module 2

MODULE 2
12
WORKSHEET
CONCEPTS OF ACIDS
Syllabus reference 9.3.4
1
To check your understanding, fill in each of the following blanks with a word or phrase.
a
Compounds can be classified as acids or bases according to a number of different theories.
sour
Originally an acid was a substance with a __________
taste and which reacted with certain
hydrogen
metals to produce ________________
gas. Antoine Lavoisier attempted to define acids on the
chemical
basis of their ______________
composition. He proposed that acids were substances which
oxygen
contained ______________.
This theory was soon disproved because although many non-metallic
acids
metallic oxides formed bases when dissolved in water.
oxides formed __________
in water, ___________
b
Davy
hydrogen
An English chemist, Sir Humphrey _________,
suggested that acids contained ____________
salts
rather than oxygen and that acids reacted with metals to form ____________.
Bases were
water
defined as substances that reacted with acids to form salts and _______________.
c
Svante Arrhenius developed a definition to explain the properties of acids. He proposed that
hydrogen
an acid was a substance which produced ______________
ions in aqueous solution. If the acid
completely but if it was weak it ionised only ________________.
slightly
was strong it ionised _____________
hydroxide
Arrhenius defined a base as a substance which produced ________________
ions in aqueous
solution. One problem with the Arrhenius definition is that it can only be applied to
aqueous
_______________
solutions and does not allow for different solvents.
d
A more general definition was developed by the two chemists, Lowry and Brönsted.
According to the Brönsted–Lowry definition, an acid is a substance that in solution donates a
proton
acceptor
_______________. A Brönsted–Lowry base is a proton ________________. According to this
donates
conjugate
theory, the acid ______________
a proton to form its ________________
base. Similarly, a
proton
acid
base accepts a _______________
to form its conjugate __________.
A substance which can act
amphiprotic
as a proton donor and as a proton acceptor is called __________________.
Copyright © 2007 McGraw-Hill Australia
CONQUERINGCHEMISTRY HSC
MODULE 2 WS 12
2
Write equations for the following showing the formation of the hydronium ion, H3O, in aqueous
solution.
a HNO3
HNO3  H2O → H3O  NO3
b
HF
HF  H2O → H3O  F
c
H2CO3
H2CO3  H2O
d
HSO4
HSO4  H2O
3
4
H3O  HCO3
H3O  SO42
Write equations for the following showing their basic nature in aqueous solution.
a NaOH
NaOH → Na  OH
b
HS
HS  H2O → H2S  OH
c
NH3
NH3  H2O → NH4  OH
d
KHCO3
KHCO3  H2O → K  H2CO3  OH
Give the conjugate bases of the following acids.
a NH4
NH3
b
HCN
CN
Copyright © 2007 McGraw-Hill Australia
CONQUERINGCHEMISTRY HSC
MODULE 2 WS 12
c
H3O
H2O
d
HOBr
OBr
5
Give the conjugate acids of the following bases.
a Cl
HCl
b
CN
HCN
6
c
HPO42
H2PO4
d
N2H4
N2H5
For each of the following reactions, identify the acid on the reactant side of the equation and its
conjugate base.
a HCOOH  CO32 HCOO  HCO3
�
��������������
����� �������
�
��
����
����������
�
�
����������� �
�����
�
�
�
����
����
�
�
�
� ������
����������
� HCN
�����
b�� CN
��
H�2� O�2�����������

��
����
� HO2 �
�
�
����
�
����
���������
�
�
�
����
����
�� ����
��
� �
�
����
����
����� � ��
���������
�
�
�� ���� �
� ��
�
�� �����
������
� ��
�c
�
�
�
��
�����
� ����HNO
����
�  S2
����
����
����
����
�
�
�
HS

NO
3
�
�
� ����
�� ������ �
2
�����
���������� �
����
Copyright © 2007 McGraw-Hill Australia
����
CONQUERINGCHEMISTRY HSC
MODULE 2 WS 12
7
For each of the following reactions, identify the base in the reactant side of the equation and its
conjugate acid.
a HSO3  HS H2S  SO32
�
�
�
�
���� ����� �
�
�
����
���� �����
�
����
������������
����
��
���������
�
����
� 
�
��

�
��  CO 2
���
� �� ������
������
b�� CH
 HCO
CH
���3��O�����
������
�������
�
�
3
3OH
3
�
�
�
�
� ���� � ����
����
����
��
� ������� � ���
�����������
�
�
�
� �
��
��
����
����
��
������ � �� ���
������� � ���
���
�� ������
� ��������
�
�
�
�
��
��
�c ��
 ����
2
�����
� 3
����������
�
����
����
����
�
�PO
� HPO
NH

NH
4
4
3
4
�
� ������
��� ������ �
���� ��
����������� �
����
����
8
Tartaric acid is diprotic while citric acid is triprotic.Write equations for the stepwise dissociation
of the acids given. All acids here are weak so use appropriate arrows.
a citric acid (H3C6H5O7)
H3C6H5O7
b
H2C6H5O7
H  HC6H5O72
HC6H5O72
H  C6H5O73
tartaric acid (H2C4H4O6)
H2C4H4O6 H  HC4H4O6
HC4H4O6
c
H  C4H4O62
HOCl
HOCl
9
H  H2C6H5O7
H  OCl
HCO3 is amphiprotic. Write one equation to show it acting as an acid and another to show it
acting as a base.
Base
HCO3  H2O
H2CO3  OH
Acid
HCO3  H2O
H3O  CO32
Copyright © 2007 McGraw-Hill Australia
CONQUERINGCHEMISTRY HSC
MODULE 2 WS 12
10 Write the formula of each of the following salts and classify it as acidic, basic or neutral.
a potassium acetate
KCH3COOK basic
b
sodium nitrate
NaNO3
c
potassium cyanide
KCN
d
neutral
ammonium bromide
NH4Br
f
basic
sodium sulfate
Na2SO4
e
neutral
acidic
potassium carbonate
K2CO3
basic
Copyright © 2007 McGraw-Hill Australia
CONQUERINGCHEMISTRY HSC
MODULE 2 WS 12