Class 8 Composition of matter exercise question answer general science
Class 8 general science chapter 6 question answer – Class 8 question answer Compound of matter – Compound of matter class 8 question answer maharshtra board
1. Choose the appropriate option and rewrite the following statements.
a. The
intermolecular force is …….. in the particles of solid.
i. minimum
ii. moderate
iii. maximum
iv. Indefinite
Ans: The intermolecular force is maximum in the particles of solid.
b.
Solids retain their volume even when external pressure is applied. This
property is called …….. .
i. plasticity
ii. incompressibility
iii. fluidity
iv. Elasticity
Ans: Solids retain their volume even when external pressure is applied. This property is called Elasticity.
C.
Matter is classified into the types mixture, compound and element, by applying
the criterion …….. .
i. states of matter
ii. phases of matters
iii. chemical composition of matter
iv. all of these
Ans: Matter is classified into the types mixture, compound and element, by applying the criterion chemical composition of matter .
d.
Matter that contain two or more constituent substances is called …….. .
i. mixture
ii. compound
iii. element
iv. Metalloid
Ans: Matter that contain two or more constituent substances is called mixture .
e. Milk is an example of type of matter called …….. .
i. solution
ii. homogeneous mixture
iii. heterogeneous mixture
iv. suspension
Ans: Milk is an example of type of matter called heterogeneous mixture .
f. Water, mercury and bromine are similar to each other, because three are …….. .
i. liquids
ii. compounds
iii. nonmetals
iv. elements
Ans: Water, mercury and bromine are similar to each other, because three are liquids.
g.
Valency of carbon is 4 and that of oxygen is 2. From this, we understand that
there are …… chemical bond/bonds between the carbon atom and one oxygen atom in the compound-carbon
dioxide.
i. 1
ii. 2
iii. 3
iv. 4
Ans: 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.
Class 8 general science question answer – General science question answer for 8th class – 8th class science all question answer
2. Identify the odd term out and explain.
Gold,
silver, copper, brass
Ans:
brass (Other are Element)
Hydrogen,
hydrogen peroxide, carbon dioxide, water vapour.
Ans:
Hydrogen (Other are compounds)
Milk,
lemon juice, carbon, steel.
Ans:
Carbon (other are mixtures)
Water,
mercury, bromine, petrol.
Ans:
Petrol ( other are inorganic compounds)
Sugar,
salt, baking soda, blue vitriol.
Ans:
Sugar (Other are inorganic compound)
Hydrogen,
sodium, potassium, carbon.
Ans:
Carbon ( Other are monovalent elements)
3.
Answer the following question.
a. 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:
Carbon dioxide, water, glucose, and chlorophyll are compounds.
Types: Organic compounds : Glucose
Inorganic compounds: Carbon dioxide and water
Complex
compounds: Chlorophyll.
b. 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.
c. 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 % , Mediterranean 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 salt in water) do not combine chemically.
2)Their constituents are present in any proportion by weight.
3)The
constituents of a mixture can be separated by physical process.
4. Give two examples each
a. Liquid element
Ans:
- Mercury (Hg)
- Bromine(Br2)
b. Gaseous element
Ans:
1) Hydrogen (H2)
2) Oxygen(O2)
c. Solid element
Ans:
1) Iron (Fe)
2) Copper(Cu)
d. Homogeneous mixture
Ans:
- sea water
- blue virtriol dissolved in water
e. Colloid
Ans:
1) Milk
2) blood
f. Organic compound
Ans:
1) Glucose
2) urea
g. Complex compound
Ans:
1) chlorophyll
2) Haemoglobin
h. Inorganic compound
Ans:
1) soda
2) rust
i. Metalloid
Ans:
1) silicon
2) arsenic
j. Element with valency 1
Ans:
1) Sodium (Na)
2) Potassium (K)
k. Element with valency 2
Ans:
1) Magnesium(mg)
2) Calcium (Ca)
5. Write the names and symbols of the constituent elements and identify their valencies from the molecular formulae given below.
KCl, HBr, MgBr2, K2 O, NaH, CaCl2, CCl4, HI, H2S, Na2S, FeS, BaCl2
Ans:
|
Sr. No. |
Molecular formula |
Constituent element/ Name symbol |
valancy |
|
1. |
KCl |
Potassium (K) Chlorine
(Cl) |
1 1 |
|
2. |
HBr |
Hydrogen (H) Bromine (Br) |
11 |
|
3. |
MgBr2 |
Magnesium Bromine (Br) |
21 |
|
4. |
K2O |
Potassium(K) Oxygen(O) |
12 |
|
5. |
NaH |
Sodium (Na) Hydrogen
(H) |
11 |
|
6. |
CaCl2 |
Calcium Chlorine(Cl) |
21 |
|
7. |
CCl4 |
Carbon(C) Chlorine(Cl) |
41 |
|
8. |
HI |
Hydrogen(H) Iodine (I) |
11 |
|
9. |
H2S |
Hydrogen(H) Sulphur
(S) |
12 |
|
10. |
Na2S |
Sodium (Na) Sulphur (S) |
12 |
|
11. |
FeS |
Iron(Fe) Sulphur(S) |
22 |
|
12. |
BaCl2 |
Barium (Ba) Chlorine(Cl) |
21 |
6. Chemical composition of some matter is given in the following table. Identify the main type of matter from their.
Name of
matter Chemical composition Main type of matter
Sea
water H2O + NaCl + MgCl2 +… Mixture
Distilled
water H2O Compound
Hydrogen
gas filled in a ballon H2 Element
The gas
in LPG cylinder C4H10 + C3H8 Mixture
Baking
soda NaHCO3 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
Lime
stone CaCO3 Compound
Dilute
hydrochloric acid HCl + H2O mixture
8th science guide answer – 8th standard general science question answer – Class 8 general science question answer – General science question answer for 8th class
7. Write scientific reason.
a. 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 .
b. Constituent substances of a colloid cannot be separated by ordinary 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 .
c. 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 .
d. A solid matter has the properties of definite shape and volume.
Ans:
1. The forces among the constituent are called particles (atom/molecules) 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 .
8. Deduce the molecular formulae of the compound obtained from the following pairs of elements by the cross multiplication method.
a. C (Valency 4) & Cl (Valency1)
Ans:
Step 1.: write the symbols of the constituent element
C Cl
Step 2: write the valency below the respective elements.
C Cl
4 1
Step3: cross multiply the valencies.
C×1 Cl×4
The
molecular formula: CCl4
b. N (Valency 3) & H (Valency 1)
Ans:
Step 1.: write the symbols of the constituent element.
N H
Step 2: write the valency below the respective elements.
N H
3 1
Step3: cross multiply the valencies.
N×1 H×3
The
molecular formula: NH3
c. C (Valency 4) & O (Valency 2)
Ans:
Step 1.: write the symbols of the constituent element.
C O
Step 2: write the valency below the respective elements.
C O
4 2
Step3: cross multiply the valencies.
C×2 O×4
The molecular formula: C2O4
Final molecular formula obtained by dividing by 2
The molecular formula : CO2
d. Ca (Valency 2) & O (Valency 2
Ans:
Step 1.: write the symbols of the constituent element.
Ca O
Step 2: write the valency below the respective elements.
Ca O
2 2
Step3: cross multiply the valencies.
Ca ×2 O ×2
The molecular formula: Ca2O2
Divide the formula by suitable number ‘2’.
The
molecular formula : CaO.
