classification of Substances QA
Classification
of Substances
EXERCISES
1. Write the answers to the following questions.
(a) How are properties of substances determined?
(b) Explain the differences between compounds and
mixtures
(c) Why is an alloy a mixture?
(d) Why are substances classified?
2. Fill in the blanks.
(a) In a compound the ………………. do not retain their
properties.
(b) In a …………… properties of constituents are retained.
(c) The chemical symbol of calcium is …………………… .
(d) The molecular formula for carbon dioxide is ……………………
(e) The compound sodium chloride is made from the
combination of the elements ……….. and ………
(f) In the compounds H2O, NaOH and H2O2
………….. are the common elements.
3. Given below are some compounds and the number of
atoms of their constituent elements in each of their molecules. Write their molecular
formulas.
Compound
|
Number of atoms of
constituent elements
|
formula
|
(a) Potassium hydroxide
(b) Hydrogen peroxide
(c) Iron chloride
(d) Ammonium chloride
(e) Copper sulphate
(f) Magnesium oxide
|
K:1, O:1, H:1
H:2, O:2
Fe:1, Cl:2
N:1, H:4, Cl:1
Cu:1, S:1, O:4
Mg:1, O:1
|
KOH
…………………………
…………………………
…………………………
…………………………
…………………………
|
4. Match the following.
Group
‘A’ Group
‘B’
(a) Sodium 1.
MgO
(b) Potassium 2.
FeS
(c) Iron sulphate 3.
Na
(d) Sugar 4.
K
(e) Magnesium oxide 5.
C12H22O11
6.
CO2
ANSWERS
1. Write the answers to the following questions.
(a) How are properties of substances determined?
ANS: 1) The properties
of substances are determined according to their atomic structure and atomic
number.
2)
Example: Substances classified as elements, compounds, mixtures also as metals
and non metals
(b) Explain the differences between compounds and
mixtures
ANS:
|
Compounds
|
Mixtures
|
|
1. Compound is formed by combination
of two or more elements in fixed
proportion of weight
2. A new substance is formed when two
elements combine to form compound
3. Properties of compound are different
from its constituent elements
4. constituent elements are separated
using chemical processes
example:- H2O , CO2, MgO etc
|
1. A mixture is formed by mixing of
two or more substances in any proportion
2. A new substance is not formed in a
mixture
3. Constituent elements retain their
properties in a mixture.
4. constituent elements are separated
using physical processes.
Example:- steel, air, milk etc
|
(c) Why is an alloy a mixture?
ANS: 1) When
two more substances are mixed together a mixture is formed. Alloy is a mixture
of metals
2)
Proportion of constituents in the mixture is not fixed.
3) In
an alloy two or more elements are mixed together.
4)
When they are mixed their chemical properties are changed though there is no
chemical reaction.
5)
Hence an alloy is a mixture. Example – Steel (alloy of iron and carbon), Brass(zinc
and copper)
(d) Why are substances classified?
ANS: 1)
Putting substances into groups based on their properties is called
classification of substances.
2)
Due to classification, studying them becomes easier and convenient.
3)
Example: Substances classified as elements, compounds, mixtures also as metals
and non metals
2. Fill in the blanks.
(a) In a compound the elements do not retain
their properties.
(b) In a mixture properties of
constituents are retained.
(c) The chemical symbol of calcium is Ca.
(d) The molecular formula for carbon dioxide is CO2
(e) The compound sodium chloride is made from the
combination of the elements Sodium (Na) and Chloride (Cl).
(f) In the compounds H2O, NaOH and H2O2
hydrogen (H) are the common elements.
3. Given below are some compounds and the number of
atoms of their constituent elements in each of their molecules. Write their molecular
formulas.
|
Compound
|
Number of atoms of
constituent elements
|
formula
|
|
(a) Potassium hydroxide
(b) Hydrogen peroxide
(c) Iron chloride
(d) Ammonium chloride
(e) Copper sulphate
(f) Magnesium oxide
|
K:1, O:1, H:1
H:2, O:2
Fe:1, Cl:2
N:1, H:4, Cl:1
Cu:1, S:1, O:4
Mg:1, O:1
|
KOH
H2O2
FeCl2
NH4Cl
CuSO4
MgO
|
4. Match the following.
Group
‘A’ Group
‘B’
(a) Sodium 3.
Na
(b) Potassium 4.
K
(c) Iron sulphate 2.
FeS
(d) Sugar 5.
C12H22O11
(e)
Magnesium oxide 1.
MgO
