Question

1g of a metal, having no variable valency, produces 1.67g of its oxide when heated in air. Its carbonate contains 28.57% of the metal. How much oxide will be obtained by heating 1g of the carbonate?
A. 0.4771
B. 0.54
C. 0.64
D. 0.5321

Answer 1

Hint: Valency it is the combining capacity of an atom. Certain elements have more than one valency such elements exhibit variable valency. It happens due to a pair of electrons remaining paired and not taking part in bonding (also called inert pair effect). The term oxidation state is referred to as valency.

Complete step by step answer:
From Avogadro’s law it is known that equal volumes of all gases contain equal numbers of molecules under similar conditions. Now since one mole of molecules of all gases contain the same number (6.022$ \times {10^{23}}$ ) of molecules, therefore they occupy the same volume under similar pressure and temperature. The mass of one mole of atoms is exactly equal to the atomic mass in grams of that element.
From the law of chemical equivalence it is known that the chemical substances react in the ratio of their equivalent masses. Now we are given that carbonate of the metal contains 28.57% of the metal. Now we know that ratios of the substance are equal to its grams then we can conclude that 100 grams of metal carbonate contains 2.57 gram metal then
100gm of metal carbonate will contain =28.57g of metal
So 1gm of carbonate will have = $\dfrac{{28.57}}{{100}} = 0.286$g of metal
Now according to the question,
1gm of metal produces =1.67gm of metal oxide
0.286 g of metal produces=$\dfrac{{1.67}}{1} \times 0.286 = 0.477g$
Hence the metal oxide produced by 0.286 g of metal is 0.477g.

Hence the correct option is option A.

Note:
Carbonate is an odourless gas. The question revolves around the mole concept. Carefully calculate the compounds. No variable valency means that the metal has a fixed oxidation state therefore valency factor does not affect the solution of the question.