Question

The volume of $C{O}_2$ obtained at STP by the complete decomposition of 9.85 g $N{a}_{2}C{O}_3$ is:
(A) 2.25 litre
(B) zero
(C) 0.85 litre
(D) 0.56 litre

Answer 1

Hint: The sodium carbonate will produce from the decomposition of sodium bicarbonate. The chemical formula of sodium carbonate is $N{a}_{2}C{O}_3$ and is named as washing soda. When this sodium carbonate is heated it undergoes a thermal decomposition reaction.

Complete answer:
To calculate the number of moles of sodium carbonate,
$$numberofmolesofN{a}_2\text{C}{\text{O}}_3\text{=}{\displaystyle \frac{givenmassofN{a}_2\text{C}{\text{O}}_3}{\text{molar }massofN{a}_2\text{C}{\text{O}}_3}}$$
Given the mass of sodium carbonate = 9.58g
Molar mass of sodium carbonate ($N{a}_{2}C{O}_3=2XNa+1XC+3XO=2X23+1X12+3X16$ ) =106 g/mol
Substitute these values in the above equation of the number of moles of sodium carbonate,
$$numberofmolesofN{a}_2\text{C}{\text{O}}_3\text{=}{\displaystyle \frac{givenmassofN{a}_2\text{C}{\text{O}}_3}{\text{molar }massofN{a}_2\text{C}{\text{O}}_3}}\text{ =}{\displaystyle \frac{9.58g}{106g/mole}}=0.093mol$$
The thermal decomposition of sodium carbonate will take place above ${500}^{o}C$ . the reaction of decomposition is:
     $$N{a}_{2}C{O}_3(s)\to N{a}_{2}O(s)+C{O}_2(g)$$
(The name of the first reaction product is sodium oxide which is a solid and used in glassmaking and the name of the second product is carbon dioxide which is a gas)
By Stoichiometric of the above reaction:
1 mole of sodium carbonate produces 1 mole of carbon dioxide.
So, 0.093 moles of sodium carbonate will produce = 0.093 moles of carbon dioxide
At STP:
1 mole of a gas occupies 22.4 L of volume.
So, 0.093 moles of carbon dioxide will occupy = 0.093X22.4=2.08 L of carbon dioxide.
But, sodium carbonate is soda ash and it does not decompose at STP conditions. Hence carbon dioxide does not involve.

So, the correct answer is Zero liters. Option B

Note:
STP means Standard Temperature and Pressure, which denotes the same temperature of $0^{o}C$ (273.15K), but a slightly high pressure of 1 atm (101.325kPa). These values approximate the freezing temperature of the water and atmospheric pressure at sea level. One mole of any of a combination of gases occupies 22.4 L of volume at STP.