Chem 14BL wk 5-8

Question 1

Buffer solution composition

Answer 1

must consist of a weak acid and its conjugate base (or a weak base with its conjugate acid)

Question 2

How can pH stabilization be achieved?

Answer 2

Buffer must be in an excess amount; the amount of strong acid (or base) added should be in a limited amount

Question 3

Purpose of a buffer solution

Answer 3

to resist a change in pH when a strong acid or a strong base is added to the buffer solution
(In order for the buffer solution to neutralize the strong acid or strong base added, the buffer must be in an excess amount)

Question 4

Two limitations of Henderson-Hasselbalch Equation

Answer 4

1. Only applies to buffer solutions

2. K(a) for the weak acid is less than or equal to 10 ^-5

Question 5

what happens when the pH= pK(a) of a buffer solution that consists of a weak acid (HA) and its conjugate base (A-)?

Answer 5

[HA] = [A-]; this case is referred to as the optimal buffer (“best buffer”)

Question 6

Acid/Base Titrations is a technique also known as

Answer 6

Volumetric Analysis

Question 7

Define “Titrant”

Answer 7

solution of known concentration (usually placed in buret)

Question 8

Define “analyte solution”

Answer 8

solution of unknown concentration (usually placed in beaker or Erlenmeyer flask)

Question 9

Defintion of Titration Curves (aka pH curve)

Answer 9

plot of the pH of the analyte solution against the volume of titrant added during a titration

Question 10

Does equilibrium lie within all points of the titration curve?

Answer 10

Yes, EXCEPT at the instant at which the titrant is initially added

Question 11

Along the titration curve, significance of the “Initial Point”

Answer 11

no titrant is added; the solution consists only of the analyte

Question 12

Along the titration curve, significance of the “Buffer Region”

Answer 12

consists of a buffer solution (weak acid/ conjugate base or weak base/conjugate acid); contains the half-equivalence point

Question 13

Along the titration curve, significance of the “Half Equivalence Point”

Answer 13

optimal buffer conditions (aka best buffer)

pH = pK(a) or [HA] = [A-]

Question 14

Along the titration curve, significance of the Equivalence Point”

Answer 14

moles of acid = moles of base
acid and base completely react
MV = MV or n(acid) = n(base)

Question 15

Along the titration curve, significance of the “After Equivalence Point”

Answer 15

excess titrant is added

Question 16

What is Hydrolysis?

Answer 16

A reaction with water

Question 17

In terms of pH or pOH calculations, when is it significant to take into account hydrolysis in a titration curve?

Answer 17

The places on the titration curve where hydrolysis equilibria are important include the following: initial point, near the equivalence point (or the equivalence point), in the buffer region

Question 18

Final products of Strong Acid with Strong Base

Answer 18

pH = 7

final products are water and a neutral salt

Question 19

Final products of Weak Acid with Strong Base

Answer 19

pH > 7; finale products are water and the conjugate base of the weak acid;
hydrolysis of the conjugate base produces OH-

Question 20

Final products of Strong Acid with Weak Base

Answer 20

pH < 7; final products are water and the conjugate acid of the weak base
hydrolysis of the conjugate acid produces H+

Question 21

What is an Acid? What is a Base?

Answer 21

Acid: a proton donor
Base: a proton acceptor

Question 22

Strong versus Weak (Base or Acid)

Answer 22

Stron means complete dissociation

Weak means incomplete dissociation

Question 23

Titration of a weak acid with a strong base

Answer 23

Titrant: Strong Base
Analyte: Weak Acid
Initial point pH: less than 7
Equivalence point pH: greater than 7

Question 24

Titration of a weak base with a strong acid

Answer 24

Titrant: Strong Acid
Analyte: Weak Base
Initial point pH: greater than 7
Equivalence point pH: less than 7

Question 25

Titration of a strong acid with a strong base

Answer 25

Titrant: Strong Base
Analyte: Strong Acid
Initial point pH: less than 7
Equivalence point pH:equal to 7

Question 26

Titration of a strong base with a strong acid

Answer 26

Titrant: Strong Acid
Analyte: Strong Base
Initial point pH: greater than 7
Equivalence point pH: equal to 7

Question 27

ICE Box

Answer 27

Initial Change Equilibirum
used to show reactions with water;
used at the initial point and to show the hydrolysis of the conjugate acid (or base)

Question 28

SRFC Box

Answer 28

Start (in moles) Reacting (moles) Final (moles) Concentration (molarity)
used to show acid-base reactions (make sure to convert to moles)

Question 29

K(a) + K(b) = K(w)

Answer 29

acid dissociation constant
base dissociation constant
dissociation constant of water

Question 30

(titrations) When is an approximation valid?

Answer 30

If K(a) is less than or equal to 10 ^-5, we can use the approximation method.
The 5% Rule: In order for an approximation to be valid, the % ionization must be 5% or less