Water can be obtained from various sources. Are all these samples of water chemically identical?
Yes, all purified samples of water obtained from various sources are chemically identical.
According to the Law of Constant Proportions, elements in a compound combine in a fixed ratio by mass, meaning they have definite proportions irrespective of their source.
When water collected from different sources like rivers, borewells, or oceans is purified and analysed, it always contains hydrogen and oxygen in a fixed mass ratio of 1:8. If 9 g of purified water from any source is decomposed, it will always yield exactly 1 g of hydrogen and 8 g of oxygen. Therefore, the chemical composition of water remains constant.
Explanation
The textbook context explains the Law of Constant Proportions, which states that elements in a compound have definite proportions by mass irrespective of its source. Using water as an example, it states that purified water from any source (rivers, borewells, oceans) always contains hydrogen and oxygen in a 1:8 mass ratio, proving they are chemically identical.