IX CLASS ATOMIC STRUCTURE ASSIGNMENT -1

1. All sample of carbon dioxide contains carbon and oxygen in the mass ratio of 3:8.This is in agreement of law of

(a)conservation of mass                   (b) constant proportions

(c) multiple  proportion                     (d) gaseous volume

2. The indivisibility  of atom was proposed by

(a) Rutherford                                     (b) Dalton

(c) Bohr                                                (d) Einstein

3. The value of the Avogadro constant  is

(a) 6.022 x 10^{– 22}                   (b) 6.022 x 10^{– 24}

(c) 6.022 x 10 ^{– 23}                  (d) None of these 

4. The volume of 1 mole of gas at standard temperature and pressure is

(a) 11.2 litres                                        (b) 22.4litres

(c) 100 litres                                         (d) none of these

5. The atomic mass of sodium is 23. The number of moles in 46 g of sodium is

(1) 1                                                      (b) 2       

(c) 2.3                                                   (d) 4.6

6. Empirical formula of a compound of molecular mass 120 is CH₂O. The molecular formula of the compound is

(a) CH₄0₂                                              (b) C₄H₈0₄

(c)C₃H₆ O₃                                            (d) none of these

7. Which of the following is a tetra atomic molecule.

(a) O₂                                                    (b) O₃     

(c) NO₂                                                 (d) SO₃

8. The number of atoms present in a molecule of a substance is called

(a) molecularity                                   (b) atomicity

(l)  valency                                          (d) reactivity

9. The valency of nitrogen in ammonia (NH₃) is

(a)  2                                                     (b)  0      

(c)  3                                                     (d)  4

10. The molecular formula of ethanoic acid is C₂H₄O₂ . Its empirical formula is

(a) C₄H₈O₂                                            (b) CH₂O

(c) CHO                                                (d) CHO₂

Answers.

1	b	6	b
2	b	7	b
3	c	8	b
4	b	9	c
5	b	10	b

Mark the statements True (T) or False (F).

1.        A molecule is made up of atoms.

2.        Atoms of different elements have the same mass.

3.        The symbol of silver is S. 

4.        1 amu =  1/12 th  the mass of one C–12 atom.

5.        The molecules of different substances have the same mass.

6.        All elements having valency 2 are called divalent.

7.        The formula of sodium carbonate is Na₂CO₃.

8.        Noble gas molecules are diatomic.

9.        The molecular formula of a compound is determined by the valency of the elements present in the compound.

Answer the following in one word or a maximum of one sentence.

1.Who was the first to propose the concept of compound atom?

2.What is meant by the gram–atomic mass of an element?

3.The atomic masses of sodium and chlorine are 23 and 35.5 respectively. What is the formula mass of       sodium chloride?

4.The atomic mass of Ca is 40 and the molecular mass of CaCO₃ is 100. What  is the percentage of Ca        in CaCO₃ ?

5.What is a symbol?

6.What is an atom?

7.Write the formula of calcium nitrate.

8.The molecular formula of sulphur is S. What do you understand by this?

9.Define valency of an element.

10.What is an ion?

11.Write the chemical formula of the following:    (a) Calcium chloride (b) Aluminium nitrate

12.Give the names of elements present in ammonium chloride.

13.What is the mass of 1 mole of oxygen atoms?

14.Convert into mole:

      (a) 28 g of nitrogen atoms (b) 20 g of carbon dioxide