Delloyd's Lab-Tech Chemistry

LABGUIDE

Determination of Zinc by Atomic Absorption spectrometry

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Equipment: Atomic absorption Spectrophotometer

Sample: Three samples of known concentration given. (See Solutions Preparations below)

Apparatus:

10ml or 5ml burettes; grad pipettes 1ml, 2ml, 5ml; 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. 1000ppm 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 40ppm, 60ppm,and 80ppm, labeled A, B, and C, respectively.
4. 40ppm = 40mls of 1000ppm made up to 1 liter = A
    60ppm = 60mls of 1000ppm made up to 1 liter = B
    80ppm = 80mls of 1000ppm made up to 1 liter = C
5. 0.5% xylenol orange indicator (dissolve 0.5g in 100ml distilled water)
6. Hexamine. (provide solid)

Analytical notes:

1. Provide 100ppm Zn standard for AA measurements (Dilute 100ml of the 1000ppm to 1 liter solution, or 10ml 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. If there is no color change for blank, there is no zinc: Use blank value as zero.

Operation of Instrument:

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



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