Problem 57 - A Complete Resource Book in Chemistry for JEE Main

Question

Surface water contains (a) only salt (b) organic matter (c) salt and organic matter (d) suspended impurity

Step-by-Step Solution

Answer

Surface water contains salt and organic matter (option c).

Step 1: Understand Surface Water

Surface water refers to any body of water found above ground, including rivers, lakes, and oceans. It plays a crucial role in the water cycle and is vital for ecosystems, human consumption, and agricultural activities.

Step 2: Identify Potential Components of Surface Water

Surface water can contain various components, including salts dissolved from the earth as water runs over and through ground materials, organic matter from decaying plants and animals, and suspended impurities such as soil or other particulate matter.

Step 3: Analyze Each Option

- Option (a), "only salt", is incorrect because while surface water may contain salts, it can also contain other constituents. - Option (b), "organic matter", is partially correct as it may be present, but surface water also includes minerals and other impurities. - Option (c), "salt and organic matter", includes both salts and organic matter, making it more comprehensive than each individually. - Option (d), "suspended impurity", is also present but doesn't account for the dissolved salts or organic matter.

Step 4: Choose the Best Answer

The most comprehensive answer, which includes both salts and organic matter commonly found in surface water, is option (c) "salt and organic matter". This option accounts for the primary dissolved and particulate constituents in surface water.

Key Concepts

Organic Matter in Water

Surface water is often rich in organic matter. This includes materials that derive from living organisms, such as plants and animals. Organic matter in water largely consists of compounds like proteins, fats, carbohydrates, and even certain hormones. These materials can be released from decaying plant and animal material.

In terms of impact, organic matter is crucial because it serves as a nutrient source for aquatic life. However, too much organic material can lead to problems. For example, it can reduce oxygen levels in water when bacteria decompose it. Understanding the balance of organic matter is key to maintaining healthy aquatic ecosystems.

Dissolved Salts

When we talk about salts in water, we refer to dissolved ions that result from various chemical reactions as water travels through rocks and soils. The primary ions in surface waters include calcium (\(Ca^{2+}\)), sodium (\(Na^{+}\)), magnesium (\(Mg^{2+}\)), and chloride (\(Cl^{-}\)).

• These ions contribute to the water’s salinity and conductivity.
• They are important for aquatic life, impacting habitats and biological processes.
• Salts influence water quality and usability, particularly for drinking and agriculture.

Understanding dissolved salts and their concentrations is essential for environmental chemistry, as it affects both ecosystem health and human use.

Suspended Impurities

Suspended impurities in water include a variety of non-dissolved particles that are carried along by flowing water. These particles can be either organic, like algal cells, or inorganic, such as silt or sand. Suspended impurities affect the water's clarity and can influence the penetration of light, which is crucial for photosynthesis in aquatic environments.

• High levels of suspended impurities can reduce sunlight, affecting plant growth.
• They often indicate the health of a water body, with increased levels sometimes signaling pollution or erosion.
• Methods like sedimentation or filtration are typically used to remove these impurities from water.

Water Cycle Contributions

The water cycle plays a significant role in the composition of surface water. As water evaporates from oceans and other bodies of water, it leaves behind salts and pure water vapor forms clouds. This water eventually precipitates back to the surface in the form of rain or snow, replenishing surface waters with fresh inputs.

This continuous cycling helps regulate the concentration of dissolved substances and organic matter in surface waters. Rainfall can dilute higher concentrations of salts and impurities, whereas evaporation tends to increase salinity by removing only the water molecule. The water cycle is therefore crucial in maintaining ecological balance in surface waters.

Environmental Chemistry

Environmental chemistry involves studying the chemical and biochemical phenomena that occur in natural places. When it comes to surface water, it focuses on understanding the interactions between different chemical components such as organic matter, salts, and impurities.

• It aims to understand the distribution and effects of chemical species in the environment.
• Environmental chemists work to find ways to protect against pollution and contamination.
• The goal is to ensure both ecosystem health and safe human use of water.

This field is critical in developing strategies to manage and preserve water purity and regulate the impact of human activities on aquatic environments.