STD 8 SCIENCE 6. Composition of Matter

Question 1:

Choose the appropriate option and rewrite the following statements.

A. The intermolecular force is _______ in the paricles of solid.

i. Minimum ii. Moderate iii.maximum iv.indefinite.

B. Solids retain their voume even when external pressure is applied. This property is called__________

i. plasticity ii. Incompressibility iii. fluidity iv. 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 compositions of matter iv all of these

D. Matter that contain two or more constituent substances is called__________

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

E. Milk is an example of type of matter called __________

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

F. Water, mercury and bromine are similar o 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 _______ chemical bond/bonds between the carbon atom and one oxygen atom in the compound-carbon dioxide.

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

Answer 1:

A. The intermolecular force is maximum in the paricles of solid.

i. Minimum ii. Moderate iii.maximum iv.indefinite.

B. Solids retain their voume 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 criterionstates of matter.

i. states of matter ii Phases of matters iii chemical compositions 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 liquids.

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

Question 2:

Identify the odd term out and explain

A. Gold, silver, copper, brass

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

C.Milk, lemon juice, carbon, steel.

D.water, mercury, bromine, petrol.

E.sugar, slat, baking soda, blue vitrol.

F.Hydrogen, sodium, potassium, carbon.

Answer 2:

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

b.Hydrogen is odd one out because it is an element and others are compound.

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

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

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

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

Question 3:

Answer the following questions.

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.

B. In one sample of brass, the following ingredients were found : copper (70%) and zinc (30%). Identify the solvent, solute and solution from these.

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 mixture from the above information.

Answer 3:

a.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:

1.Carbon dioxide = organic compound

2.Water = organic compound

3.Glucose = organic compound

4.Chlorophyll = organo-metallic compound or complex compound

b.Brass is an alloy made primarily of copper, usually with zinc.Brass as a solid solution consisting of zinc and other metals as solute dissolved in copper taken as solvent. So that, the brass meets all the criteria of a solution.

c.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.

Question 4:

Give two examples each

A. Liquid element

B. Gaseous element

C. Solid element

D.Homogeneous mixture

E.Colloid

F.Organic compound

G.Complex compound

H.Inorganic compound

I.Metalloid

J.Element with valency 1

K.Element with valency 2

Answer 4:

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 = mayonnaise, 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

Question 5:

Write the names and symbols of the constituent eleements and identify their valencies from the molecular formulae given below.

KCl, HBr, MgBr2, K2O, NaH, CaCl2, CCl4, HI, H2S, Na2S, FeS, BaCl2

Answer 5:

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

Question 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	$H_{2} O + N a C l + M g C l_{2}$
Distilled water	$H_{2} O$
Hydrogen gas filled in a ballon	$H_{2}$
The gas in LPG cylinder	$C_{4} H_{10} + C_{3} H_{8}$
Baking soda	$N a H C O_{3}$
Pure gold	$A u$
The gas in oxygen cylinder	O2
Bronze	Cu + Sn
Diamond	C
Heated white powder of blue vitroi	CuSO4
Lime stone	CaCO3
Dilute hydrochloric acid	HCL+ H2O

Answer 6:

Name of matter	Chemical composition	Main type of matter
Sea water	$H_{2} O + N a C l + M g C l_{2}$	mixture
Distilled water	$H_{2} O$	compound
Hydrogen gas filled in a ballon	$H_{2}$	element(molecule)
The gas in LPG cylinder	$C_{4} H_{10} + C_{3} H_{8}$	mixture
Baking soda	$N a H C O_{3}$	mixture
Pure gold	$A u$	element
The gas in oxygen cylinder	$C_{4} H_{10} + C_{3} H_{8}$	element(molecule)
Bronze	Cu + Sn	mixture
Diamond	$C$	element(allotrope)
Heated white powder of blue vitroi	${CuSO}_{4}$	compound
Lime stone	$C a C O_{3}$	compound
Dilute hydrochloric acid	$HCL + H_{2} O$	compound

Question 7:

Write scientific reason.

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

B. Constituent substances of a colloid cannot be separated by ordinary filtration.

C. Lemon sherbat has sweet, sour and salty taste and it can be poured in a glass.

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

Answer 7:

a.Water is made up of two elements, that's hydrogen and oxygen. Hydrogen is flammable, but oxygen is not. Flammability is the ability of a combustible material with an adequate supply of oxygen (or another oxidiser) to sustain enough heat energy to keep a fire going after it has been ignited. Though water is made up of two atoms of hydrogen and one atom of oxygen by forming an ionic compound, it does not possess the characteristics of them because a compound does not have the properties of its constituent elements. Therefore, water has its own properties, which helps to extinguish fire.

b.Constituent substances of a colloid cannot be separated by ordinary filtration because the size of the particles in a colloids(or colloidal solution) is bigger than those in a true solution but smaller than those in suspension.It is in between 1nm to 100nm in diameter. The size of ordinary filter paper is more than 100nm due to which colloidal particles are passed through the pores of a filter paper. Due to which, we prefer to use ultrafilter paper so that, filteration of colloidal particles take place easily.

c.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 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.

Question 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 (Valency 1)

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

C. C (Valency 4) & O (Valency 2)

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

Answer 8:

a. C (Valency 4) & Cl (Valency 1) :

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. 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

STD 8 SCIENCE 6. Composition of Matter

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