Science Textbook Solutions for Class 8 Science Chapter 6 - Composition of Matter

Important points to remember : 

  1. Matter  is classified into three types  ‘element’, ‘compound’ and ‘mixture’  by considering whether the smallest  particles  of matter  are similar  or different  and what are  they  made of. 
  2. All the smallest particles (atoms/ molecules)  in an element  or a compound are alike, however, the smallest particles in a mixture are of two or more types. 
  3. Various atoms in  the  molecules  of  compounds  are joined  by  chemical  bonds. The part of matter  having uniform composition  is called  phase. 
  4. When  all  the  components of a mixture form one phase, it is called  homogeneous mixture. 
  5. When the components of a mixture are distributed into two or more phases it is called a  heterogeneous mixture. 
  6. Solution :  A homogeneous mixture  of two or more  substances is called  solution. In the first beaker  in the  above activity  a homogeneous mixture of water and salt is formed.  It is called  a salt solution.  
  7. That component  of a solution  which  is present  in the  largest proportion  is called  solvent.  
  8. The other components which are in less proportion than the solvent are called  solutes. 

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

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

B. Hydrogen, hydrogen peroxide, carbon dioxide, water vapour.
Answer : Hydrogen is odd one out because it is an element and others are compound.

C. Milk, lemon juice, carbon, steel.
Answer : Carbon is odd one out because it is an element and others are mixture of various elements.

D. water, mercury, bromine, petrol.
Answer : Water is odd one out because it is universal solvent and rest are not universal solvent.

E. sugar, slat, baking soda, blue vitrol.
Answer : Baking soda is odd one out because it is a mixture of various elements and others are compound.

F. Hydrogen, sodium, potassium, carbon.
Answer : 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.
Answer : 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.
6CO2 + 6H2O → C6H12O6 + 6O26CO2 + 6H2O → C6H12O6 + 6O2

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

b. Gaseous element 
Answer : oxygen, nitrogen, hydrogen

c. Solid element 
Answer : sodium, carbon, aluminium

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

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

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

g. Complex compound 
Answer : chlorophyll, hemoglobin, cyanocobalamine

h. Inorganic compound 
Answer : limestone, rust, common salt

i. Metalloid 
Answer : silicon, germanium

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

k. Element with valency 2 
Answer : 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 :

  1. KCl :Potassium chloride K, ClK = 1, Cl = 1
  2. HBr : Hydrogen bromideK, Br K = 1, Br = 1
  3. MgBr2 : Magnesium bromide Mg, BrMg = 2, Br = 1
  4. K2O : Potassium oxide K, OK = 1, O = 2
  5. NaH : Sodium hydride Na, HNa = 1, H = 1
  6. CaCl2 : Calcium chloride Ca, ClCa = 2, Cl = 1
  7. CCl4 : Carbon tetrachloride C, ClC = 4, Cl = 1
  8. HI : Hydrogen iodide H, IH = 1, I = 1
  9. H2S : Hydrogen sulphide H, SH = 1, S = 2
  10. Na2S : Sodium sulphide Na, SNa = 1, S = 2
  11. FeS : Iron (II) Sulfide Fe, SF = 2, 

# Can you tell 
1. What are the various states of matter? 
Answer : There are three states of matter solid, liquid and gases.

2. What is the difference in ice, water and steam? 
Answer : Water as well steam ice is a type of waters and it is in the liquid and it has difference between liquid and also other states of message which is liquid molecules are more spread apart from that the solid molecules but less spread apart from that the other molecules such as the gas.

3. What are the smallest particles of matter called? 
Answer : Smallest particles are known as quarks and leptons that seem to be the fundamental building blocks.

4. What are the types of matter ?
Answer : In physics, a state of matter is one of the distinct forms in which matter can exist. Four states of matter are observable in everyday life: solid, liquid, gas, and plasma.

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