6 – Composition of Matter
Q 1.
Fill in the blanks.
Ans.
(1) The intermolecular force is maximum in the particles of solid.
(2)
Solids retain their volume even when external pressure is applied. This property
is called elasticity.
(3)
Matter is classified into the types mixture, compound and element, by applying
the criterion chemical composition of matter.
(4)
Matter that contain two or more constituent substances is called mixture.
(5)
Milk is an example of type of matter called heterogeneous mixture.
(6)
Water, mercury and bromine are similar to each other, because the three
are liquids.
(7)
Valency of carbon is 4 and that of oxygen is 2. From this, we understand that
there are 2 chemical bond/bonds between the carbon atom and one oxygen
atom in the compound-carbon dioxide.
Q. 2
Identify the odd term.
Ans. (1) Brass. (Others are elements.)
(2)
Hydrogen. (Others are compounds.)
(3)
Carbon. (Others are mixtures.)
(4)
Petrol. (Others are inorganic compounds.)
(5)
Sugar. (Others are inorganic compounds.)
(6)
Carbon. (Others are monovalent elements.)
Q 3.
Sea water tastes salty due to the dissolved salt. The salinity (the proportion
of salts in water) of some water bodies Lonar lake - 7.9%, Pacific Ocean 3.5%,
Mediterrnean sea - 3.8%, Dead sea - 33.7%. Explain two characteristics of
mixtures from the above information.
Ans.
(1) The constituents of a mixture (the proportion of salts in water) do not
combine chemically. (2) Their constituents are present in any proportion by weight.
(3) The constituent of a mixture can be separated by a physical process.
following
table. Identify
Q 4.
Plants synthesize glucose in sunlight with the help of chlorophyll from carbon
dioxide and water and give away oxygen. Identify the four compounds in this
process and name their types.
Ans.
Photosynthesis :
6CO2 + 6H2O
light C6H1206
+ 602
Carbon Water
Chlorophyll Glucose
Oxygen dioxide
Carbon
dioxide, water, glucose, and Chlorophyll are compounds.
Types
: Organic compounds : Glucose
Inorganic
compounds : Carbon dioxide and water
Complex
compounds : Chlorophyll.
Q 5.
In one sample of brass, the following ingredients were found : copper (70%) and
zinc (30%). Identify the solvent, solute and solution from these.
Ans.
Brass is an alloy, it contains 70% copper and 30% zinc. The largest proportion
is solvent, i.e. copper. The smaller proportion is solute, i.e. zinc. The
solution is Brass.
Q 6. Give
two examples each:
(1) Liquid element.
Ans. Mercury (Hg), Bromine (Br.)
(2) Gaseous element.
Ans. Hydrogen (H), Oxygen (O2).
(3) Solid element
Ans. Iron (Fe), Copper (Cu), Silver
(Ag).
(4) Homogeneous mixture.
Ans.
Sea water, blue vitriol dissolved in water.
(5)Colloid.
Ans. Milk, blood.
(6)Organic
compound.
Ans. Glucose, urea.
(7) Complex compound.
Ans. Chlorophyll, Haemoglobin.
(8) Inorganic compound.
Ans. Soda, rust, limestone.
(9)
Metalloid.
Ans.
Silicon, arsenic.
(10) Element with valency 1.
Ans.
Sodium (Na), potassium (K), chlorine (CI).
(11)
Element with valency 2.
Ans. Magnesium (Mg), Calcium (Ca). Q 7. Write the names and symbols of the constituent elements and identify their valencies from their molecular formulae given below: KCI, HBr, MgBr2, K2O, NaH, CaCl2, CCI4, HI, H2S, Na2S, Fes, BaCl2
|
Sr
No
|
Molecular
formula |
Constituent
element/ Name symbol |
Valency |
|
1. |
KCI |
Potassium
K Chlorine
C1 |
1 1 |
|
2. |
HBr |
Hydrogen
H Bromine
Br |
1 1 |
|
3. |
MgBr2 |
Magnesium Mg Bromine
Br |
2 1 |
|
4. |
K2O |
Potassium
K Oxygen
O |
1 2 |
|
5. |
NaH |
Sodium
Na Hydrogen
H |
1 1 |
|
6. |
CaCl2 |
Calcium
Ca Chlorine
CI |
2 1 |
|
7. |
CCI4 |
Carbon
C Chlorine
CI |
4 1 |
|
8. |
HI |
Hydrogen
H Iodine I |
1 1 |
|
9. |
H2S |
Hydrogen
H Sulphur
S |
1 2 |
|
10. |
Na2S |
Sodium
Na Sulphur
S |
1 2 |
|
11. |
FeS |
Iron
Fe Sulphur
S |
2 2 |
|
12. |
BaCI2 |
Barium
Ba Chlorine
CI |
2 1 |
Q 8
Give scientific reasons :
(1)
Hydrogen is combustible, oxygen helps combustion, but water helps to extinguish
fire.
