Environmental Chemistry-Water

Some harmful substances in water:

  • Some metal compounds that are toxic
  • Some plastics that harm aquatic life
  • Sewage that contains harmful microbes which cause disease
  • Hitrates and phosphates that lead to de exygenation of water and damage to aquatic life. Details of the eutrophication process are not required)

Explain the treatment of domestic water supply (some examples include:

  • Sedimentation and filtration to remove solids
  • Chlorination to kill microbes
  • Use of carben to remove tastes and colours

Describe various water-borne diseases and the steps that can be taken to avoid them.

Identify the negative effects of water pollutants on life and the ways to avoid them.

Explain water scarcity as an important issue faced by Pakistan and the ways in which can be resolved.

Fertilizers:

State that urea, ammonium salts, and nitrates are used as fertilizers.

Explain the use of NPK fertilizers to provide the elements nitrogen, phosphorous, and potassium for improved plant growth.

INTRODUCTION

Where does the water in your kitchen and bathroom come from? Because water comes from different sources, its quality varies. Do you drink water that has a colour, a bad taste or an unpleasant smell? When you wake up in the morning, what do you do? You brush your teeth, take a shower, flush the toilet, etc. What happens to the water flowing out of the drain? Can you reuse this water? Sewage is often poured into open gutters and allowed to flow directly into streams, rivers and oceans. This practice spreads diseases and also threatens aquatic life. How? This will become clear in this chapter. The presence of disease-causing bacteria affects water quality. Water from both public and private sources often requires treatment to ensure it is clean and safe to drink. Wastewater should also undergo treatment to remove unwanted substances before entering lakes, rivers or oceans. Otherwise, it would also affect marine life and, through the food chain, humans.

12.1 PROPERTIES OF WATER

Water is the only substance that exists in three different states on Earth. Can you name these states?

Pure water is transparent, colourless, odourless and tasteless. It boils at 100°Cand freezes at O"C at the sea level.

Activity 12.1

Detection of water with anhydrous (II) copper sulphate

Objective:

The objective of this activity is to demonstrate the ability of anhydrous copper(II) sulphate to detect the presence of water by observing its reaction and colour change.

Materials Required:

Anhydrous copper (II) sulphate (in powder form), a dry test tube or small beaker, a pipette or pipette, spatula.

Procedure:

  1. Take a small amount of anhydrous copper (II) sulphate powder with spatula and place it in a dry test tube or beaker.
  2. Observe the initial state and the appearance of anhydrous copper(II) sulphate powder before adding water. It should be a white or off-white crystalline.
  3. Carefully add a few drops of water to the anhydrous copper(II) sulphate powder in the container using a dropper or pipette.
  4. Observe the reaction. When water comes into contact with anhydrous copper(II) sulphate, a chemical reaction occurs in it. Copper(II) sulphate reacts with water to form hydrated copper(II) sulphate, which is blue in colour.
  5. Observe and note the colour change that occurs. A white anhydrous copper (II) sulphate powder should turn light blue when reacted with water. This colour change confirms the presence of water.

Interpretation of results:

Anhydrous copper(II) sulphate is a white crystalline solid. It does not contain water molecules. However, it has ability to absorb water from the surrounding environment through a process called hydration. When water is added to anhydrous copper(II) sulphate, it undergoes chemical reaction. It reacts with water forming hydrated copper (II) sulphate, which has a distinct blue colour. The appearance of blue colour indicates the presence of water in it.

Safety Precautions:

Copper sulphate is a toxic compound, so handle it carefully. Perform this activity under the adult supervision. Wear gloves and safety goggles, and wash your hands, when the activity is over.

Activity 12.2

Testing the purity of water by determining its melting point.

Materials needed:

beaker, thermometer, bunsen burner or spirit lamp, ice cubes, tripod stand.

Procedure:

  1. Make ice cubes of sample water using refrigerator.
  2. Fill the glass with ice cubes.
  3. Hang the thermometer on the ice cubes, making sure that its bulb is completely

Chemistry - Water

Unit 12: Envi

Immersed in ice and does not touch the bottom of the beaker.

place the beaker on the heat source using the stand.

  1. Gradually heat the ice cubes,
  2. Record the temperature at which the ice begins to melt.

Record your observations,

Interpretation of results:

The melting point of pure water is O°C. Impurities in water affect its melting point. Compare the observed melting point with the expected value.

Activity 12.3

Testing the purity of water by determining its boiling point.

Materials needed:

beaker, thermometer, bunsen burner or spirit lamp, water sample, tripod stand, a glass rod.

Procedure:

  1. Fill the beaker with sample water and place it over the tripod stand.
  2. Hang the thermometer in the water, making sure that its bulb is completely submerged in water and does not touch the bottom of the beaker.
  3. Gradually heat water, constantly stirring water with a glass rod.
  4. Record the temperature at which the water begins to boil.
  5. Record your observations.

Interpretation of results:

The boiling point of pure water is 100°C. Impurities in water affect its boiling point. Compare the observed boiling point with the expected value.

12.1.1 Water as Solvent

Water is very good at dissolving substances. For this reason natural water such as rainwater and groundwater is not pure water. As water falls through the atmosphere, it dissolves, a little oxygen, nitrogen, carbon dioxide, and dust particies. During thunder storms, it also dissolves nitric acid. Ground water dissolves minerals from rocks and soils as it moves along on or beneath Earth's surface. Ground water also dissolves many substances from decaying plants and animals.

12.1.2 Quality of Water from Natural Resources

Water from natural resources such as lakes, streams, and underground rivers can contain many dissolved substances that can be beneficial or harmful.

12.1.3 Disadvantages of Natural Substances Found in Water:

  1. Dissolved oxygen: Where do fish and other marine life get their oxygen? Water contains dissolved oxygen. This oxygen is respomsible for the survival of aquatic organisms.
  2. Metal compounds: Natural water can contain metals such as iron, sodium, potassium, magnesium, calcium, manganese, zinc and copper. Some of these metals are necessary

for biological processes, their excessive concentration can be poisonous for aquatic organisms and humans.

  1. Plastics: Plastic waste can pollute water bodies. This is a serious threat to aquatic life and ecosystem.
  2. Wastewater: Wastewater can enter natural water supplies. Wastewater carries Wastewater ceste, viruses and other harmful substances. These pollutants pose a serious threat to humans and aquatic life.
  3. Harmful Microbes: Natural water sources can contain harmful microbes such as bacteria, viruses and parasites that can cause waterborne diseases such as diarrhea, dysentery, cholera and stomach upsets.
  4. Nitrates from fertilizers: Fertilizers add nitrates to water bodies through agricultural runoff. High concentrations of nitrates in drinking water cause health risks, especially for young children.
  5. Phosphates from fertilizers and detergents: Phosphates in fertilizers and detergents can enter water bodies through runoff. High concentrations of phosphate can cause eutrophication. This can cause harmful algae blooms and oxygen caps in water bodies. Detergents used in water systems can destroy the outer mucous membranes that protect fish from bacteria and parasites. In addition, detergents can also damage their gills.

12.1.4 Benefits of Natural Substances Found in Water:

Some naturally occurring substances are useful and necessary for life. For example,

  1. Dissolved oxygen: Existance of aquatic life depends on dissolved oxygen. This oxygen supports the respiration process of aquatic organisms.
  2. Essential minerais: Metal compounds in natural water can provide essential minerals needed for various biological processes. For example, iron is necessary for the production of hemoglobin in the blood, which carries oxygen to the cells of our body. Metals like zinc, copper, and manganese activate enzyme activity the proper functioning of biological systems.