Unit 20: Water — Short Questions

Methods used to check purity of water are:
i. Determining boiling point of water at STP
ii. Determining freezing point of water at STP

Tap water

• Water which is supplied to our homes, shops and offices through pipes is called tap water
• Tap water may contain minerals, chlorine, ions salt mixed with it.
• It has pH value 6.5 – 8.5
• It can conduct electricity.

Distilled water

• Water obtained after the process of distillation is called distilled water
• Distilled water is free from all minerals, ions salt and other impurities.
• Its pH is 7
• It is bad conductor of electricity

Distillation of water In a distillation flask water is taken. It is fitted with a long condenser. Water is boiled in distillation flask. The steam produced during boiling travels through condenser where it is cooled down. The condensed water (distilled) is collected in a separate container. Impurities like salts, minerals and other contaminants stay behind. In this way distillation is done in laboratory.

Useful substances in water Dissolved oxygen from atmosphere and aquatic plants.

Harmful substances in water

• Plastics: Microplastics
• Nitrates and phosphates through weathering of socks.

Harmful bacteria and other microbes present in water can be mostly removed by boiling as boiling kills most microbes.

Chlorination Chlorine disinfects water effectively and remove bacteria and other microbes.

Sedimentation

• Insoluble impurities which are bigger and heavier are often removed by the process called sedimentation.
• Heavier particles settle due to gravity.

Filtration

• This process is used to remove suspended particles of smaller size which are generally not removed in sedimentation process.
• Water passes through a filters (like sand or membrane) that traps particles to be removed.

Water – borne diseases Water borne diseases include.

• Cholera
• Typhoid
• Malaria

Nitrogenous fertilizers Nitrogenous fertilizers are added into the soil because it is required during the early stage of plant growth for the development of stem and leaves. It is the main constituent of proteins and imparts green color to the leaves and increase the yield and quality of plants.

Trachoma It is a disease caused by drinking contaminated water. It is particularly prevalent among babies and children in the developing countries. This disease causes blindness.

Presence of water Identifying the presence of water has many important applications which include determining the purity of substance and analysing chemical reactions. It is important for food and pharmaceutical industries where the presence of water can affect.

Test for water Hydrated copper(II) sulphate (CuSO₄. 5H₂O) is blue in colour but when it is heated, it loses water molecules to become anhydrous copper(II) sulphate which is white in colour. A drop of water on anhydrous sample of copper(II) sulphate changes its colour from white to blue.

CuSO₄ + 5H₂O ⟶ CuSO₄ .5H₂O
White Blue

It is a very sensitive test and can detect even a small amount of water.

Pure water boils at 100°C and freezing at 0°C under standard conditions of temperature and pressure. The impurities present in water will change both these physical constant.

• The presence of impurities will slightly increase its boiling point.
• Similarly, a melting point below 0°C suggests the presence of impurities in the sample of water

The purity of distilled water makes it ideal for use in the laboratories and medical procedures. It is also frequently used in pharmaceutical industry. Its purity ensures accurate scientific measurements sterilization of medical equipments and to prevent corrosion.

Tap water is a conductor of electricity due to the presence of free ions from dissolved minerals. Distilled water is free from ions, therefore it is a bad conductor of electricity.

Dissolved oxygen Dissolved oxygen is the useful gas in water. It enters the natural water from the atmosphere through the process of diffusion. It is also produced by aquatic plants and algae in the process called photosynthesis.

Purpose The absorbed oxygen is used by the aquatic organisms to breath and survive. It is responsible to maintain the health and diversity of ecosystem.

Harmful microorganism like bacteria viruses and parasites enter into natural water through human and animal waste, landfills, agricultural runoff and industrial effluents. Similarly, sewage from wastewater treatment plants or from faulty septic tanks can release pathogens directly into nearby water body.

Heavy metals and their compounds: Heavy metals (Pb, Hg and Cd etc.) can enter in natural water through many routes.

• Waste water from factories
• Mining operations
• Use of fertilizers and pesticides

Heavy metals and their compounds not only damage vital organs like liver and kidney, they can also lead to neurological problems. Arsenic and cadmium are known to increase the risk of certain cancers.

Harmful effects of plastics Very small particles of plastics called microplastics. It has been found in some human organs like lungs and blood. These particles can disturb the immune and reproductive system.

Eutrophication Eutrophication is the name of the process which starts in a water body containing excess of phosphorous and nitrogen nutrients.

Three types of impurities are mostly present in water obtained from natural sources.

(i) Dissolved impurities
(ii) Suspended impurities
(iii) Microorganisms

Insoluble impurities present in water include soil, pieces of plants and other organic matter and sand. These impurities are bigger in size and are often removed by the process called sedimentation.

