Dr.S. H. Burungale

1. Analysis of Pollutants
By
Dr. S.H. Burungale
Department of Chemistry
Yashwantrao Chavan College of Science Karad

78. Analysis of Lead
Gravimetric Analysis

79. Gravimetric Determination of Lead Chromate
SOLUTIONS Concentrated NaOH
pH meter
0.1% Nitric Acid
(Conc. HNO3 = 76%, so about 1 mL conc./100 mL water)
0.10 M chromium nitrate, Cr(NO3 )3 09H2O (4 g/100 mL)
0.12 M potassium bromate, KBrO3 (2 g/100 mL)
Acetate buffer solution: 6 M in acetic acid, 0.6 M in sodium acetate.
GLASSWARE
2 erlenmeyer flasks
2 porous porcelain filter crucibles suction adapters

80. PROCEDURE 1. To eache flask add 4 mL of 1000 ppm Pb. Bring to 20 mL
vol.. To the fifth flask add 20 mL of one of your soil sample digests. To one of
the first four (lead standard) flasks add 4 mL of 1000 ppm Zn.
2. If necessary, neutralize 20mL solution with NaOH to pH 7 (use indicator
paper) in a 100 mL beaker. Solution will be slightly cloudy. What is the
chemistry that makes it cloudy?
3. Adjust volume of sample to about 20 mL.
4. Add 10 mL Cr(NO3 )3 09H2O solution and 10 mL of KBrO3 . Solution will
be clear blue.
5. Heat but do not boil for 30 minutes.
6. When solution is clear and yellow (= measure of extent of chromic
oxidation), add 10 mL of buffer and heat 5 more minutes. 7. Weigh your 6 filter
crucibles.
8. Cool the mixture and filter off the lead chromate on a sintered glass or porous
porcelain filter crucible.
9. Wash the precipitate with 2 or 3 small portions of 0.1% nitric acid.
10. Dry at 120C for 30 minutes.
11. Cool and weigh as PbCrO4 (Pb/PbCrO4 = 0.641108)

81. Direct Titration of Lead with ErioT and EDTA
Lead is held in solution by weakly chelating tartrate so that it may
react with Erio T to form a bluish violet color. The lead is titrated
with standard EDTA. The end point is observed by a loss of the
bluish violet color as the last of the lead-Erio-T complex is
consumed.

82. Reagents 0.01 M lead solution
0.01 M EDTA standard solution: Dilute from 0.100 M
EDTA 37.22 g of disodium EDTA in 1000 mL deionest
water. Or Dry the acid for two hours at 130-150C.
Cool. Weigh 29.210 g of acid EDTA, add to 600 mL
water, add pellet by pellet NaOH, until the EDTA
comes into solution. Dilute to 1L.
Erio T indicator powder: Grind 100 mg of indicator
with 10 g of NaCl to a very fine powder and store.
Tartaric acid pH 10 buffer : Dissolve 70 g of NH4Cl in
570 ml of ammonia ( s. G. 0.90) and dilute to distilled
water to 1 L.

83. Procedure 1. Place 10-30 ml (exactly measured) 0.01 M
lead soluiton in 250 ml flask
2. Add a spatula end of tartaric acid.
3. Add 5 ml of buffer pH 10 and dilute to about 50-100
ml. If a turbidity occurs (Pb(OH)2 ) add more tartaric
acid.
4. Add Erio T (too much will change the color intensity,
so start small).
5. Titrate until the colour changes from violet just to
clear blue.
6. Repeat twice to be able to report the rsd of the
method.
1 ml 0.01 M EDTA = 2.0719 mg Pb

84. Spectrophotometry
For the determination of small amounts of lead (0.005-0.25 mg)
advantage is taken of the fact that when a sulphide is added to a solution
containing lead ions a brown colour, due to the formation of colloidal
lead sulphide, is produced. However, for general use the dithizone
method
Reagents. Standard lead solution. Dissolve 0.160 g of analytical grade
lead nitrate in 1 L of distilled water; 10.0 mL of this solution, diluted to
250 mL gives a working solution containing 4 pg of lead mL-'.
Dithizone reagent. Dissolve 5 mg of the solid in 100 mL of chloroform
Ammonia-cyanide-sulphite solution. Prepare by diluting 35 mL of
concentrated ammonia solution and 3.0mL of 10 per cent potassium
cyanide solution to 100 mL and adding 0.15 g of sodium sulphite.

85. Procedure.
Place 10.0 mL lead solution in a 250 mL separatory
funnel, add 75 mL of the ammonia-cyanide-sulphite solution and
then by the cautious addition of dilute hydrochloric acid adjust the
pH of the solution to 9.5 (pH-meter).
Now add 7.5 mL of the dithizone reagent to the separatory funnel,
followed by a further 17.5 mL of chloroform. Shake for 1 minute,
allow the layers to separate, then remove the chloroform layer.
Measure the absorbance of this against a blank solution, using a 1
cm ce11 and a wavelength of 510 nm (green filter). Repeat the
procedure with 5.0mL, 7.5 mL and 15.0mL portions of the working
lead solution and then with 10mL of the test solution.

86. Determination of Lead by Amperometric
Titration

120. The chromium in the substance is converted into chromate or
dichromate by any of the usual methods. A platinum indicator
electrode and a saturated calomel electrode are used. Place a
known volume of the dichromate solution in the titration
beaker, add 10mL of 10 per cent sulphuric acid or
hydrochloric acid per 100 mL of the final volume of the
solution and also 2.5 mL of 10 per cent phosphorus(V) acid.
Insert the electrodes, stir, and after adding 1 mL of a
standard ammonium iron(I1) sulphate solution, the e.m.f. is
measured. Continue to add the iron solution, reading the e.m.f.
after each addition, then plot the titration curve and determine
the end point.
Determination of chromium

121. Thank You