Title: Which Iron Compound is it?

Author: x

Group Number: 5

Date: May 28, 2014

I. Objective: To determine the amount of iron in the four unknown compounds tested.

II. Introduction: The objective of this lab is to determine the amount of iron in each of the unknown compounds tested, and this will be done using spectroscopy. Each sample is placed in a cuvette then using electromagnetic radiation, the sample will absorb some of the wavelengths, while others pass through the substance. The amount of light passed through the substance compared to the intensity of light that leaves the substance is compared in a ratio then converted to a percentage and that gives the transmittance, which then later is related to absorbance. The Beer’s law plot is derived from the Beer-Lambert law where: A=εbC. Epsilon is proportionality constant called the molar absorptivity, b is the thickness of the solution in the light path and usually remains constant for experiments, and C is the molarity of the absorbing species in the solution (Bauer 99). The Beer-Lambert law can be transformed into slope-intercept form and then used to make a graph, or plot of the data, called a Beer’s law plot. Using the dilution formula, the concentration can be calculated, and plotted against the absorbance value given from using the spectrophotometer. Plotting these against each other gives a line, with a slope that we can interchange the values from the unknowns to see how much light was absorbed for each sample.

III. Data and Results:

1. Reagents Used and Concentrations from bottles.

Reagents

Concentration

FeNH4(SO4)2∙12H2O 0.004985 M

HNO3

6 M

KSCN

0.004985 M

Unknown 1

Unknown 2

Unknown 3

Unknown 4

2. Known Solutions Trial Number:

1

2

3

4

5

6

Volume FeNH4(SO4)2∙12H2O

1.20mL

1.40mL

1.00mL

0.80mL

1.80mL

Volume HNO3

1.00mL

1.00mL

1.00mL

1.00mL

1.00mL

Volume KSCN

2.00mL

2.00mL

2.00mL

2.00mL

2.00mL

Volume water

15.8mL

15.6mL

16.0mL

16.2mL

15.2mL

Concentration Fe3+

2.98x10-4

3.47x10-4

2.98x10-4

1.98x10-4

4.46x10-4

Absorbance Value

0.90184

1.05900

0.77743

0.5454

1.33620

Wavelength of Amax

480 nm

M Absorbtivity Coefficient

3.194

Correlation coefficient

0.993

*Two of the seven trials we initially conducted were dropped because they were outliers from our other data, and doing so they wouldn’t skew our Beer’s law plot.

3. Attach or insert Beer’s law plot.

4. Unknown Solutions

Unknown Letter _A______________

Trial Number:

1

2

3

Volume Unknown 1

1.00mL

1.00mL

1.00mL

Volume HNO3

1.00mL

1.00mL

1.00mL

Volume KSCN

2.00mL

2.00mL

2.00mL

Volume water

16.00mL

16.00mL

16.00mL

Absorbance Value

0.88576

0.86520

0.9795

[Fe3+] in diluted

5.8x10-3

5.06x10-3

5.26x10-3

[Fe3+] in undiluted

2.59x10-4

2.53x10-4

2.63x10-4

Mass Fe (per Liter) in undiluted

0.2896

0.2824

0.2938

Percent Fe

24.8%

24.19%

25.17%

Average % Fe

24.72%

Standard Deviation

In average values

+ 0.2

Identity of unknown

FeCl3•6H2O

Percent Error

Unknown Letter _B_______________

Trial Number:

1

2

3

Volume Unknown 1

1.00mL

1.00mL

1.00mL

Volume HNO3

1.00mL

1.00mL

1.00mL

Volume KSCN

2.00mL

2.00mL

2.00mL

Volume water

16.0mL

16.00mL

16.00mL

Absorbance Value

0.88472

0.91170

0.89677

[Fe3+] in diluted

0.000258

0.000267

0.000262

[Fe3+] in undiluted

0.00517

0.00531

0.00525

Mass Fe (per Liter) in undiluted

0.28919g

0.2986g

0.2931g

Percent Fe

11.39%

11.77%

11.56%

Average % Fe

11.57

Standard Deviation

In average values

Identity of unknown

Fe(NH4)(SO4)2•12H2O

Percent Error

Unknown Letter _C_______________

Trial Number:

1

2

3

Volume Unknown 1

1.00mL

1.00mL

1.00mL

Volume HNO3

1.00mL

1.00mL

1.00mL

Volume KSCN

2.00mL

2.00mL

2.00mL

Volume water

16.00mL

16.00mL

16.00mL

Absorbance Value

0.74251

0.76317

0.76031

[Fe3+] in