Chemistry – Chapter 1: Some Basic Concepts of Chemistry

 

Chemistry – Chapter 1: Some Basic Concepts of Chemistry

Competitive Exam Level – 6 Marks Questions

1. A compound contains 52.17% carbon, 13.04% hydrogen and 34.79% oxygen by mass. Determine its empirical formula. If its molar mass is 138 g mol⁻¹, determine its molecular formula.

2. A mixture contains (Na_2CO_3) and (NaHCO_3). On heating, 5.00 g of the mixture gives 0.560 g of (CO_2). Calculate the percentage composition of the mixture.

3. (10,g) of (CaCO_3) is treated with (100,mL) of (1,M) HCl. Determine the limiting reagent and calculate the volume of (CO_2) produced at STP.

4. A mixture of (CaCO_3) and (MgCO_3) weighing 10 g is heated completely. The mass of the residue obtained is 5.20 g. Calculate the percentage of (CaCO_3) and (MgCO_3) in the original mixture.

5. A gaseous hydrocarbon contains 85.7% carbon and 14.3% hydrogen by mass. If its vapour density is 21, determine its empirical and molecular formula.

6. For the reaction
   [
   2Al+3Cl_2\rightarrow2AlCl_3
   ]
   5.4 g Al is reacted with 14.2 g (Cl_2). Determine the limiting reagent and calculate the mass of (AlCl_3) formed.

7. A mixture contains 4.4 g (CO_2), 3.2 g (O_2), and 2.0 g (H_2). Calculate the total number of molecules and mole fraction of each gas.

8. A 2.0 g organic compound containing C, H and O produces 4.4 g (CO_2) and 1.8 g (H_2O) on complete combustion. If its molar mass is 60 g mol⁻¹, determine its molecular formula.

9. A 5.00 g sample of (KClO_3) is completely decomposed according to
   [
   2KClO_3\rightarrow2KCl+3O_2
   ]
   Calculate the number of (O_2) molecules produced and the volume of (O_2) at STP.

10. A 20 g impure sample of (CaCO_3) reacts with excess HCl and produces 3.36 L (CO_2) at STP. Calculate the percentage purity of (CaCO_3).

11. A solution is prepared by dissolving 5.85 g NaCl in 500 g water. Calculate its molality, mole fraction of NaCl and mole fraction of water.

12. A mixture of (Na_2CO_3) and (NaHCO_3) weighing 10 g is heated strongly. The final residue weighs 6.90 g. Determine the mass of each component in the original mixture.

13. (2.0,g) of (H_2) is reacted with (16,g) of (O_2):
    [
    2H_2+O_2\rightarrow2H_2O
    ]
    Determine the limiting reagent, theoretical yield of water and amount of excess reactant left.

14. A compound contains 40% C, 6.67% H and 53.33% O. If its vapour density is 90, determine its empirical formula and molecular formula.

15. 1 mole of (N_2) is mixed with 2 moles of (H_2) and allowed to react according to
    [
    N_2+3H_2\rightarrow2NH_3
    ]
    Determine the limiting reagent, moles of (NH_3) formed and moles of the excess reagent remaining.