(PART-2) Important Question of class 10 Science

                                                                                                                                            

                                                                                                                          

                                        Important Question

                                              Class 10

                                       Science(Part-2)

   

                                    [ For board Exam ]

                                                                                                                           

                          Unit 2

                                      Carbon and it's Compound

  

                                Periodic Classification of Element

                                                                                                              M.                        

General to specific Questions (3-5 marks)

1 

(A) Show the formation of Na2O( Sodium oxide) and MgO(Magnesium Oxide) by the transfer of electrons.

Answer:-

Formation of Na2O :  

The atomic number of sodium is 11 and it has only one valence electron. 

 Hence, electronic configuration of 11Na is 2, 8, 1. 

The atomic number of oxygen is 8 and it has 6 electrons in its valence shell.

  Hence, electronic configuration of 8O is 2, 6. 

 Sodium has a tendency to lose the valence electron and oxygen has a tendency to gain the electron lost by sodium. Since sodium can lose only one electron of the valence shell and oxygen atom needs two electrons to complete its octet in the valence shell, two atoms of sodium combine with one atom of oxygen. By losing valence electron, sodium is changed into Na+ and by gaining two electrons lost by two sodium atoms, oxygen atom is changed into an oxide anion, O2-. In this process, both the atoms, sodium and oxygen, obtain the stable electronic configuration of the noble gas neon. 

The oppositely charged sodium ion, Na+ and oxide ion, O2- are now held together by electrostatic forces of attraction or by ionic or electrovalent bond. Na2O is, therefore, an ionic or electrovalent compound.

 Formation of MgO: 

 It has two electrons in its outermost shell. So, the magnesium atom donates its 2 valence electrons and forms a stable magnesium ion, Mg2+ to attain the electronic arrangement of neon gas.

 It has six electrons in its valence shell. Therefore, it requires two more electrons to attain the stable electronic arrangement of neon gas. Thus, oxygen accepts two electrons donated by magnesium atom and forms a stable oxide ion, O2-.

 The oppositely changed magnesium ions, Mg2+ and oxide ions,O2-, are held together by a  strong force of electrostatic attraction to form Magnesium oxide compound Mg2+O2- or MgO. 

2

The electronic configuration of an element 'X' is 2,8,6 . To which group and period of the modern periodic table does 'X' belong. State their valency.

Answer:-

'X' belongs to 16th groups and 7th period.

Valency of 'X' is +2

3

What is homologous series? Write the name and draw the electron dot structure of second member of alkane.

Answer:-

A homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by CH​2 group. 

The name of the second member of the alkene series is Propene and its structure is..

4 

What happens when ethanol reacts with ethanoic acid in presence of  H2SO4.

Write the balanced equation and write the name of reaction?

Answer:-

The fruity smelling compounds belong to the class of esters (Ethyl acetate). The reaction of an ethanol (Alcohol) with an acid to from ester and water is called as esterification.

CH3COOH (Ethanoic acid) + C2H5OH( Ethanoic acid) ----------> CH.COOC2H5 (Ethyl Acetate)+ H2O 

Here, the ester formed is Ethyl Acetate. It is a sweet smelling ester. 

5

Write the difference between the Mandleev's periodic table and Modern periodic table.

Answer:-

6

Write three postulates of Dalton's atomic theory.

Answer:-

 Dalton's Atomic Theory

1) All matter is made of atoms. Atoms are indivisible and indestructible.

2) All atoms of a given element are identical in mass and properties

3) Compounds are formed by a combination of two or more different kinds of atoms.

4) A chemical reaction is a rearrangementof atom

___________________________________________________________________________________

5 Marks

7

Write the chemical formula and name of the compound which is the active ingredient of all alcoholic drinks. List its two uses. Write chemical equation and name of the product formed when this compound reacts with-

(I) Sodium metal

(II) Hot concentrated sulphuric acid.

Answer:-

Ethanol ( C2H5OH )

Uses in making of Syrup.

Use in making of Medicine.

(I) C2H5OH + Na --------> C2H5ONa + H2

(II) C2H5OH + H2SO4 ---------> C2H5SO4 + H20

8

Three elements X, Y, Z have atomic number 15 , 16 , 17  respectively

(A) State their position in periodic Table

(B) Write formula of compounds X when combined with Z

(C) Arrange them in increasing order of the atomic Radii.

Answer :-

The electronic configuration of the elements X, Y and Z can be written as: 

X-2,5 

Y-2,6 

Z-2,7 

(a) Since all the elements consists two valence shells, therefore all will belong to period 2nd Group to which

 X belongs = 10+5 = 15 Group to which Y belongs = 10 +6 = 16 Group to which Z belongs = 10+7 = 17

 (b)

When X combines with Z 
Valency of X=3 
Valency of Z =1 
Cross multiplying the valences
        
The compound formed is XZ3.

 (c) The elements can be arranged according to the decreasing order of atomic radii as follows: X>Y>Z. 

This is because size of the atom decreases when moving from left to right in a period.

 (c) When X combines with Z 
Valency of X=3 
Valency of Z =1 
Cross multiplying the valences
        
The compound formed is XZ3.

9

Write the limitation of Modern periodic table.

Answer:-

I) No fix position can be given to hydrogen.

II) No explanation of isotopes.

III) It was found a problem that atomic masses do not increase in the regular manner in going from one atom to another.

IV) In his law the properties of lithium and sodium were found to be save . Sodium is 8th element after lithium.

V) Similarly beryllium and magnesium resemble each other.

10

 

                                                                                                                                        

         

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