- State the uses of sulfuric acid in the manufacture of detergents and fertilisers; and as a battery acid.
- Describe the importance of controlling the pH in soils and how excess acidity can be treated using calcium hydroxide.
Acids and bases have use in more places than just the scientific laboratory. They come into play in our everyday life, from the digestion of food we eat to the products we use. Without acids and bases and their associated pH scale, many of the products that we depend on today will not have much of a use.
The pH of soil directly affects the life and growth of plants because it affects the availability of plant nutrients in the soil or fertiliser for plant use. Most plant nutrients are the most available at a slightly acidic pH, between 6.0 to 6.5. Any deviation of the soil pH away from this range will limit the growth of and in the long run result in the death of the plant.
Plants are heavily dependent on bacteria in the soil to break down and release nitrogen, from the organic matter or fertilizers found in the soil. This is as a nitrogen is a vital component of chlorophyll found on leaves and amino acids, which are the basic building block of proteins. These soil bacteria operates the best in the pH range of 5.5 to 7.0.
In addition, when soil acidity (or alkalinity) changes, the solubility of a number of metal ions essential or toxic for plant growth also change. For instance, aluminium can be dissolved at pH levels lower than 5.0, and when present in the ionic form, prevents cellular division and growth.
Furthermore, plant nutrients leach from the soil much faster at pH values below 5.5. This is especially prominent for large ions. Large ions do not stick tightly to soil particles and at low pH they are displaced by H+ and enter the soil solution. As the soil solution is drained off from the plant, the large ionic nutrient is lost with the soil solution.
Calcium hydroxide, also known as lime is often used to deal with the low pH and the resulting toxic effects of low pH of the soil. Calcium hydroxide reacts and neutralises the excess hydrogen ions to increase the pH of the soil.
However, if too much lime is added, the soil will become too alkaline and other gardening products such as sulphur is required to resolve the problem. Sulphur is converted to sulphuric acid by soil bacteria, leading to the neutralisation of the alkalinity in the soil.
With the increase in number of people in the global population, there is a higher demand for food. Threats in agricultural production such as pests, loss of soil fertility with each harvest and the lack of nutrients may result in low percentage of plants to harvest. Hence, fertilizers are often used to increase the nutrients available and to support the repeated growth of plants in a single plot of land.
Majority of the sulfuric acid produced by the chemical industry, is used to make phosphorus acid. In general, sulfuric acid is added to fluorapatite, which is also known as phosphorus rock or 3Ca3(PO4)2.CaF2 to give phosphoric acid and calcium sulfate (gypsum) along with some other insoluble impurities.
The phosphoric acid collected and reacted with other chemicals to produce salts of phosphoric acid. These salts are added into fertilizers, which are used as a supplement of phosphorus in phosphorous low or deficient soil. Phosphorus deficiency can be easily identified by the presence of the abnormally small plants, which are producing little or no flowers and have weak root systems or a bright green or purplish cast.
Production of Ammonium phosphate
Production of Superphosphate
Production of Sodium hydrogen phosphate (with concentrated NaOH)
In addition to fertilizers, sulfuric acid is also used in the production of batteries, detergents, papers and treatment of industrial waste water.