Answer:
(B) 42.1%
Explanation:
The formula for the calculation of moles is shown below:
![moles = \frac{Mass\ taken}{Molar\ mass}](https://tex.z-dn.net/?f=moles%20%3D%20%5Cfrac%7BMass%5C%20taken%7D%7BMolar%5C%20mass%7D)
Given: For ![Na_2S](https://tex.z-dn.net/?f=Na_2S)
Given mass = 15.5 g
Molar mass of
= 78.0452 g/mol
<u>Moles of
= 15.5 g / 78.0452 g/mol = 0.1986 moles</u>
Given: For ![CuSO_4](https://tex.z-dn.net/?f=CuSO_4)
Given mass = 12.1 g
Molar mass of
= 159.609 g/mol
<u>Moles of
= 12.1 g / 159.609 g/mol = 0.0758 moles</u>
According to the given reaction:
![Na_2S+CuSO_4\rightarrow Na_2SO_4+CuS](https://tex.z-dn.net/?f=Na_2S%2BCuSO_4%5Crightarrow%20Na_2SO_4%2BCuS)
1 mole of
react with 1 mole of ![CuSO_4](https://tex.z-dn.net/?f=CuSO_4)
0.1986 mole of
react with 0.1986 mole of ![CuSO_4](https://tex.z-dn.net/?f=CuSO_4)
Available moles of
= 0.0758 moles
Limiting reagent is the one which is present in small amount. Thus,
is limiting reagent. (0.0758 < 0.1986)
The formation of the product is governed by the limiting reagent. So,
1 mole of
gives 1 mole of ![CuS](https://tex.z-dn.net/?f=CuS)
0.0758 mole of
gives 0.0758 mole of ![CuS](https://tex.z-dn.net/?f=CuS)
Molar mass of
= 95.611 g/mol
Mass of
= Moles × Molar mass = 0.0758 × 95.611 g = 7.2473 g
Theoretical yield = 7.2473 g
Given experimental yield = 3.05 g
% yield = (Experimental yield / Theoretical yield) × 100 = (3.05/7.2473) × 100 = 42.1 %
<u>Option B is correct.</u>