Friday, October 19, 2012

IX(9th)Chemistry Ch 03:Atoms and Molecules Solved Questions

1. Avogadro’s number represents the number of atoms in
(a) 12g of C12                                       (b) 320g of sulphur      
(c) 32g of oxygen                                (d) 12.7g of iodine

2. The number of moles of carbon dioxide which contain 8 g of oxygen is
(a) 0.5 mol                                           (b) 0.20 mol                              
(c) 0.40 mol                                         (d) 0.25 mol

(3) The total no of ions present in 111 g of cacl2 is
(a) One mole                                        (b) Two mole              
(c) Three mole                                     (d) Four moles

(4) Which of the following weighs the most ?
(a) one g-atom of nitrogen                   (b) One mole of water
(c) One mole of sodium                                   (d) One molecule of H2So4

(5) 5.0 litre of 0.4 M H2SO4 Contains-
(a) 2.0 Mole Of H2So4                                    (b) 0.4 mole H2So4
(c) 5.0 mole H2So4                             (d) 2.0 moles H2O

Ans: (1) a  (2) d (3) c (4) c (5) a

1. Find the ratio by mass of the combining elements in the compound – C2H5OH.
Ans: C = 2x12=24; H = 6x1=6 ; O= 1x16=16
C : H:O =24:6:16 = 12:3:8

2. Give the formula of the compound formed by the elements calcium and fluorine.
Ans:  Ca+2 F-1          CaF2

3. What is the acid radical present in sodium peroxide?
Ans: The acid radical present in sodium peroxide (Na202) is peroxide radical (02-2)

4. Carbon and silicon have the same valency. What is the formula of sodium silicate?
Valency of silicon and carbon is  4.
The formula of sodium silicate is Na+1  SiO3 -2  = Na2 SiO3

5. What is the ratio by number of atoms in mercurous chloride?
Ans: Formula of mercurous chloride is HgCI. Ratio of the atoms of Hg and CI in HgCI is 1: 1.

6. Name the element whose Latin name is Stibium.
Ans: Antimony (Latin:  stibium); Mercury (Latin: hydragyrum); Gold (Latin: aurum); Lead (Latin: plumbum).

7. What is the valency of a sulphide ion?
Ans: Valency of sulphide ion  So 4 -2 is —2 eg.H2SO4

8. How many atoms of oxygen are present in 50g of CaCO3?
Molecular mass  of CaCO3 = 40 + 12 + 3 X 16=100g
Atoms of oxygen are present  in 100 g of CaCO  
= 3 x 6.022 x 1023 atoms
Atoms of oxygen are present  in 50 g of CaCO  = {( 3 x 6.022 x 1023) /100} x 50 atoms
                                                                         = 9.033 X 1023

9. How many molecules are present in 1 ml of water?
Molecular mass of H2O  =18gm  also, Mass of 1 mole of water=  1gm
18gm of water contain = 6.022 x 1023 molecules
1gm of water contain = (6.022 x 1023 )/18molecules = 3.34 x 1022

10. What is the unit of measurement of atomic radius?
Ans: picometers (pm) or Angstroms (Å)

1 comment:

mateentmg said...

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