Which of the following statements is TRUE? I. The molar mass of CaCO3 is 100.1 g mol−1 II. 50 g of CaCO3 contains 9 ×1023 oxygen atoms. III. A 200 g sample of CaCO3 contains 2 moles of CaCO3 a I & II only b I & III c II & III only d I, II and III
Answers
Which of the following statements is (are) true ?
I. The molar mass of CaCO₃ is 100.1 g/mol
II. 50g of CaCO₃ contains 9 × 10²³ oxygen atoms.
III. A 200g sample of CaCO₃ contains 2 moles of CaCO₃.
some important date, we should use.
- atomic weight of Ca = 40.078 g/mol
- atomic weight of C = 12.0107 g/mol
- atomic weight of O = 15.997 g/mol
I. molar mass of CaCO₃ = atomic mass of Ca + atomic mass of C + 3 × atomic mass of O
= 40.078 + 12.0107 + 3 × 15.997
= 100.0797 ≈ 100.1 g/mol
Therefore option (1) is correct.
II. no of moles of CaCO₃ = mass of CaCO₃/molar mass of CaCO₃
= 50/100 = 0.5 mol
now no of CaCO₃ molecules = no of moles × Avogadro's number
= 0.5 × 6.023 × 10²³
= 3.0115 × 10²³ ≈ 3 × 10²³
∵ 1 molecule of CaCO₃ contains 3 , O atoms.
∴ no of O atoms = 3 × no of CaCO₃ molecules
= 3 × 3 × 10²³ = 9 × 10²³
Therefore option (2) is also correct.
III. no of moles of CaCO₃ = mass of CaCO₃/molar mass of CaCO₃
= (200g)/(100g/mol) = 2 mol
Therefore option (3) is also correct.