50 short questions with answers covering some basic concepts of Chemistry for Class 11,
1. What is chemistry? The study of matter and its properties and how matter changes.
2. Define matter. Anything that has mass and occupies space.
3. What are the three states of matter? Solid, liquid, and gas.
4. Give two examples of a pure substance. Water, sugar.
5. What is a mixture? A substance comprising two or more components not chemically combined.
6. What are the two types of mixtures? Homogeneous and heterogeneous.
7. Define a homogeneous mixture. A mixture where the composition is uniform throughout.
8. Give an example of a homogeneous mixture. Salt solution.
9. Define a heterogeneous mixture. A mixture where the composition is not uniform throughout.
10. Give an example of a heterogeneous mixture. Sand and water.
11. What are the two types of pure substances? Elements and compounds.
12. Define an element. A substance that cannot be broken down into simpler substances by chemical means.
13. Give two examples of elements. Oxygen, nitrogen.
14. Define a compound. A substance formed when two or more elements are chemically combined in a fixed ratio.
15. Give two examples of compounds. Water (H2O), carbon dioxide (CO2).
16. What is a molecule? A group of two or more atoms held together by chemical bonds.
17. What is an atom? The smallest unit of an element that can exist.
18. What are physical properties? Properties that can be observed or measured without changing the identity of the substance.
19. Give two examples of physical properties. Color, density.
20. What are chemical properties? Properties that describe how a substance changes or reacts to form other substances.
21. Give two examples of chemical properties. Flammability, reactivity with acid.
22. What is meant by the law of definite proportions? A given compound always contains exactly the same proportion of elements by weight.
23. State the law of multiple proportions. If two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in the ratio of small whole numbers.
24. What is Avogadro's law? Equal volumes of all gases at the same temperature and pressure contain equal numbers of molecules.
25. What is a mole? The amount of a substance that contains as many elementary entities as there are atoms in exactly 12 grams of the carbon-12 isotope.
26. What is Avogadro's number? 6.022×1023 entities per mole.
27. What is molar mass? The mass of one mole of a substance, usually expressed in grams per mole (g/mol).
28. What is the relationship between molar mass and atomic mass? The molar mass of an element is numerically equal to its atomic mass expressed in atomic mass units (u).
29. What is the formula for calculating the number of moles? Number of moles (n) = Given mass / Molar mass (m/M).
30. What is molar volume of a gas at STP? 22.4 liters per mole.
31. What does STP stand for? Standard Temperature and Pressure (0°C or 273.15 K and 1 atm or 1 bar).
32. Define empirical formula. The simplest whole-number ratio of atoms of the constituent elements in a compound.
33. Define molecular formula. The actual number of atoms of each element in a molecule of the compound.
34. How is the molecular formula related to the empirical formula? Molecular formula = (Empirical formula)n, where n is a whole number.
35. What is stoichiometry? The quantitative relationship between reactants and products in a chemical reaction.
36. What is a limiting reactant? The reactant that is completely consumed in a reaction and determines the amount of product formed.
37. What is excess reactant? The reactant that is present in a greater amount than required for complete reaction with the limiting reactant.
38. What is theoretical yield? The maximum amount of product that can be formed from a given amount of reactants, assuming complete conversion.
39. What is actual yield? The amount of product that is actually obtained in a chemical reaction.
40. What is percentage yield? Percentage yield = (Actual yield / Theoretical yield) × 100%.
41. What is a solution? A homogeneous mixture of two or more substances.
42. What is a solute? The substance that is dissolved in a solution.
43. What is a solvent? The substance in which the solute is dissolved.
44. Define molarity. The number of moles of solute dissolved in one liter of solution (mol/L or M).
45. Define molality. The number of moles of solute dissolved in one kilogram of solvent (mol/kg or m).
46. What is the difference between molarity and molality? Molarity depends on the volume of the solution, while molality depends on the mass of the solvent.
47. What is a significant figure? Meaningful digits in a measured or calculated quantity.
48. State the rules for determining significant figures. (Implied: Non-zero digits are always significant, zeros between non-zero digits are significant, leading zeros are not significant, trailing zeros in a number containing a decimal point are significant, trailing zeros in a number not containing a decimal point may or may not be significant.)
49. What is precision in measurement? The closeness of various measurements for the same quantity.
50. What is accuracy in measurement? The agreement of a particular value to the true value of the result.
