01.
|
i |
Ii |
iii |
iv |
v |
|
D |
C |
B |
A |
B |
02.
i)
Chemical formula is a representation that uses symbols to
show the proportions of the elements in a chemical compound.
ii)
A radical is a group of atoms with unpaired electrons. OR A radical is a
group of atoms which act as a single element in bonding.
iii)
Electrovalent bond is a chemical bond formed between metal
and non-metal by transfer of electrons.
iv)
Covalent bond is a chemical bond formed between
non-metals by sharing of electrons.
03. Differences between electrovalent and
covalent bond
|
Electrovalent
(ionic) bond |
Covalent
bond |
|
It is formed
between metals and non-metals by transfer of electron(s) |
It is formed
between non-metals by sharing of electrons. |
|
It is held by
electrostatic force of attraction |
It is held by the
weak Van der Waal force |
|
Ionic compounds
are good conductor of electricity |
Covalent
compounds are poor conductor of electricity |
|
They have high
boiling and melting points |
They have low
melting and boiling points |
|
Ionic compounds
are soluble in water |
Covalent
compounds are soluble in polar solvents |
04. (a) Oxidation
number is the measure of the electron control that an atom has in a
compound compared to the atom in the pure element.
(b)
i. Cr2O72-
2Cr + (-2 x 7) = -2
2Cr – 14 = -2
2Cr = -2 + 14
2Cr = +12 (dividing by 2
both sides)
Cr = +6
The
oxidation number of Cr is +6
ii. SO32-
S + (-2 x 3) = -2
S -6 = -2
S = -2 + 6
S = +4
The
oxidation number of S is +4
iii. KClO3
+1 + Cl + (-2 x 3) = 0
Cl -5 = 0
Cl = +5
The
oxidation number of Cl is +5
iv. NO2-
N + (-2 x 2) = -1
N – 4 = -1
N = -1 +4
N = +3
The
oxidation number of N is +3
v. NaCl
+1 + Cl = 0
Cl = -1
The
oxidation number of Cl is -1
05.
i)
FeCl3
– Iron (III) chloride
ii)
FeCl2
– Iron (II) chloride
iii)
Cu2S
– Copper (I) sulphide
iv)
N2O4
– Dinitrogen tetraoxide
v)
SF6
– Sulphur hexafluoride
06.
|
Common name |
Chemical name |
Chemical formula |
|
Common salt |
Sodium chloride |
NaCl |
|
Baking soda |
Sodium hydrogencarbonate |
NaHCO3 |
|
Soda ash |
Sodium carbonate |
Na2CO3 |
|
Chalk |
Calcium carbonate |
CaCO3 |
07. (a)
i)
Empirical formula is the formula which represent a smallest
ratio of the atoms or ions in a compound.
ii)
Molecular formula is the formula which shows the actual
number of each different atom in a molecule.
(b)
|
Element’s symbol |
C |
S |
|
Percentage
composition Percentage
composition divided to relative atomic mass Divide each value
to smallest ratio |
15.8 15.8/12 1.32 1.32/1.32 1 |
84.2 84.2/32 2.63 2.63/1.32 1.992 ≈ 2 |
The empirical formula is CS2
From,
(Empirical formula)n = Molecular formula
(CS2)n = 152
76 n = 152
n= 2
(CS2) x 2 รจ C2S4
The molecular formula is C2S4
