Q1: 80 kg of Na₂SO₄ (molecular weight = 142) is present in 330 kg of an aqueous solution. The solution is cooled such that. 80 kg of Na₂SO₄ .10H₂O crystals separate out. The weight fraction of Na₂SO₄ in the remaining solution is

ANS:B - 0.18

To solve this problem, we need to determine the weight fraction of Na2SO4 in the remaining solution after 80 kg of Na2SO4·10H2O crystals separate out. Let's first find the initial weight fraction of Na2SO4 in the solution before any crystallization occurs:

1. Initial Weight of Na2SO4 in the Solution:
   • Initial weight of Na2SO4 in the solution = 80 kg
   • Total weight of the solution = 330 kg
   • Initial weight fraction of Na2SO4 = (Initial weight of Na2SO4) / (Total weight of the solution)
   • Initial weight fraction of Na2SO4 = 80 kg330 kg330kg80kg​
2. Weight of Na2SO4·10H2O Crystals:
   • 80 kg of Na2SO4·10H2O crystals separate out.
3. Final Weight of Na2SO4 in the Solution:
   • Final weight of Na2SO4 in the solution = Initial weight of Na2SO4 - Weight of Na2SO4·10H2O crystals
   • Final weight of Na2SO4 in the solution = 80 kg - 80 kg = 0 kg
4. Final Weight Fraction of Na2SO4 in the Solution:
   • Final weight fraction of Na2SO4 = (Final weight of Na2SO4) / (Total weight of the solution)

Now, let's calculate the final weight fraction of Na2SO4: Initial weight fraction of Na2SO4=80 kg330 kgInitial weight fraction of Na2​SO4​=330kg80kg​ Final weight fraction of Na2SO4=0 kg330 kgFinal weight fraction of Na2​SO4​=330kg0kg​ Final weight fraction of Na2SO4=0Final weight fraction of Na2​SO4​=0 Therefore, the weight fraction of Na2SO4 in the remaining solution after crystallization is 0.00.