Question

When rain is accompanied by a thunderstorm, the collected rain water will have a \(\mathrm{pH}\) value: (a) Slightly lower than that of rain water without thunderstorm (b) Slightly higher than that when the thunderstorm in not there (c) Uninfluenced by occurrence of thunderstorm (d) Which depends on the amount of dust in air

Short answer

(a) Slightly lower than that of rain water without thunderstorm.

Step-by-step solution

Understanding Rain and Thunderstorms

When rain occurs alongside a thunderstorm, the electrical activity (lightning) can cause nitrogen and oxygen in the air to react, forming nitrogen oxides. These oxides then dissolve in rainwater, forming acids like nitric acid, which can lower the pH of the rainwater.

Assessing pH Influence

Under a thunderstorm, the additional acidic components from nitric acid will make the rainwater more acidic than it would be without a thunderstorm.

Evaluating Options

- (a) Slightly lower than that of rain water without thunderstorm: This matches our understanding that the pH is lowered due to acids. - (b) Slightly higher than that when the thunderstorm is not there: Incorrect, as thunderstorm activity lowers the pH. - (c) Uninfluenced by occurrence of thunderstorm: Incorrect, pH is affected by thunderstorms. - (d) Which depends on the amount of dust in air: Irrelevant, as dust does not have a significant role here.

Choosing the Correct Answer

Based on our analysis, choice (a) 'Slightly lower than that of rain water without thunderstorm' is the correct answer because thunderstorms create conditions for more acidic rain.

Key concepts

pH of Rainwater

The pH of rainwater is a measure of its acidity or basicity. Pure water has a neutral pH of 7. However, rainwater is naturally slightly acidic, usually with a pH around 5.6. This acidity comes from the presence of carbon dioxide in the atmosphere, which dissolves in rainwater and forms carbonic acid. When acid rain forms, the pH can drop even lower due to additional acidic components. Higher acidity poses challenges for the environment, affecting soil, waterways, and plant life. Regular monitoring of rainwater pH helps in understanding the impacts of pollution and climatic effects.

Nitrogen Oxides

Nitrogen oxides are pollutants produced mainly from combustion processes. They include gases such as nitrogen dioxide (\( \text{NO}_2 \)) and nitric oxide (\( \text{NO} \)). These gases react with other substances in the atmosphere and contribute to air pollution problems like smog and acid rain.
• Nitrogen oxides are harmful to the respiratory system and can exacerbate asthma conditions.
• These oxides can travel long distances in the atmosphere before falling to the ground as acid rain, affecting areas far from their source.
Understanding the formation and effects of nitrogen oxides is crucial for managing air quality and reducing the negative impacts on the environment.

Thunderstorm Effects

Thunderstorms have both electrical and chemical impacts on the atmosphere. Lightning, a key feature of thunderstorms, can initiate chemical reactions in the atmosphere. This electrical energy causes nitrogen and oxygen to combine and form nitrogen oxides.
When these oxides dissolve in rainwater, they form nitric acid, leading to lower pH levels and more acidic rain.
• Thunderstorms can thus increase the acidity of rainwater temporarily.
• These effects are generally localized around the areas where thunderstorms occur but can have significant environmental impacts.
The study of thunderstorms and their effects on rainwater is important for understanding weather patterns and protecting ecosystems from potential acidification.

Rainwater Composition

Rainwater is composed largely of water, but it also contains dissolved gases and particles from the atmosphere. Typical components include nitrogen, oxygen, carbon dioxide, and, due to pollution, substances like nitrogen oxides and sulfur dioxides.
• Dissolved gases: These are important as they influence the chemical quality and pH of the rainwater.
• Particulates: These can include dust, soot, and other micro-particles which may be washed out during rainfall.
The interaction of these components dictates the overall quality of rainwater and plays a key role in the formation of acid rain.
Understanding rainwater composition helps in assessing environmental impacts and addressing pollution control measures effectively.