This document describes a procedure to determine the concentration of sulfate ions (SO42-) in an unknown solution using nephelo-turbidity meter. Barium chloride is added to acidified samples containing varying concentrations of sulfate ions to form a barium sulfate suspension. The turbidity of each sample is then measured and a calibration curve is prepared by plotting turbidity readings against sulfate ion concentration. This curve is then used to determine the concentration of sulfate ions in an unknown sample based on its turbidity reading.

1. 1
INSTRUMENTALANALYSIS
LAB.
Mr Haydar A.M.S
BSc, MSc
Faculty of Science
Chemistry Department
Email: Haydar.kovly@gmail.com
University of Zakho Chemistry Department

2. 2
TURBIDIMETRIC DETERMINATION
OF SULPHATE ION (SO4
2- ) IN THE
UNKNOWN SOLUTION
Lab 8
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3. Aim of the experiment
3
To determine the concentration of SO4
2- in the unknown solution using
Nephelo-Turbidity meter.
University of Zakho Chemistry Department

4. 4
Introduction
When electromagnetic radiation (light) strikes a particle in solution, some of the light
will be
• absorbed by the particle,
• transmitted through the solution
• scattered or reflected.
The amount of light scattered is proportional to the concentration of insoluble
particle.
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5. Turbidimetry & Nephelometry
5
Introduction
 In turbidimetry, the intensity of light transmitted through the medium, the
unscattered light, is measured.
 Turbidimetric measurements are made at 180o from the
incident light beam.
University of Zakho Chemistry Department

6. Turbidimetry & Nephelometry
6
Introduction
In Nephelometry, the intensity of the scattered light is measured, usually, but not
necessarily, at right angles to the incident light beam.
Nephelometry
Turbidimetry
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7. Turbidimetry & Nephelometry
7
Introduction
 The intensity of scattered/transmitted light is normally measured by Nephelo-
turbidity meter.
 The turbidity standard unit is called
Nephelometric Turbidity Units (NTU).
University of Zakho Chemistry Department

8. Turbidimetry & Nephelometry
8
Introduction
cylindrical cells - flat faces to minimize reflections & multiple scatterings
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9. Required Apparatus
9
Introduction
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10. Applications of Turbidimetry or Nephelometry
• In the analysis of water, for the determination of turbidity, measure suspended solids
in waters and for the control of treatment processes.
• The concentration of a variety of ions can be determined using suitable precipitation
reagents to form suspensions.
• To find the end point of some titrations to form a suspension.
• To measure suspended particles in gases, like smog and fog.
10
Introduction
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11. 11
Introduction
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12. 12
Determination of sulphate ion
• In this experiment an unknown sample of sulfate ion is analysed with
turbidimetry. An excess of barium chloride is added to an acidified sample.
• The barium combines with sulphate in the sample to yield a barium
sulphate suspension
• In highly acidic solutions the only common ion which forms a precipitate
with sulphate is barium.
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13. 13
Determination of sulphate ion
Reagents & Chemicals
A. Standard sulfate solution: Weigh 0.18 g of potassium sulphate and dissolved in 1 L
distilled water. The stock solution which is prepared contains 100 mg/liter sulfate
ion.
B. Sodium chloride-hydrochloric acid reagent: Dissolve 12g of NaCl in 40 mL distilled
water, add 1mL of concentrated HCl then diluted to 50 mL.
C. Glycerol-Alcohol solution: prepare a mixture of 25 mL glycerol and 50 mL of
absolute ethanol.
D. Barium Chloride
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14. 14
Procedure
1. From sulphate ion stock solution prepare five working solution as shown in table
No. Conc. (ppm) V NaCl-HCl (mL) V Glycerol-alcohol (mL) V Volumetric Flask (mL)
Blank 0 2.5 5 25
1 10 2.5 5 25
2 15 2.5 5 25
3 20 2.5 5 25
4 25 2.5 5 25
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15. 15
Procedure
2. Add 0.2 g of BaCl2 to each flask stopper each flask and shake for 1 min, all the BaCl2
should dissolved.
3. Allow each flask to stand for 2-3 min and measure the turbidity.
4. Plot the reading against concentration of sulphate ion.
5. Determine the sulphate ion concentration of an unknown using the calibration
curve.
University of Zakho Chemistry Department