Question

The pH of rainwater, is approximately:
A. 6.5
B. 7.5
C. 5.6
D. 7.0

Answer 1

Hint: We have studied that in chemistry pH is a chemical property which defines the acidity and basicity of chemical compounds. pH can be measured by many instruments or using litmus paper as well.

Complete step by step answer:
Water from oceans, rivers, ponds and lakes evaporates and forms clouds. When temperature near the clouds drops, the vapour condenses and forms water droplets. These droplets fall down on the earth’s surface in the form of rains. Since, water from these reservoirs on land already has some ions dissolved in them, the pH of water drops as the water mixes.
Normal water has a pH value of $7$ i.e., it is considered as neutral. But the rain water mixes with many other gases and pollutants and hence its pH value is low. It ranges from $5$ to $6$ which is slightly acidic.
When gases like sulphur dioxide and mix with the rain water, the pH of water drops to $4$and water becomes very acidic. Hence, this type of rain is called acid rain. The corrosion (yellow appearance) of Taj Mahal’s limestone is the result of acid rain.

So, the correct answer is Option C.

Note: For our knowledge, pH is also defined as the power of hydrogen which is used to measure the quantity of ${H^ + }$ ions in the solution. In a solution, two components are present, solute and solvent. Solute is the part which gets dissolved in a solvent which is mostly liquid. On dissolution the amount of hydrogen and hydroxide ions changes due to which the acidity or the basicity of a solution is determined. When the amount of ${H^ + }$ ions in the solution increases in comparison to $O{H^ - }$ ions then the solution becomes acidic where the pH value is less than $7$. And when bases are dissolved in a solvent, the amount of $O{H^ - }$ ions increases in comparison to ${H^ + }$ ions and the solution becomes basic where the pH value is more than $7$.