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Larutan a dibuat dengan mencampurkan 0,1 mol kbr dan 0,05 mol MgBr2 dalam 500 g air. Kedua garam ini terdisosiasi dengan derajat ionisasi 80% dan 70% dalam air. Larutan b dibuat dengan melarutkan 84 g urea (mr = 60) dalam 1 kg air. Perbandingan penurunan titik beku larutan a terhadap penurunan titik beku larutan b adalah ....
Accepted Answer
The ratio of freezing point depression of solution A to solution B is approximately 2.5:1. Here's how we can arrive at this answer:
Solution A
Calculate the molality of each salt:
Molality of KBr = (0.1 mol / 0.5 kg) = 0.2 mol/kg
Molality of MgBr2 = (0.05 mol / 0.5 kg) = 0.1 mol/kg
Calculate the effective molality considering the degree of ionization:
Effective molality of KBr = 0.2 mol/kg
0.8 = 0.16 mol/kg
Effective molality of MgBr2 = 0.1 mol/kg
0.7 = 0.07 mol/kg
Total effective molality of solution A = 0.16 mol/kg + (0.07 mol/kg
3) = 0.37 mol/kg (considering MgBr2 dissociates into 3 ions)
Solution B
Calculate the molality of urea:
Molality of urea = (84 g / 60 g/mol) / 1 kg = 1.4 mol/kg
Freezing Point Depression
ΔTf = Kf
m (where ΔTf is the freezing point depression, Kf is the cryoscopic constant of water, and m is the molality)
Since Kf is the same for both solutions, the ratio of freezing point depression is directly proportional to the ratio of molalities:
Ratio of ΔTf (A) : ΔTf (B) = 0.37 mol/kg : 1.4 mol/kg ≈ 2.5 : 1
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