Question 21

# The following data are obtained when dinitrogen and dioxygen react together to form different compounds:Mass of dinitrogen         Mass of dioxygen(i) 14 g                                  16 g(ii) 14 g                                 32 g(iii) 28 g                                 32 g(iv) 28 g                                 80 g(a) Which law of chemical combination is obeyed by the above experimental data?Give its statement.(b) Fill in the blanks in the following conversions:(i) 1 km = ...................... mm = ...................... pm(ii) 1 mg = ...................... kg = ...................... ng(iii) 1 mL = ...................... L = ...................... dm3

Let us fix 14 parts by weight of nitrogen as fixed weight.

Now let us calculate the weights of oxygen which combine with 14 parts by weight of nitrogen

 Sno No of parts by weight of nitrogen No of parts by weight of oxygen 14 parts of nitrogen as fixed weight No of parts by weight of oxygen which combine with 14 parts by weight of nitrogen 1 14g 16g 14g 16 2 14g 32g 14g 32 3 28g 32g 14g 32 4 28g 80g 14g 80

(a)  If we fix the mass of dinitrogen at 14 g, then the masses of dioxygen that will combine with the fixed mass of dinitrogen are 16 g, 32 g, 32 g, and 80 g.

The masses of dioxygen bear a whole number ratio of 1:2:2:5. Hence, the given experimental data obeys the law of multiple proportions.

This law was given by Dalton in 1804. The law states that if two elements combine to form 2 or more compound, then the weight of one element which            combines a  fixed weight  of other element in these compounds,bears a simple whole number ratio by weight.

(b) (i) We know 1km=1000m

Or 1m = 1000 mm

Therefore 1km = 1000x 1000mm= 106 mm

1 km = 1 km ×

1 km = 1015 pm

Hence, 1 km = 106 mm = 1015 pm

(ii)  We know 1kg = 1000mg

Or 1000mg= 1kg

Or 1mg= 1/1000* 1= 0.01 kg

1 mg = 1 mg ×

⇒ 1 mg = 106 ng

1 mg = 10–6 kg = 106 ng

(iii)  We know 1000 ml=l L

Or 1ml=1/1000*1= 0.01L

1 mL = 1 cm3 = 1 cm3

⇒ 1 mL = 10–3 dm3

1 mL = 10–3 L = 10–3 dm3