CLASS 9 WORKSHEET-ATOMS AND MOLECULES

1. calculate the formula mass of sodium carbonate.Na₂CO₃.10H₂O.-Ans 286u

2. Give three significance of a mole.

Ans One mole represents 6.022 x10²³ entities of a substance

       One mole of an element contains 6.022 x10²³   atoms of an element

        One mole of a substance represents one gram formula mass of the substance

3.calculate the molar mass of the following substances

(i) Ethyne  C₂H₂      12x2+1x2=26g mol^-1

 (ii) nitric acid   1+14+16x3= 63gmol^-1

_{4.calculate the number of moles present in
(i) 3.011x10}²³ _number of oxygen atoms            Ans 0.5mol

(ii) 60g of Calcium                                     Ans1.5 mol

5.Calculate the molecular masses of  (i)CH₃OH(ii) NH₃   Ans 32u  , 17 u

6. Write the postulates of Dalton atomic Theory. Explain its drawbacks

7. Write the cations and anions present in the following compounds

(i) CH₃COONa  (ii) NH₄NO₃  (iii) H ₂  (iv) NaCl

8.Write the formula of the compounds formed by the following ions

(i) Mg⁺² and S^-2   (ii) Cu⁺² and OH^-

9.How many (i) atoms (ii) molecules(iii) oxygen atoms are there in 0.5 mol of water? Ans (i) 3.011x10²³ (ii)6.022x10²³ (iii) 3.011x10²³

10 calculate the mass percent of each element of sodium in one mole of it.

Ans Mass % of Na=39.32%      Mass % of Cl = 60.68