Question

Sebanyak 8 gram zat suatu non elektrolit yang rumus empirisnya CH2O dilarutkan dalam 250 gram air membeku pada suhu -0,331C jika Kf air=1,86 maka rumus molekul zat tersebut adalah

Answer 1

Massa terlarut = 8gr
massa pelarut = 250gr
kf air = 1,86
Tf larutan = -0,331
delta Tf = 0-(-0,331)
= 0,331
delta tf = kf x molalitas
0,331 = 1,86 x molalitas
molalitas = 0,331/1,86
molx1000/massa pel(gr) = 0,331/1,86
8/mr x1000/250 = 0,331/1,86
32/mr = 0,331/1,86
32 x 1,86 = 0,331 mr
59,52 = 0,331 mr
mr = 59,52/0,331
= 179,8
= 180

mr = 180
mr = x × (Ar C+ 2×Ar H + Ar O)
180 = x × (12+2+16)
180 = x × (30)
180/30 = x
6 = x

rumus molekul zat = x × (CH2O)
= 6 × (CH2O)
= C6H12O6