Determine the molality and mole fraction of a solution of 560 g of acetone,
CH3COCH, in 620 g of water.
Answers
Answer:
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Explanation:
Explanation:
You can calculate a solution's molality by keeping track of how many moles of solute you get in one kilogram of solvent.
This means that in order to calculate molality, you essentially need to know
how many moles of solute you have present
the mass of solvent expressed in kilograms
Now, you can determine how many moles of acetone,
(
CH
3
)
2
CO
, you get in that
560-g
sample by using the compound's molar mass.
In this case, acetone has a molar mass of
58.08 g mol
−
1
, which tells you that one mole of acetone has a mass of
58.08 g
.
This means that your sample contains
560
g
⋅
1 mole acetone
58.08
g
=
9.642 moles acetone
Now, your goal when finding molality is to find the number of moles of solute per kilogram of solvent. Convert the mass of water, which is your solvent, from grams to kilograms by using the conversion factor
∣
∣
∣
∣
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
a
a
1 kg
=
10
3
g
a
a
∣
∣
−−−−−−−−−−−−−−−
You will get
620
g
⋅
1 kg
10
3
g
=
0.620 kg
So, if
0.620 kg
of solvent hold a total of
9.642
moles of acetone, it follows that
1.0 kg
of solvent will hold
1
kg solvent
⋅
9.642 moles
0.620
kg solvent
=
15.55 moles
This means that your solution will have a molality of
16 molal
molality
=
b
=
∣
∣
∣
∣
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
a
a
16 mol kg
−
1
a
a
∣
∣
−−−−−−−−−−−−−−−