Ncert Solutions Chemistry Class 11th

3.1. The basic theme of organisation of elements in the periodic table is to simplify, systematize and classify the elements based on their similarities in properties. This arrangement makes it easier for us to group the elements and makes it less confusing to present the periodic table.

1.51. In 1808, Dalton published 'A New System of Chemical Philosophy', in which he proposed the following:

1. Matter consists of indivisible atoms.

2. All atoms of a given element have identical properties, including identical mass. Atoms of different elements differ in mass.

3. Compounds are form

1.50. Carbon-12 isotope is the most abundant isotope of carbon and has been chosen as the standard. Since C-12 is used as the standard atom, one atomic mass unit is defined as one-twelfth of the mass of one carbon – 12 atoms. This is because it has an equal number of protons and neutrons (6) an

1.49. The empirical mass of ethene is half of its molecular mass. The empirical formula represents the simplest whole-number ratio of various atoms present in a compound.

Molecular Formula = n * Empirical formula

Empirical formula of Ethene = C₂H₄

Empirical Formula Mass = 14 amu= ½ Molecular Mass

1.48. 

1.47. These rules for determining the number of significant figures are stated below:

(1) All non-zero digits are significant. For example, in 285 cm, there are three significant figures and in 0.25 mL, there are two significant figures.

(2) Zeros preceding to first non-zero digit are not significan

1.46.  (c) both a and b

1.45.  (d) 36 g of water

CH₄ + 2O₂ → CO₂ + 2H₂O

1 mol of CH₄ reacts with 1 mol O₂ of to produce 2 moles of H₂O

It means that 16g of CH₄ reacts with oxygen to produce (2x18)= 36g of water

1.44.  (b) Candela

1.43. (c) The mass of 1 mole of C-12 atoms = 12 g

1 mole of C- atoms = 6.022 * 10²³ atoms

The mass of 1 atom of C-12 = 12 / (6.022 * 10²³)

= 1.99 * 10^–23 g