Question

Carbon dioxide can be obtained in a number of ways. For example,
a. By burning of coke in air.
b. By the thermal decomposition of lime stone.
c. By the action of dilute hydrochloric acid on washing soda.
Based on the information, answer the following questions:
i. Is the composition of the constituent elements is different in compounds obtained
from different sources?
ii. In what ratio are the two elements combined?
iii. In what ratio by mass are the two elements combined?
iv. Is the ratio a simple whole number?
v. Which law of chemical combination is supported?

Answer 1

Dear Student

From the informations given in the question,
a. C + O₂ $\stackrel{∆}{\to }$ CO₂
b. CaCO₃ $\stackrel{∆}{\to }$ CaO + CO₂
c. Na₂CO₃ + 2HCl $\underset{}{\to }$ 2NaCl + CO₂ + H₂O

(i) Composition of the constituent elements is same in all the cases i.e CO₂
(ii) C and O combine in the ratio of 1:2 since there is 1 C-atom and 2 O-atom in a molecule of CO₂
(iii) Since atomic masses of C and O are 12 u and 16 u respectively
Hence the ratio by mass in which the two elements are combined is 12:(16 x2) = 12:32 = 3:8
(iv) Yes the ratio a simple whole number (3:8)
(v) It obeys Law of definite proportion or Law of Constant Composition which states that a given chemical compound always contains its constituent elements in fixed ratio by mass irrespective of its source or method of preparation.

Regards