Atoms and Molecules Worksheet-7

Atoms and Molecules Worksheet-7

11. Calculate the number of Mg atoms in 0.024 g of Mg.

12. Write the names of the compounds represented by the following formulae :

(i) Al₂(SO₄)₃               (ii) CaCl₂            (iii) K₂SO₄

(iv) KNO₃                    (v) CaCO₃.

13. Calculate the number of moles of 52 g of He.

14. Calculate the number of particles in 0.1 mole of carbon atoms.

15. If one mole of carbon weighs 12 grams, what is the mass (in gram) of one atom of carbon?

16. What are polyatomic ions? Given examples.

17. Given the names of the elements present in Quick lime.

(a) Quick lime                     (b) Hydrogen bromide

(c) Baking powder              (d) Potassium sulphate.

18. Given the names of the elements present in Quick lime.

19. Given the names of the elements present in Baking powder.

20. Given the names of the elements present in Potassium sulphate.

Answer:

11. 24 g of Magnesium contains 6.022 × 10²³ atoms

∴ 0.024 g of Mg = 6.022 × 10²⁰ atoms

12. (i) Aluminium sulphate

(ii) Calcium chloride

(iii) Potassium sulphate

(iv) Potassium nitrate

(v) Calcium carbonate.

13. (i) 52 g of He

14. 0.1 mole of carbon atoms

No. of particles (atoms) = No. of moles (n) × Avogadro’s no. (No)

= (0.1) × (6.022 × 10²³) = 6.022 × 10²² atoms.

15. 1 Gram molecular mass of carbon = 12 g

 6.022 × 10²³ atoms of carbon have mass = 12 g

16. Polyatomic ions are the group of atoms which carry either positive charge (cations) or negative charge (anions).

For example-

(i)     Carbonate (CO₃)^2–ion

(ii)    Nitrate ion (NO₃^–)   

(iii)   Ammonium ion (NH₄)⁺

(iv)   Phosphate ion (PO₄)^3–

17. The names of elemrnts present can be given only if the chemical formula of the compound is known. For example,

(a) Quick lime : It is the commercial name of the compound. Its chemical name is calcium oxide and the chemical formula is CaO.

Elements present : calcium (Ca) : oxygen (O)

(b) Hydrogen bromide : The chemical formula of the compound is HBr

Elements present : hydrogen (H); bromine (Br)

(c) Baking powder : It is the commercial name of the compound. Its chemical name is sodium hydrogen carbonate and the chemical formula is NaHCO₃

Elements present: sodium (Na), hydrogen (H), carbon (C), oxygen (O).

(d) Potassium sulphate : The chemical formula of the compound is K₂SO₄

Elements present: potassium (K), sulphur (S), oxygen (O).

18. (a) Quick lime : It is the commercial name of calcium oxide and its chemical formula is CaO.

Elements present : calcium (Ca) : oxygen (O)

19. Baking powder : It is the commercial name of Sodium hydrogen carbonate and its chemical formula is NaHCO₃

Elements present: sodium (Na), hydrogen (H), carbon (C), oxygen (O).

20. Potassium sulphate :

The chemical formula of the compound is K₂SO₄

Elements present: potassium (K), sulphur (S), oxygen (O).