Some Basic Concepts of Chemistry

JEE-Mains/Advance

1. 3 g of hydrocarbon on combustion with 11.2 g of oxygen produce 8,8 g of CO₂ and 5.4 g of H₂O. The data illustrate the law of: [conservation of mass]
2. An unknown element forms an oxide. What will be the equivalent mass of the element if the oxygen content is 20% by mass: [32]
3. A metal M of equivalent mass E forms an oxide of molecular formula M_xO_y– The atomic mass of the metal is given by the correct equation: [2E(y/ x)]
4. A chloride of an element contains 49.5% chlorine. The specific heat of the element is 0.056. Calculate the equivalent mass, valency and atomic mass of the element. (Ans: 108.63).
5. Potassium chromate is isomorphous to potassium sulphate (K₂SO₄) and is found to contain 26.78% chromium. Calculate the atomic mass of chromium (K = 39.10). (Ans: 52)
6. The oxide of an element contains 32.33 percent of the element and the vapour density of its chloride is 79. Calculate the atomic mass of the element. (Ans: 15.28)
7. It is found that 16.5 g of metal combine with oxygen to form 35.60 g of metal oxide. Calculate the percentage of metal and oxygen in the compound. (Ans: M=46.3; O= 53.4)
8. A carbon compound containing only carbon and oxygen has an approximate molecular mass of 290. On analysis, it is found to contain 50% by mass of each element. What is the molecular formula of the compound? (Ans: C₁₂O₉).
9. A compound contains 34.8% oxygen, 52.2% carbon and 13.0% hydrogen. What is the empirical formula mass of the compound? [Ans: C₂H₆O; 46]
10. A compound of C, H and N contains these elements in the ratio 9: 1: 3.5. Calculate the empirical formula. If its molecular mass is 108, what is the molecular formula? [ C₆H₈N₂]
11. A compound has an empirical formula C₂H₄O. An independent analysis gave a value of 132.16 for its molecular mass. What is the correct molecular formula? [C₆H₁₂O₃]
12. An organic compound containing C and H has 92.30% carbon. What is the empirical formula?
13. Two oxides of a metal contain 50% and 40% of metal M respectively. If the formula of first oxide is MO, the formula of 2nd oxide will be: [Ans: M₂O₃]
14. 0.44 g of a hydrocarbon on complete combustion with oxygen gave 1.8 g water and 0.88 g carbon dioxide. Show that these results are in accordance with the law of conservation of mass.
15. An alloy of iron (54.7%), nickel (45%) and manganese (0.3%) has a density of 8.17 g/cm³. How many iron atoms are there in a block of alloy measuring 10cm x 20cm x 15 cm?
16. The equivalent mass of an element is 4. Its chloride has vapour density 59.25. Then the valency of the element is: [ Ans: 3]
17. A mixture of hydrogen and oxygen contains 20% by mass of hydrogen. What is the total number of molecules present per gram of the mixture? [ 0.1; 0.025]
18. How many electrons ate present in 18 mL of water? [10N_A]
19. What mass of potassium chlorate (KClO₃) on heating gives 1.491 g of potassium chloride (KCl) and 0.672 litres of oxygen at NTP? [2.451].
20. A hydrated chloride of metal contains 18.26% metal and 32.42% chloride ion by mass. The specific heat of metal is 0.16. What is hydrated chloride? [Ans. CaCl₂·6H₂O]
21. Calculate the molality of a solution containing 20.7 g potassium carbonate dissolved in 500 ml of solution (assume density of solution = 1g/ml) [Ans: 0.313]