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Paper Topic:

Lab 7

Determining the Concentration of a Solution - Application of Beer 's Law

Candice Joseph

April 10 , 2007

1 . Purpose

The purpose of this experiment was to produce a calibration curve of absorbance vs . concentration for NiSO4 and then to use this standard curve for determining concentration of an unknown solution of NiSO4

2 . Introduction

Many transition compounds exhibit colors due to d-d transition . The electrons from the partially filled d-subshells absorb a particular wavelength from the white light (which is a mixture of the seven colors in rainbow ) and consequently

appear as the complementary color of the wavelength absorbed . If a material absorbs of the wavelength it appears colorless and in case it absorbs all it appears black . The list of complementary colors is typed below

Complementary colors

Red - Green , Blue - Orange , Violet - Yellow

Absorbance is a measure of the amount of light absorbed . This is determined by using Colorimeter , a type of spectrometer , which measures the quantity of light (in visible spectrum ) that passes through a sample . The absorbance increases with increasing concentration of the solution , since more the number of transition metal ions , more light is absorbed . There exists a linear relationship between absorbance and concentration of the solution

In this experiment we have used five standard NiSO4 solution i .e solutions with known concentration , to make a calibration curve between absorbance and concentration of NiSO4 solution

3 . Materials

IBM compatible computer , Serial box interface , Logger pro , Vernier Colorimeter , Cuvette , five large test tube (20x150 mm , Chemwipes , glass stirring rod , 30 mL of 0 .40 M NiSO4 , two 10 mL pipettes , pipet bulb distilled water , test tube rack , two 100 mL beakers , 5 mL of unknown NiSO4 solution

4 . Procedure

1 . Lab coat , gloves and safety glasses were used as safety measure during the experiment as the experiment involved handling of hazards chemicals

2 . Approximately 30 mL of 0 .40M NiSO4 stock solution was added to a 100 mL beaker . Another 30 mL of distilled water was added to another 100 mL beaker

3 . Five clean and dry large test tubes were marked numbers 1 - 5 . 2 , 4 6 , 8 and 10 mL of 0 .4 M NiSO4 stock solution was pipetted into test tubes numbered 1 to 5 , respectively . Also with another pipette 8 , 6 , 4 2 and 0 mL of distilled water was pipetted into the test tubes marked 1 to 5 , respectively . Thus NiSO4 standard solution measuring 10 mL with concentrations 0 .08M , 0 .16M , 0 .24M , 0 .32M and 0 .40M was obtained in test tubes numbered 1 , 2 , 3 , 4 and 5 respectively

4 . Computer was prepared for acquiring the data during the experiment The vertical axis had absorbance scaled from 0 to 0 .6 and the horizontal axis had concentration scaled from 0 to 0 .5M

Calibration of the Colorimeter

5 . The outside of the cuvette was cleaned and dried using a chemwipe and the cuvette was filled 3 /4th with distilled water in a manner to avoid bubbles in the solution...

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