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Experiments Overview

Complexation and atomic absorption
Determination of Zn by EDTA and atomic absorption

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Equipment:
Atomic absorption Spectrophotometer

Sample: Three samples of known concentration given.

Apparatus:

5 ml or 10 ml burettes, 50 ml burette, volumetric flasks 100ml, burette clamps and stands, pH 4 test paper, indicator bottles.

Chemicals:

EDTA (ethylene diamine tetra acetic acid) , or (ethylenedinitro) tetra acetic acid).
(HO2CCH2)2NCH2CH2N(CH2CO2H)2, FW = 292.24,
Zn metal,
Conc. HCl
Xylenol orange (indicator), Dye content = 90%
Hexamine (solid) - Hexamethylenetetramine FW = 140.19

Solutions preparation:

1. 0.1M EDTA standard soln. Dry salt in oven at 80°C, weigh out 37.225g and make up to 1 liter with distilled water.
2. 1000 ppm Zn standard. Dissolve 1g pure Zn metal in 30ml of 5M hydrochloric acid, and make up to 1 liter with distilled water.
3. Provide three Zn solutions of 40 ppm, 60 ppm,and 80 ppm, labeled A, B, and C, respectively.
4. 40 ppm = 40mls of 1000 ppm made up to 1 liter = A
60ppm = 60mls of 1000 ppm made up to 1 liter = B
80ppm = 80mls of 1000 ppm made up to 1 liter = C
5. 0.5% xylenol orange indicator (dissolve 0.5g in 100 ml distilled water)
6. Hexamine (hexamethylenetetramine), (provide solid)

Analytical notes:

1. Provide 100 ppm Zn standard for AA measurements (Dilute 100ml of the 1000 ppm to 1 liter solution, or 10 ml to 100 ml vol.)

2. Range for AA is 0.1ppm to 2.0ppm stds. (0.1, 0.5, 1.0, 1.5, and 2.0ppm)

3. The dilution factor for EDTA is 1 in 20 (0.005M)

4. The Zn solns. provided must be acidic. To ensure this, add 10mls conc. HCl to the preparation of each solution. (pH < 1)

5. No color change for blank means there is no Zn present. Use zero as value for blank.

Operation of Instrument:

Follow Users Guide. Obtain help and advice from Demonstrator or Technician




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