Soil pH Measurement

Experiment 3: Soil pH measurement Introduction Aims The aims of the experiment were to determine the pH of a variety of soils which included sedentary, 3:2, sand, organic matter with the means of a pH meter at various soil water ratios and with or without calcium chloride. Method and Materials Samples of sedentary soil, 3:2 soil, sand, organic matter and compost, 100ml vials(x12), bottle of distilled water, analytical balance, pH meter, 2 buffer solution of known pH, 0.25M calcium chloride solution. Results Table 1- Average pH measurement for the given soil/water ratio in both without 0.01M calcium chloride and with 0.01M calcium chloride for different soil types. Note: The groups having the best data mentioned by the lecturer were chosen. Discussion When comparing the average pH measurement for all of the given soil/water ratios for both with and without the addition of 0.01M calcium chloride among the different types of soils, table 1 shows that sand has the highest pH, which is then followed by organic matter, compost, next being 3:2 soil and finally sedentary soil having the lowest pH of them all. The pH of soil pH is affected by both acid and base-forming ions. The acid forming cations are positively charged ions they commonly include hydrogen ions, aluminium ions ,and iron(II and III ions). Base forming cations commonly comprise of calcium ions, magnesium ions, sodium ions and potassium ions. It is also known that the CEC is positively correlated with soil pH. As the dilution of the soil solution increases, the pH is also seen to increase. The effect of adding water and occasional mixing during the 30 minute period is to allow the soil and the water to approach equilibrium conditions. Water will begin to progressively leach off the exchangeable basic ions present in the soil such as Ca2+, Mg2+, K+, and Na+. As a result hydrogen ions that will be now higher in concentration will compete and exchange with the basic ions for the