8.0575 x 10-2 kg of Glauber's salt are dissolved
in water to obtain 1 dm? of a solution of density
1077.2 kg m-3. Calculate the molarity, molality, and
mole fraction of Na2SO4 in the solution.
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Answer:
The formula for Glauber's salt is Na
2
SO
4
⋅10H
2
O.
Given mass =8.0575×10
−2
kg=80.575kg
Molecular weight =322gmol
−1
Molecular weight of Na
2
SO
4
=142gmol
−1
Mass of Na
2
SO
4
in 80.575 g sampe =
322
142
×80.575 =35.53g
Molarity (M) =
142
35.52
×1=0.2502M
Density=1077.2kgm
−3
=1077.2gL
−1
Density=
Volume
Mass
Mass of solution =density×volume =1077.2×1=1077.2g
Mass of water =1077.2−35.53=1041.67g
Molality(m)=
142
35.53
×
1041.67
1
×100=0.2402
Moles of Na
2
SO
4
=
142
35.53
=0.2502
Moles of H
2
O=
18
1041.67
=57.87
Moles fraction (Na
2
SO
4
)=
Total Moles
Moles ofNa
2
SO
4
=
0.2502+57.87
0.2502
=4.304×10
−3
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