Question

Which aqeous solution will have the higher boiling point temperature?

a.) .100m NiBr2 (aq)

b.) .150m NH4NO3 (aq)

c.) .150Na2SO4 (aq)

d.) .100m MgSO4 (aq)

e.) .250m CH3OH (aq)

Answer 1

ΔTb = i*Kb*m

ΔTb is the elevation in boiling point

ΔTb will be maximum when i*m is maximum

Boiling temperature is maximum when ΔTb will be maximum

i is the number of ions that a compound can break into

a)

NiBr2

i = 3

NiBr2 breaks into 1 Ni2+ ion and 2 Br- ions

so,

i*m = 3*0.100 = 0.300

b)

NH4NO3

i=2 (1 NH4+ and 1 NO3-)

so,

i*m = 2*0.150 = 0.300

c)

Na2SO4

i=3 (2 Na+ and 1 SO42-)

so,

i*m = 3*0.150 = 0.450

d)

MgSO4

i=2 (1 Mg2+ and 1 SO42-)

so,

i*m = 2*0.100 = 0.200

e)

NH4NO3

i=1 (CH3OH doesn’t dissociate)

so,

i*m = 1*0.250 = 0.200

i*m is maximum for Na2SO4

So, maximum increase in boiling point will be for Na2SO4

So, maximum boiling temperature will be for Na2SO4

Answer: Na2SO4