EXPERIMENT 2: WATER ANALYSIS

COLOUR MEASUREMENT ON SUSPENDED SOLID DETERMINATION

1. Objective

This experiment described the method used to measure the presence of

suspended solids in water can impair the color measurement.

2. Introduction

A Lovibond comparator is used to place the color disc. It has two

compartments to hold a sample and distilled water. The samples were places into

nessleriser tubes. It is a comparison method without making standard solutions. One

of drawbacks of this method is it’s subjectively.

In Spectrophotometer method, an optimum wavelength was chosen. This

optimum wavelength ranges between 455 to 465 nm. A series of standard solutions

was made and read at a specified wavelength. The respond were then plotted against

platinum cobalt solution to produce a calibration graph. The respond from a sample is

then determined based on that calibration curve. Most modern equipment

incorporated the calibration graph into their equipment. It just needed to calibrate the

zero value with distilled water.

3. Theory

Color is a very subjective measurement of a water sample. One’s blue color

could be a green color to another eye. But in order to be a mentioned standard in

drinking water, it has to be measurable or quantify. The earliest method of quantifying

color is studied by Hazen. He made a series of standard color solution using a

platinum cobalt and gold. The color yield by 1 mg/l of platinum cobalt solution is

known as 1 color unit or Hazen unit. The presence of suspended solids can impair our

color measurement. The color of water given by unfiltered sample is known as

apparent color, while the color given by a filtered sample is referred as true color.

Indirectly it is the dissolved color of the sample.

The earliest approach by Hazen was by comparing the sample with a series of

standard solution. The one that matches the closest to the sample will be the color of

that sample. It is tedious and wasteful. Based on the same concept, a color disc is used

instead.

4. Apparatus

The lists of apparatus are:

Nessleriser tubes

Color discs

Sample vials

Spectrophotometer

Volumetric flasks, pipettes

5. Procedures

A few water samples are given to be analyzed. If the sample out of the color

range, then choose a higher color disc or dilute the sample accordingly. Compare the

reading obtained from comparator method with spectrophotometer method.

a) Firstly, sample is poured into nessleriser tube to the mark and the tube is

covered with the lid. Any built up of air bubble in the tube is avoided. The side

of the tube is dried with tissue paper.

b) Then, the tube is placed in the comparator and the color disc is rotated till the

color almost matches the sample. The reading is recorded.

c) After that, an aliquot of sample is transferred into a sample vial.

d) Next, a spectrophotometer is switched on and color measurement is chosen.

The instructed steps are followed.

e) Then, the distilled water is placed in and the reading set to zero, once it is

ready, the sample cell is placed in and read.

f) The reading is recorded.

6. Data recordings

Sample Lovibond reading Spectrophotometer reading

A 2.5 0.315

B 2.5 0.325

7. Discussion

From the data has been recorded, the Lovibond reading and

Spectrophotometer reading for sample A were recorded as 2.5 and 0.315 respectively.

Well, for sample B the Lovibond reading and Spectrophotometer reading were 2.5

and 0.325. Obviously, there is a discrepancies result in sample A compare to sample

B. There are few factors interfere with the readings, the sample vial and turbidity of

the sample. Even with a true solution, the sample vial will affect the reading due to its

materials.

Besides, as discussed before, color was very subjective measurement of water

sample. The result could be different to another eye by using a Lovibond comparator.

Even though recently with the advancement in optical technology, a better technology

is recommended, spectrophotometer. But some minor problems still cannot be

avoided. Especially when using spectrophotometer, when the optimum wavelength is

applied, the bult of spectrophotometer will affect the color of test sample. That is why

a huge discrepancy between both method. In order to reduce it, the best solution is

tried to apply a layer of coat on container.

8. Conclusion

Comparison between sample A and sample B, obviously sample B presence

more suspended solids compare to sample A. But, both results are less sensible due to

data obtained. The ideal material for color measurement is quartzite. When the color

is over range, a dilution is required.

9. Reference

Dr. Chua Kok Hua, 2007. “Water and Wastewater Laboratory Practices”.

College pf Engineering, University Tenaga National.

P. Aarne Vesilind, Susan M.Morgan, 2004. “Introduction to Environmental

Engineering”. Second Edition, Thompson Brooks/Cole.

10. Appendix

Figure 1: Sample A and sample B is prepared to be test.

Figure 2: Pour the sample into tube and close with the lid to avoid air bubble

Figure 3: Insert color disc to comparator and rotate it till match the color sample.

Figure 4: Lovibond Comparator and color disc

Figure 5: Spectrophotometer comparator Figure 6: A sample cell in tube is ready to put in spectrophotometer.