A solution of 3.00 g of which substance, dissolved in 100 g H2O, has the highest

Question

A solution of 3.00 g of which substance, dissolved in 100 g H2O, has the highest boiling point? (A) HOCH2CH(OH)CH2OH (M = 92.1) (B) RbF (M = 104.5) (C) AlCl3 (M = 133.3) (D) TlNO3 (M = 390.4)
The answer is C but why A solution of 3.00 g of which substance, dissolved in 100 g H2O, has the highest boiling point? (A) HOCH2CH(OH)CH2OH (M = 92.1) (B) RbF (M = 104.5) (C) AlCl3 (M = 133.3) (D) TlNO3 (M = 390.4)
The answer is C but why A solution of 3.00 g of which substance, dissolved in 100 g H2O, has the highest boiling point? (A) HOCH2CH(OH)CH2OH (M = 92.1) (B) RbF (M = 104.5) (C) AlCl3 (M = 133.3) (D) TlNO3 (M = 390.4)
The answer is C but why

Explanation / Answer

dela t=Kb x m x i

For AlCl3

i=4 because 1 Al and 3 Cl.

kb = ebullioscopic constant = 0.512 C / m

m=(3/133.5)/0.1=0.2247

delta t=4*0.512*0.2247=0.46

For HOCH2CH(OH)CH2OH (glycerol)

m=(3/92.1)/0.1=0.3257

i=1

Kb=0.51

delta t=1*0.51*0.3257=0.166

For RbF

m=(3/104.5)/0.1=0.287

i=2

So Kb will be very small so delta t=2*0.287*kb=0.574Kb will be less than that of AlCl3.

Highest delta t is of AlCl3

For TiNO3 molar mass is very high so molality will be very low so delta t will be very loss, so this cant be the choice

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