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Determination of CuSO4 solution concentration using UV-Visible

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					Science & Engineering Lab 2 Experiment E

BKC 1721

Concentration Dependence of Absorbance Values using UV-Vis Spectrometer

Objectives

1. To determine absorbance of solutions at different concentration. 2. To determine the concentration of given sample.

Introduction

A UV-vis Spectrophotometer is a research instrument used to gather information about a chemical sample. It exposes a chemical solution to the ultraviolet and visible region of the electromagnetic spectrum. Depending on the type of chemical, a certain amount of the light gets absorbed by the chemical which causes electrons to be promoted from one energy level to another. The amount of light that reaches the detector is then recorded as a spectrum. A spectrum is a graphical representation of the amount of light absorbed or transmitted by matter as a function of the wavelength. A UV-visible spectrophotometer measures absorbance or transmittance from the UV range to which the human eye is not sensitive to the visible wavelength range to which the human eye is sensitive.

Reagents and Equipment

1. CuSO4 2. Distilled water 3. 1 500 volumetric flask 4. 4 100-ml volumetric flasks 5. Disposable glass pipettes (minimum 6) 6. 10-mm path length quartz cell

____________________________________________________________________ Faculty of Chemical & Natural Resources Engineering, KUKTEM

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Science & Engineering Lab 2

BKC 1721

Method

1. Prepare a CuSO4 stock solution of about 14 g in 500 ml distilled water. 2. Prepare four sample solutions in the 100-ml volumetric flasks by diluting the stock solution: sample concentrations: 14, 7, 3.5, 1.75 g/l. 3. Add a small amount of NaCl (< 0.1 mg) in a 100-ml volumetric flask and fill the flask with the stock solution. Label this sample as X. 4. Measure a reference on distilled water. 5. Measure the absorbance values at 800 nm of the stock solution and of each of the other solutions. 6. Repeat step 5 for sample A, B and C.

Evaluation

1. Enter the concentrations of the five solutions you prepared in the list below.

c1

=

g/l g/l g/l g/l g/l

c2 = c3 c4 c5 = = =

____________________________________________________________________ Faculty of Chemical & Natural Resources Engineering, KUKTEM

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Science & Engineering Lab 2 2. Enter your measured absorbance values in the tables 1.

BKC 1721

Table 1: Measured absorbance values at different concentrations

Sample solution c1 c2 c3 c4 c5 cX cA cB cC

Absorbance (AU)

Questions

1. Plot absorbance of c1, c2, c3, c4, and c5 as a function of concentration. 2. Determine the concentration of sample A, B and C. 3. Explain why the absorbance value for c1 and cX are different?

____________________________________________________________________ Faculty of Chemical & Natural Resources Engineering, KUKTEM

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