a. An aqueous solution is made by dissolving 18.4 grams of iron(III) bromide in
ID: 954745 • Letter: A
Question
a. An aqueous solution is made by dissolving 18.4 grams of iron(III) bromide in 314 grams of water.
The molality of iron(III) bromide in the solution is ________m.
b.In the laboratory you are asked to make a 0.473 m chromium(II) acetate solution using 425 grams of water.
How many grams of chromium(II) acetate should you add?
_________ grams.
c. The boiling point of diethyl ether CH3CH2OCH2CH3 is 34.50°C at 1 atmosphere. A nonvolatile, nonelectrolyte that dissolves in diethyl ether is chlorophyll.
If 10.38 grams of chlorophyll, C55H72MgN4O5 (893.5 g/mol), are dissolved in 236.2 grams of diethyl ether.
The molality of the solution is ______ m.
The boiling point of the solution is______ °C.
d. The freezing point of benzene C6H6 is 5.50°C at 1 atmosphere. A nonvolatile, nonelectrolyte that dissolves in benzene is DDT .
If 14.38 grams of DDT, C14H9Cl5 (354.5 g/mol), are dissolved in 276.5 grams of benzene ...
The molality of the solution is _____ m.
The freezing point of the solution is _________°C.
Explanation / Answer
a. An aqueous solution is made by dissolving 18.4 grams of iron(III) bromide in 314 grams of water.
Number of moles of iron(III) bromide = 18.4 g/ 295.56 g/mol
= 0.062 mol iron(III) bromide
molality of iron(III) bromide = number of moles / solvent in Kg
= 0.062 mol iron(III) bromide /0.314 kg
=0.197 m
The molality of iron(III) bromide in the solution is 0.197 m .
b.In the laboratory you are asked to make a 0.473 m chromium(II) acetate solution using 425 grams of water.
Given that m = 0.473 m = number of moles / solvent in Kg
Number of moles = 0.473 moles / kg * 0.425 Kg
=0.20 mol
molar mass of chromium(II) acetate= 229.13 g/mol
Now calculate the amount of 0.20 mol of chromium(II) acetate :
229.13 g/mol*0.20 mol
= 46.1 g
How many grams of chromium(II) acetate should you add?
46.1 grams.
c. The boiling point of diethyl ether CH3CH2OCH2CH3 is 34.50°C at 1 atmosphere. A nonvolatile, nonelectrolyte that dissolves in diethyl ether is chlorophyll.
If 10.38 grams of chlorophyll, C55H72MgN4O5 (893.5 g/mol), are dissolved in 236.2 grams of diethyl ether.
Number of moles = 10.38 grams of chlorophyll/ 893.5 g/mol= 0.012 mol
Mass of solvent in kg= 0.2362 kg
Molality = 0.012 mol/ 0.2362 kg=0.051 m
The molality of the solution is _0.051 _____ m.
Given that
The boiling point of diethyl ether CH3CH2OCH2CH3 is 34.50°C
The value of Kb for diethyl ether is 1.824 °C kg/mol
Change in BP = Kb m where Kb is the boiling point elevation constant for diethyl ether
Change in BP = 1.824 °C kg/mol*0.051 mol/kg
Change in BP = 0.093 °C
Boiling point of solution = 34.50°C+ 0.093 °C=34.593 °C
The boiling point of the solution is34.593 °C
d. The freezing point of benzene C6H6 is 5.50°C at 1 atmosphere. A nonvolatile, nonelectrolyte that dissolves in benzene is DDT .
If 14.38 grams of DDT, C14H9Cl5 (354.5 g/mol), are dissolved in 276.5 grams of benzene ...
Number of moles = 14.38 grams of DDT / 354.5 g/mol= 0.041 mol
Mass of solvent in kg= 0.2765 kg
Molality = 0.041 mol/ 0.2765 kg=0.15 m
The molality of the solution is _0.15_____ m.
Given that
The freezing point of benzene C6H6 is 5.50°C
The value of Kf for benzene is 4.90 C/m
dT = kf x m = 4.90 C/m x 0.15 m = 0.735 C
The f.p. is 5.50 - 0.735 = 4.765 C
The freezing point of the solution is _4.765 _°C.
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