Diagram showing a sedimentation tank with inlet on the left, outlet on the right, and sludge extracted from the bottom.

Filtration removes smaller suspended particles from water by passing it through a layer of sand and gravel filters that trape these solid particles. Clear water is removed as filtrate.

Water must be sterilized before humans can use it. All harmful bacteria and other microbes must be killed. For this purpose, a small amount of liquid chlorine is added which has the power to kill all these germs.

Water is passed through powdered activated carbon in the form of charcoal to remove taste and odour. It removes a wide range of organic compounds responsible for taste and odour through absorption.

The world Health Organization (WHO) has estimated that 80% of the sickness and diseases in the world are caused by polluted water and lack of sanitation. In all nearly 500 million people suffer from water borne diseases every year in the world.

Water-borne diseases can be avoided if we strictly follow the following instructions.

(i) Drink clean water after removing impurities and boiling to kill the germs.
(ii) Practice hygiene by keeping your body especially hands clean. Ensure proper sanitation facilities are available

Pakistan is included in a semi – arid region and hence receive a low rainfall annually. Northern Pakistan including Punjab generally receives rainfall within the range 250 – 600 mm per year during monsoon season. In southern Pakistan precipitation is scarce below 200 mm per year.

Micro – nutrients The nutrients which are required in a very small amount for the growth of plants are called micro - nutrients or trace - elements.

Examples Boron, Copper, iron, manganese zinc, molybdenum and chlorine etc

Range Their range is form 6 grams to 200 grams per acre

They are essential in small amounts because excess amounts are poisonous.

Macro-nutrients The nutrients which are required in a large amount for the growth of plants are called macro - nutrients.

Example Nitrogen, Phosphorous, Potassium, Calcium, magnesium, sulphur, carbon, hydrogen and oxygen.

Range There are generally required in range from 5 kg to 200 kg per acre.

Fertilizers are classified according to the nature of the elements like nitrogen, phosphorous and potassium which they provide to the soil.

This classification gives the following types of fertilizers.

(i) Nitrogenous fertilizers
(ii) Phosphatic fertilizers
(iii) Potassium fertilizers

Phosphatic fertilizers These fertilizers provide phosphorus to the plants or soil.

• Phosphorus is essential for plants because phosphorus is required to stimulate early growth.
• To accelerate the seed and fruit formation during the later stages of growth.
• It also increases resistance to diseases.

Potassium fertilizers These fertilizers provide potassium to the plant or soil.

• It is essential for plants because potassium is required for the formation of starch, sugar and the fibrous material of the plants.
• They increase resistance to diseases and make the plants strong by helping in healthy root development.
• They also help in ripening of seeds, fruits and cereals.

Plastic waste pollutes land, river and oceans.

• Micro plastics enter the food chain and affects ecosystem.
• Burning plastics is also a serious problem as it is regarded non – biodegradable.
• Plastic tiny particles (micro plastics) have been found in some human organs like lungs and blood. These particles can disturb the immune and reproductive systems.
• Plastics in soil reduces fertility and effects plant growth.

Distillation Distillation is a process that separates pure water from dissolved (soluble) impurities such as salt, sugar or minerals.

Process The process involves heating water to get steam and then condensing this steam back into liquid water by cooling. This process effectively removes all the dissolved minerals and contaminants from water leaving behind only pure water.

Urea as a good nitrogenous fertilizer urea is regarded as a good fertilizer because it is rich in nitrogen which is an essential nutrient for plant growth.

• High nitrogen content: Urea contains about 46% nitrogen which is higher than most of the nitrogenous fertilizers.
• Easily available to plants: When added to soil it is converted by soil bacteria into ammonium and then nitrates which are easily absorbed by plants.
• Urea is highly soluble in water

Water scarcity in Pakistan Pakistan is facing a severe water shortage due to a combination of natural, environmental and human factors.

Some of the factors are:

(i) Low and uneven rainfall:
Pakistan is included in a semi-arid region Northern Pakistan including Punjab generally receives 250 – 600 mm per year mostly during monsoon season. In southern Pakistan precipitation is scarce below 200 mm per year

(ii) Climatic change and melting glaciers:
Climatic change is causing glaciers to melt faster changing river flow patterns.

(iii) Rapid population growth:
Pakistan's population has been rapidly increasing raising the demand for water

(iv) Lack of storage facilities:
Pakistan has limited water storage capacity although there are major dams like Tarbela dam and Mangla dam store water but cannot store enough water to avoid shortage of water

See Q.5 from theory.

See Q.7 from theory.

See Q.10 from theory.

See Q.11, 12 from theory.

See Q.6 from theory.