Acids, Bases and Buffers

Question 1

Define an acid

Answer 1

Proton donor

Question 2

Define a base

Answer 2

Proton acceptor

Question 3

Give an example of a monobasic acid

Answer 3

HCl

Question 4

Give an example of a dibasic acid

Answer 4

H2SO4

Question 5

Give an example of a tribasic acid

Answer 5

H3PO4

Question 6

Identify the acid-base pairs for the below reaction:
CH3COOH + H2O <———> CH3COO- + H3O+

Answer 6

A1 B2 <———> B1 A2

Question 7

Define strong acid

Answer 7

Acid that completely dissociates

Question 8

Give some examples of strong acids

Answer 8

HCl
H2SO4
HNO3

Question 9

What is the difference between concentrated and strong

Answer 9

concentration means many mol per dm3 whereas strong refers to amount of dissociation

Question 10

Define weak acids

Answer 10

Acids that only partially dissociate

Question 11

Give some examples of weak acids

Answer 11

Any organic acid

Question 12

What is the constant used to measure the extent of acid dissociation called

Answer 12

Acid dissociation constant (Ka)

Question 13

Write the acid dissociation constant expression

Answer 13

[Ka] = [H+][A-]/[HA]

Question 14

What does a larger Ka value mean

Answer 14

Greater extent of dissociation

Question 15

equation to convert Ka to pKa

Answer 15

pKa= -log[Ka]

Question 16

Equation to convert pKa to Ka

Answer 16

Ka=10^-pKa

Question 17

What is the relationship between pKa and the strength of the acid

Answer 17

smaller the pKa the stronger the acid

Question 18

Equation to convert [H+] to pH

Answer 18

pH= -log[H+]

Question 19

Equation to convert pH to [H+]

Answer 19

[H+]= 10^-pH

Question 20

What is the relationship between pH and [H+]

Answer 20

High pH means low [H+]

Question 21

Write equation to calculate [H+] of a weak acid

Answer 21

√[Ka][HA]

Question 22

What assumption can be made when calculating pH of weak acid

Answer 22

[H+]=[A-]

Question 23

Write an expression for the ionic product of water , Kw

Answer 23

Kw = [H+][OH-]

Question 24

What is the units for Kw

Answer 24

Mol2dm-6

Question 25

What is the value of Kw at 298K

Answer 25

1x10-14

Question 26

What physical factors affect Kw and how

Answer 26

Only temperature, if increased equilibrium moves right so Kw increases and pH of pure water decreases

Question 27

Indices of [H+] and [OH-] always add up to what

Answer 27

-14

Question 28

Define the term strong base

Answer 28

Base the dissociates 100% in water

Question 29

Give some examples of strong bases

Answer 29

NaOH KOH Ca(OH)2

Question 30

Give example of weak base

Answer 30

Ammonia

Question 31

Write the equation to calculate [H+] of strong bases

Answer 31

[H+]= Kw/ [OH-]

Question 32

Define a buffer

Answer 32

A mixture that minimises pH changes on addition of small amounts of acid or base

Question 33

What are two ways in which buffers can be made

Answer 33

Weak acid and its conjugate base Weak acid and a strong alkali

Question 34

Which way does equilibrium shift when acid is added to a buffer solution and why

Answer 34

Equilibrium shifts to the left to minimise increase of [H+], forming more [HA]

Question 35

In which direction does equilibrium shift when alkali is added to a buffer solution and why

Answer 35

Equilibrium shifts to the right to minimise decrease in [H+] [H+] + [OH-] -------> H2O

Question 36

Define the term equivalence point

Answer 36

The point at which the exact volume of base has been added to just neutralise the acid

Question 37

What are the properties of a good indicator for a reaction (3)

Answer 37

Sharp colour change End point should be the same as the equivalence point Distinct colour change so you can tell when the end point has occured