Atoms and Molecules

Atoms and Molecules Worksheet-4

1. One ‘u’ stands for :

A. An atom of carbon (C-12)

B. 1/12^th of mass of carbon atom (C-12)

C. 1/12^th Of hydrogen atom.

D. One atom of all the elements.

2. How many times an atom of sulphur is heavier then an atom of carbon?

A. 32 times                                     B. 12 times

Atoms and Molecules Worksheet-5

11. The value of Avogadro’s  constant is :

A. 6.0 × 10²⁴                                  B. 6.022 × 10²²

C. 6.022 × 10²³                             D. 6.022 × 10^–23

12. The atomic mass of calcium is 40 u. The number of calcium atoms in 0.4 u of calcium is :

A. 6.022 × 10¹⁰                             B. 6.022 × 10²²

Atoms and Molecules Worksheet-6

1. In a reaction 4.0 g of sodium carbonate were reacted with 10 g of hydrochloric acid. The product was a mixture of 2.5 g of carbon dioxide and 11.5 g of sodium chloride solution. Is this data in agreement with the law of conservation of mass?

2. If 6.3 g of sodium bicarbonate are added to 15.0 g of ethanoic acid (or acetic acid) solution, the residue left is found to weigh 18.0 g. what mass of CO₂ is released in the reaction?

3. The percentage of the three elements calcium, carbon and oxygen in a sample of calcium carbonate is given as :

Calcium = 40.0%; Carbon = 12.0%; Oxygen = 48.0%

If the law of constant proportions is true, what weights of these elements will be present in 1.5 g of another sample of calcium carbonate?