Class 8 chapter 6. Composition of matter Text book Solution

6. Composition of matter

1. Choose the appropriate option and rewrite the following statements.

a. The intermolecular force is maximum in the particles of solid.

i. minimum ii. moderate iii. maximum iv. indefinite

b. Solids retain their volume even when external pressure is applied. This property is called incompressibility .

i. plasticity ii. incompressibility iii. fluidity iv. elasticity

C. Matter is classified into the types mixture, compound and element, by applying the criterion states of matter.

i. states of matter ii. phases of matters

iii. chemical composition of matter iv. all of these

d. Matter that contain two or more constituent substances is called compound .

i. mixture ii. compound iii. element iv. metalloid

e. Milk is an example of type of matter called homogeneous mixture

i. solution ii. homogeneous mixture iii. heterogeneous mixture iv. suspension

f. Water, mercury and bromine are similar to each other, because three are ........ .

i. liquids ii. compounds iii. nonmetals iv. elements

g. 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. i. 1 ii. 2 iii. 3 iv. 4

2. Identify the odd term out and explain.

a. Gold, silver, copper, brass

Ans : .Brass is odd one out because it is an alloy and gold, silver, copper are element.

b. Hydrogen, hydrogen peroxide, carbon dioxide, water vapour.

Ans: Hydrogen is odd one out because it is an element and others are compound

c. Milk, lemon juice, carbon, steel.

Ans: .Carbon is odd one out because it is an element and others are mixture of various elements.

d. Water, mercury, bromine, petrol.

Ans: Water is odd one out because it is universal solvent and rest are not universal solvent.

e. Sugar, salt, baking soda, blue vitriol.

Ans: Baking soda is odd one out because it is a mixture of various elements and others are compound.

f. Hydrogen, sodium, potassium, carbon.

Ans: Carbon is odd one out because it has 4 valence electrons and others have 1 valence electron.

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 is a chemical process through which plants, some bacteria and algae, produce glucose and oxygen from carbon dioxide and water, using only light as a source of energy, which is absorbed by chlorophyll.
$6 {CO}_{2} + 6 H_{2} O \to C_{6} H_{12} O_{6} + 6 O_{2}$
Four substances in this process are as follows:
>Carbon dioxide = organic compound
>Water = organic compound
>Glucose = organic compound
>Chlorophyll = organo-metallic compound or complex compound

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: Characteristics of mixtures from above information are:
1.Constituent substances of a mixture are two or more elements or compounds.
2.The proportion of constituent substances in a mixture can be variable.
3.The properties of constituent substances are retained in the mixture.

4. Give two examples each

a. Liquid element : mercury, bromine

b. Gaseous element : oxygen, nitrogen, hydrogen

c. Solid element: sodium, carbon, aluminium

d. Homogeneous mixture: sugar in water, corn oil, blood plasma

e. Colloid: milk, butter, gelatin, jelly, muddy water

f. Organic compound : proteins, glucose, urea, carbohydrates

g. Complex compound: chlorophyll, hemoglobin, cyanocobalamine

h. Inorganic compound : limestone, rust, common salt

i. Metalloid: silicon, germanium

j. Element with valency 1: sodium, potassium, chlorine

k. Element with valency 2: magnesium, calcium

5. Write the names and symbols of the constituent elements and identify their valencies from the molecular formulae given below. KCl, HBr, MgBr2, K2O, NaH, CaCl2, CCl4, HI, H2S, Na2S, FeS, BaCl2

Compounds	Name of compounds	Symbol of constituent elements	Valency of constituent elements
KCl	Potassium chloride	K, Cl	K = 1, Cl = 1
HBr	Hydrogen bromide	K, Br	K = 1, Br = 1
MgBr₂	Magnesium bromide	Mg, Br	Mg = 2, Br = 1
K₂O	Potassium oxide	K, O	K = 1, O = 2
NaH	Sodium hydride	Na, H	Na = 1, H = 1
CaCl₂	Calcium chloride	Ca, Cl	Ca = 2, Cl = 1
CCl₄	Carbon tetrachloride	C, Cl	C = 4, Cl = 1
HI	Hydrogen iodide	H, I	H = 1, I = 1
H₂S	Hydrogen sulphide	H, S	H = 1, S = 2
Na₂S	Sodium sulphide	Na_,S	Na = 1_,S = 2
FeS	Iron (II) Sulfide	Fe, S	F = 2, S = 2
BaCl₂	Barium chloride	Ba, Cl	B = 2, Cl = 1

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(molecule)
The gas in LPG cylinder	C4H10 + C3H8	mixture
Baking soda	NaHCO3	mixture
Pure gold	Au	element
The gas in oxygen cylinder	O2	element(molecule)
Bronze	Cu + Sn	mixture
Diamond	C	element
Heated white powder of blue vitriol	CuSO4	compound
Lime stone	CaCO3	compound
Dilute hydrochloric acid	HCl + H2O	compound

7. Write scientific reason.

a. Hydrogen is combustible, oxygen helps combustion, but water helps to extinguish fire.

Ans: Water is a compound of hydrogen and oxygen.

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^-5m.

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: .Lemon sherbat has sweet, sour and salty taste and it can be poured in a glass because sour taste indicates presence of an acid and if acid is poured in a vessel made up of metal, then acid reacts with metal and makes it poisonous in nature.So we prefer to take vessel made up of glass material.

d. A solid matter has the properties of definite shape and volume.

Ans: A solid matter has the properties of definite shape and volume because of the following reasons:
1.Intermolecular force of attraction between the particles of matter is very strong.
2.Internuclear space between the particles of matter is negligible.
3.Particles of matter are very close to each other that they only vibrate at their fixed position.

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)

Step 1 : Write the symbols of the radicals.
   C Cl
Step 2 : Write the valency below the respective radical.
   C    Cl
4    1
Step 3 : Cross-multiply symbols of radicals with their respective valency.

Step 4 : Write down the chemical formula of the compound.

CCl₄

b. N (Valency 3) & H (Valency 1)

Step 1 : Write the symbols of the radicals.
   N H
Step 2 : Write the valency below the respective radical.
   N    H
3    1
Step 3 : Cross-multiply symbols of radicals with their respective valency.

Step 4 : Write down the chemical formula of the compound.

NH₃

C (Valency 4) & O (Valency 2)

Step 1 : Write the symbols of the radicals.
   C O
Step 2 : Write the valency below the respective radical.
   C    O
4    2
Step 3 : Cross-multiply symbols of radicals with their respective valency.

Step 4 : Write down the chemical formula of the compound.

CO₂

d. Ca (Valency 2) & O (Valency 2)

Step 1 : Write the symbols of the radicals.
   Ca    O
Step 2 : Write the valency below the respective radical.
   Ca O
2    2
Step 3 : Cross-multiply symbols of radicals with their respective valency.

Step 4 : Write down the chemical formula of the compound.

CaO

Class 8 chapter 6. Composition of matter Text book Solution

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