Ans.
(1) Water is a compound of hydrogen and oxygen. (2) In a compound, the
constituents do not retain their individual properties. Hence, hydrogen is
combustible and oxygen helps combustion, but water is neither combustible nor
supports combustion, it helps to extinguish fire.
(2)
The constituent substances of a colloid cannot be separated by oridinary
filtration.
Ans.
(1) A colloidal solution is heterogeneous. (2) The diameters of colloidal
particles are of the order of 10-5 m. (3) The particles of a colloid can easily
pass through a filter paper as the pore size of a filter paper is big. Hence,
the constituents of a colloidal cannot be separated by filtration.
(3)
Lemon sherbat has sweet, sour and salty taste and it can be poured in a glass.
Ans.
(1) Lemon sherbat is a mixture. It is made up of lemon juice, sugar, salt and
water. (2) Formation of lemon sherbat does not involve any chemical reaction.
(3) The constituents of sherbat retain their individual properties. Hence,
lemon sherbat is sweet, sour and salty to taste and it can be poured in a
glass.
(4) A
solid matter has the properties of definite shape and volume.
Ans.
(1) The forces among the constituent particles (atom/molecules) are called
intermolecular forces. (2) In solids these forces are strong enough to keep the
particles together in fixed positions, as a result solids have a definite shape
and volume.
Q 9. Deduce the molecular formulae
of the compound obtained from the following pairs of elements by the cross
multiplication method.
(1) C (Valency 4) and Cl (Valency
1)
Ans. Step 1: Write the symbols of the constituent elements.
C Cl
Step 2: Write the valency below
the respective elements.
C CI
4 1
Step 3: Cross multiply the valencies.
C C
4 1
The molecular
formula : CCI4
(2) N (Valency 3) and H (Valency 1)
Ans. Step 1: Write the symbols of the constituent elements.
Ν Η
Step 2: Write the valency below the respective elements.
Ν Η
3 1
1 Step 3: Cross
multiply the valencies.
Ν Η
3 1
The molecular formula
: NH3
(3) C (Valency 4) and 0 (Valency 2)
Ans Step 1: Write the symbols of the constituent elements.
C O
Step 2: Write the valency belo respective elements.
C O
4 2
Step 3: Cross multiply the valencies.
C O
4 2
The formula : C2O4
The number of constituent atoms in the final molecular
formula should be the smallest possible whole number. Divide the formula C2O4 by
suitable number.
Final molecular formula obtained by dividing by 2.
Molecular formula : CO2
(4) Ca (Valency 2) and O (Valency 2)
Ans. Step 1: Write the symbols of the constituent elements.
Ca O
Step 2: Write the valency below the respective elements.
Ca O
2 2
Step 3: Cross multiply the valencies.
Ca O
2 2
The formula : Ca2O2
Divide the formula by suitable number *2. The molecular
formula : CaO.
Q 10 Chemical composition of
some matter is given in the following table. Identify the main type of matter
from them.
|
Name of matter |
Chemical composition |
Main type of matter |
|
Sea water |
H2O + NaCl + MgCl2 + ... |
Mixture |
|
Distilled water |
H2O |
Compound |
|
Hydrogen gas filled in a balloon |
H2 |
Element |
|
The gas in LPG cylinder |
C4H10+C3H8 |
Mixture |
|
Baking soda |
NaHCO |
Compound |
|
Pure gold |
Au |
Element |
|
The gas in oxygen cylinder |
O2 |
Element |
|
Bronze |
Cu+Sn |
Mixture |
|
Diamond |
C |
Element |
|
Heated white powder of blue vitriol |
CuSO4 |
Compound |
|
Limestone |
CaCO3 |
Compound |
|
Dilute hydrochloric acid |
HCI+H2O |
Mixture |
