The document describes procedures for determining the pH of water and soil samples using a pH meter. pH measures how acidic or basic a substance is on a scale of 0-14. The water sample tested was found to have a neutral pH of 7.3, while the soil sample had a slightly acidic pH of 6.5, which is optimal for plant growth as most nutrients are available within this range. Calibration of the pH meter and consideration of temperature effects are important for accurate pH measurement.

1. DETERMINATION OF pH FOR
WATER & SOIL
ARULARASI A.
2019223028
M. E. IWM
Water Quality Laboratory – IW 5302

2. Introduction
 pH is a measure of how acidic/basic water is.
 The range goes from 0 to 14, with 7 being neutral.
 pH of less than 7 indicate acidity, whereas a pH of greater than 7 indicates a base.
 pH is really a measure of the relative amount of free hydrogen and hydroxyl ions in the water.
 Water that has more free hydrogen ions is acidic, whereas water that has more free hydroxyl ions is
basic.
 pH is reported in "logarithmic units". pH = -log [H]
 Since pH can be affected by chemicals in the water, pH is an important indicator of water that is
changing chemically.
 Each number represents a 10-fold change in the acidity/basicness of the water.

3. Introduction
 Water with a pH of five is ten times more acidic than water having a pH of six.
 Not only does the pH of a stream affect organisms living in the water, a changing pH in a stream
can be an indicator of increasing pollution or some other environmental factor.
Source: https://www.jansanconsulting.com/uploads/5/5/5/8/55581447/ph-scale_orig.jpg

4. Why pH test?
 The pH of water determines the solubility (amount that can be dissolved in the
water) and biological availability (amount that can be utilized by aquatic life) of
chemical constituents such as nutrients (phosphorus, nitrogen, and carbon) and
heavy metals (lead, copper, cadmium, etc.).
 pH of soil is so important to plant growth because it determines the availability of
almost all essential plant nutrients. At a soil pH of 6.5, the highest number
of nutrients are available for plant use.

5. Aim:
To determine the pH of the water and the soil
Apparatus Required:
 pH meter with electrodes
 Distilled Water
 Standard Buffer solutions with
pH of 4, 7 and 10
 50 ml glass beaker
 Thermometer
 Glass stirring rod
 Weighing Machine
 Soil sample
 Water sample
 Watch glass
 No. 10 Sieve (2mm mesh)
 Tissue paper
 Spatula

6. Calibration
 For very precise measurement, the pH meter should be calibrated before each measurement.
The calibration should be performed with at least two buffer solutions with known pH.
 For general purposes, buffer solutions with pH 4 and pH 10 are used. For more precise
measurements, three buffer solution calibrations are preferred.
 After each single measurement, the bulb is rinsed with distilled water or deionised water to
remove any traces of solution being measured. Then the bulb is blotted with a blotting paper to
remove remaining water that could dilute the sample and alter the reading.
 Do not wipe the electrodes, as this may result in polarization of the electrode and consequent
slow response.
 Any cause of slow response due to the polarization can be solved by washing the electrodes
thoroughly.
 When not in use, the bulb must be kept wet at all times to avoid dehydration of the pH sensing
membrane.

7. Procedure for water
The water sample is properly mixed and stirred using a glass rod.
By using a watch glass, sample of water equal to 40 ml ± 5 ml is added to the beaker.
Let the sample stand for a minimum of one hour to allow the temperature to stabilize, stirring it occasionally while
waiting. Measure the temperature of the sample and adjust the temperature controller of the pH meter to that of the
sample temperature.
Standardize the pH meter by means of the standard solutions provided.
Immerse the electrodes of the pH meter into the water sample and turn the beaker slightly to obtain good contact
between the water and the electrodes.
The electrodes require immersion 30 seconds or longer in the sample before reading to allow the meter to stabilize.
Read and record the pH value to the nearest tenth of a whole number. Rinse the electrodes well with distilled water,
then dab lightly with tissues to remove any film formed on the electrodes.

8. Sample preparation for soil
 Air dry the soil sample.
 Sieve the soil sample through a No. 10 sieve (2 mm mesh) to remove the coarser soil fraction
 Weigh out approximately 10 g of the air-dried and sieved soil sample.
 Place the soil into a glass container and add approximately 10 ml of distilled or de-ionized
water.
 Stir to obtain a soil slurry and let stand for 1 hour stirring every 10 to 15 minutes. This is to
allow the pH of the soil slurry to stabilize.
 After one hour, measure the temperature of the suspended soil sample. Set the temperature dial
on the pH meter to match the measured temperature.

9. Procedure for soil sample
 Calibrate the electrodes with the standard buffer solution. It is a solution offering resistances.
 Before immersing the electrodes into the sample, stir the sample well with a glass rod.
 Place the electrodes into the soil slurry solution and gently turn beaker to make good contact
between the solution and the electrodes.
 Care should be taken that electrodes are not placed into the soil; only into the soil slurry
solution.
 Dip the electrode into the sample solution wait upto 1 min for steady reading in the pH meter
reading.
 Read and record the pH value to the nearest tenth of a whole number.

10. Observation
 The value displayed is read directly as pH. The
temperature of the samples and calibration buffers
should be identical to ensure accuracy.
 Record the sample temperature with the pH value
obtained.
Sample values:
Sample Name Temperature pH Value
Water 32.5 7.3
Soil sample 31 6.5

11. Inference
• The pH of the given water sample is 7.3, therefore it is
neutral with negligible alkaline contents in the given
water sample.
• The pH of the given soil sample is 6.5, therefore it is
concluded that the given sample of soil is slightly acidic
which is an essential parameter for the plant growth
where most of the nutrients are available in this range of
pH.

12. References
•TEST METHOD FOR THE DETERMINATION OF pH VALUE OF WATER OR SOIL
BY pH METER https://www.dot.ny.gov/divisions/engineering/technical-
services/technical-services-repository/GTM-24b.pdf.
•Working of ph probe
https://www.pharmaguideline.com/2015/08/principle-and-working-of-pH-
probes.html
•https://theconstructor.org/environmental-engg/ph-of-water/19855/
•https://www.coleparmer.com/tech-article/soil-samples-ph-testing
•https://clu-in.org/download/ert/1844-r00.pdf