University of Washington Chem 162 lab 4- All Answers are Correct (Graded A)

Name: Jordan Martel Quiz Section: CH Assigned
ID Number: 1666548 Lab Partner: Emerson Points

Chem 162 - Experiment #4
I. Fractional Crystallization of KNO3 with (NH4)2Fe(SO4)2·6H2O Impurity
II. The Solubility Curve of KNO3
Grading: 60 pts (10 pts notebook, 50 pts template) Note: 10
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DATA, CALCULATIONS, AND GRAPHS

Part I: Fractional Crystallization of KNO3 with (NH4)2Fe(SO4)2.6H2O Impurity
A. Starting Components (Fract. Crystallization #0) data entry 3

Step 3: Mixture before first crystallization 3

mass KNO3 4.470 g
mass (NH4)2Fe(SO4)2.6H2O 0.588 g
Total mass of the sample mixture 5.058 g
% Impurity (i.e., % Fe compound in the mixture)* 11.63 %
*(This is your % impurity for Fract. Crystallization # 0)

Fract. Crystallization #1
Step 7: mass of dry filter paper + watch glass 63.126 g

Step 10: mass of KNO3 crystals + filter paper + watch glass 66.717 g
mass of KNO3 crystallized 3.591 g
% KNO3 recovered (% of KNO3 in Step A.3.) 80.300 % 1

Step 11: mass of KNO3 crystals to be analyzed for purity in Part I.C 0.102 g



B. Fract. Crystallization # 2 (Re-crystallization)
Step 5: mass of dry filter paper + watch glass 63.128 g

Step 7: mass of KNO3 crystals + filter paper + watch glass 65.056 g
mass of KNO3 crystallized 1.928 g
% KNO3 recovered (% of KNO3 in Step A.3.) 43.100 % 1

Step 8: mass of KNO3 crystals to be analyzed for purity in Part I.C 0.405 g




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, C. Analysis to Determine % Impurity
First Crystallization
Step 3: Absorbance of the Fe(phen)32+ complex at 510 nm 1.79

Does the absorbance exceed the desired range (0 to 2.0 A)? _____no_______
If so, what dilution factor did you use in order to get the absorbance in the desired range? _____N/A________
2

What is your absorbance after dilution? (if applicable) N/A

Multiply your absorbance by the dilution factor (if applicable) N/A

Molar Absorptivity of ferroin, e
-1 -1
1.25E+04 M cm
Calculate the molarity of Fe2+ from the absorbance (pathlength = 1 cm) 0.000143 M
Type your calculation for molarity of Fe2+ (1 mol ferroin = 1 mol Fe 2+)
2
Molarity of Fe2+=(absorbance of Fe(phen)3 2+)/(molar absorbity of ferroin)*1cm
1.79/(1.25E+04 M^-1*cm^-1)*1cm)
=1.43E-04M

Volume of ferroin complex solution prepared in Steps C.1. and C.2. 0.0100 L
Calculate the moles of Fe2+ (moles of Fe2+= moles of (NH4)2Fe(SO4)2·6H2O) 1.43E-06 moles
Type your calculation for moles of Fe2+

moles Fe2+=(molarity of Fe2+)(volume of ferroin complex solution)
(1.43E-04M)(0.0100L) 2
=1.432E-06


Calculate the molar mass (NH4)2Fe(SO4)2·6H2O 392.15 g/mole
Calculate grams of (NH4)2Fe(SO4)2·6H2O in the crystals 0.0005616 g
Type your calculation for grams of (NH4)2Fe(SO4)2·6H2O

(NH4)2Fe(SO4)2*6H2O = (moles of Fe2+)(molar mass (NH4)2Fe(SO4)2*6H2O)
=(1.432E-06 moles)(392.15g/mole) 2
=5.616E-04

Mass KNO3 crystals analyzed for purity (from Step A.11.) (this cell will autofill from cell F41) 0.102 g
Calculate % mass of (NH4)2Fe(SO4)2·6H2O in the crystals 0.55 %
(This is your % impurity for Fract. Crystallization # 1)
Type your calculation for % mass of (NH4)2Fe(SO4)2·6H2O in the crystals.

(5.616E-04g/0.102g)*100 2
=0.55%




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