and
fluoride ion concentration at 25oC. Ka(HF) = 6.3 x 10-4

Answer 6

pH=3.33
flouride ion= 0.200M

Question 7

You add 0.100 L of 1.0M HCl solution to 0.900 L of 0.500M NH3 solution. Determine the equilibrium pH and concentration of NH3 at
25oC. Kb(NH3) = 1.8 x 10-5

Answer 7

pH= 9.80
[NH3]= 0.350M

Question 8

You dissolve 0.200 moles of solid sodium fluoride (NaF) in 1.00L of 0.150 M hydrogen fluoride solution. Determine the equilibrium pH at
25oC. Ka(HF) = 6.3 x 10-4

Answer 8

pH=3.33

Question 9

Determine the pH of a solution containing 0.50 mol of CO32- after 0.2 mol of HCl were added. pKa(HCO3-) = 10.33

Answer 9

pH=10.51

Question 10

Given a buffer solution of 0.1 L containing 0.1M NH4Cl and 0.2M NH3, what is the buffer capacity when adding HCl to this solution?

Answer 10

0.02mol

Question 11

What is the buffer capacity of 0.8L of a 0.1M CH3COONa / 0.1M CH3COOH solution after addition of 0.02 mol of HCl towards further HCl addition?

Answer 11

0.06mol

Question 12

Higher concentration = higher buffer capacity
* Larger volume = higher buffer capacity

Answer 12

higher concentrations of both components lead to higher buffer capacity because there are more molecules available to react with added acid or base, thereby resisting changes in pH more effectively.
In a larger volume of buffer solution, there are more molecules of the weak acid and its conjugate base present. Therefore, even if the concentrations are the same, the total number of molecules available to react with added acid or base is higher in a larger volume, leading to a higher buffer capacity

Question 13

what is the effective pH range

Answer 13

pKa+/- 1

Question 14

Given a 1.0L solution of 0.1M HCOONa, how much formic acid HCOOH do you need to add to obtain a buffer of pH = 4.2? pKa(HCOOH) = 3.75, T = 25oC, neglect volume of HCOOH

Answer 14

nCA= 0.04moles

Question 15

what is the capacity of a buffer

Answer 15

the amount of acid or base it ca effectively neutralize

Question 16

buffering action

Answer 16

the reaction between a buffer and a strong acid or base added

Question 17

What mass of ammonium chloride (M = 53.491 g mol-1)
must be added to a 0.500 L solution of 0.250 mol L-1
ammonia to make a buffer with a pH of 9.26? (4 min)
Kb (NH3) = 1.8 x 10–5

Answer 17

6.69g