KPK Class 10 Chemistry Notes Chapter #15 | (Environmental Chemistry II: Water)

Short Questions and long questions (Environmental Chemistry II: Water) KPK Class 10 Chemistry Notes Chapter #15. We have uploaded complete and comprehensive notes of Chapter #15 for all kpk boards.

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Class 10 Chemistry Notes Chapter #15

Chemistry Chapter 15 short questions for the Students of 10th Class kpk textbook boards. All of these Chemistry Chapter 15 notes are helpful for kpk Board students.

Q.1) Identify the factors which are responsible for dissolving polar substances in the water? 

Answer: 
The water molecule has a polar structure. The hydrogen on one end of the water molecule is partially positive (H+𝛿) while the oxygen n the other end is partially negative (O-𝛿). Because of this polar structure, water is an excellent solvent for ionic salts, mineral acids, and bases. Polar substances dissolve in water by the ion-dipole force of attraction between ion and water molecules. When a polar compound is added into water, oppositely charged ions are surrounded by water molecules. These oppositely charged ions of polar compounds are pulled by the water molecules and it becomes soluble in water. For example, NaCl, KCl, Na2CO3, etc. are soluble in water.

Read more: KPK Class 10 Chemistry Notes Chapter #14

Q.2) Explain why it is advisable to drink boiled water. 

Answer: 
The water might appear clean but it may contain unsafe microorganisms, like bacteria, which can cause different diseases i.e. diarrhea, typhoid. Boiling water is an efficient method of purification. Water boils at 100 °C or 212 °F, most of the microorganisms do not survive at this temperature. So, boiling the water makes it safe for drinking by killing biological contaminations i.e. bacteria and viruses.
Boiling the water sterilizes it against pathogens, and make sure they get removed, or thoroughly devastated and inactive. Boiling kills bacteria, viruses, or protozoans that can cause disease. Boiling makes the tap water microbiologically safe. Therefore it is advisable to drink boiled water. In fact, boiling water is still a much better way of obtaining safe drinking water, even in contrast to modern methods like filtration or chemical treatments.

Q.3) Why ice floats on the surface of water?     

Answer: 
All solids and liquids expand when heated and shrink when cooled. The density of a substance increases with decrease in temperature. However, water presents an exception to this universal rule. Up to 4 °C, water behaves like other liquids i.e. when water is cooled from 100 °C to 4 °C, its density increases from 0.9584 g/cm3 to 1 g/cm3. Below 4 °C, the reverse happens and the density gradually decreases to 0.917 g/cm3 at 0 °C. The expansion of ice is due to the formation of hexagonal structures within water molecules at each vertex. In between the molecules is empty space. As a result volume of water in ice increases and density decreases. As a result, the density of ice at 0 °C is lower than the water. Therefore, ice floats on water because it is lighter than water.

Q.4) Explain the importance of water and its quality? 

Answer: 
Importance of water: Water is an important requirement for maintaining life. The reactions which take place in our body and keep us alive occur in the presence of water. It regulates the temperature of the earth. Water is a universal solvent as it dissolves many substances in it.
The unique quality of water: All solids and liquids expand when heated and shrink when cooled. The density of a substance increases with decrease in temperature. However, water shows a unique behavior in this regard. When water is cooled down below 4 °C its density decreases. At 0 °C, the density of water becomes 0.91 g/cm3. Thus ice is lighter and therefore floats on the surface of the water. The expansion of ice is due to the formation of hexagonal structures.

Q.5) What is eutrophication? How does it pollute water?     

Answer: 
Eutrophication:
Eutrophication is when water bodies become enriched with nutrients, typically compounds containing nitrogen, phosphorus, or both. Run-off from the agricultural fields where fertilizers and pesticides have been used enters into ponds, streams or rivers. This water contains nitrate (NO3) and phosphate (PO43-) salts. These salts cause rapid growth of algae, floating over the surface of the water. They prevent sunlight and oxygen to reach the aquatic plants and animals. These plants die and decay. As decaying plants are biodegradable, they consume the oxygen gas present in the water. Thus, the depletion of oxygen results in the death of aquatic life.

Read more: KPK Class 10 Chemistry Notes Chapter #13 (Biochemistry)

Q.6) How chemistry helps to maintain clean swimming pools?     

Answer: 
Chemistry helps to maintain a clean swimming pool by killing bacteria and other microorganisms by using Chlorine-based disinfectant. It can be easily applied, measured and controlled. It is fairly persistent and relatively cheap. Chlorine itself does not kill when it is added to water, but it reacts with water to form hypochlorous acid (HOCl) and hydrochloric acid (HCl).
Cl2(g) +H2O(l) ⟶ HOCl(aq) + HCl(aq)
The hypochlorous acid (HOCl) is unstable. It readily produces the atomic Oxygen (O), which can bleach the dyes and kill the germs by oxidation. Wet chlorine acts as both a bleaching agent and a germicide.
HOCl(aq) ⟶  HCl(aq)  + [O]
When the amount of Chlorine is increased in the swimming pool water, it can cause eye irritation. The minimum concentration of chlorine in the swimming pool water is 0.5 mg/dm3 and the maximum level is 1.5 mg/dm3.

Q.7) Make the distinction between the soft and hard water.     

Answer: 
Soft water is that water, which easily produces good lather and does not scum with soap. While hard water is that water, which produces little lather and forms scum with soap. In other words, the water which produces curds with soap. It will not form lather with soap and dirt cannot be removed readily. Thus hard water wastes soap and effects the cleaning action of soap.

Q.8) Why water is universal solvent? 

Answer: 
Water is the best-known solvent. It can dissolve more substances than any other solvent. Due to this fact, it is termed as a universal solvent for many inorganic and certain compounds. This characteristic property of water that it dissolves more or less of everything is due to the following properties reasons:
(i) Polarity of water molecules
(ii) Hydrogen bonding in water
(iii) Dielectric constant

Q.9) Give some of the disadvantages of the detergents? 

Answer: 
Following are the major disadvantage of detergent over soap:
(i) Detergents are non-biodegradable. Microorganism like bacteria cannot decompose detergent, while these microorganisms can easily decompose soap.
(ii) Household water containing these detergents when discharged in lakes and rivers, cause water pollution. They produce stable foams in the rivers and pose a danger to aquatic life.
(iii) The phosphate salts present in detergents cause rapid growth of algae in the water. These plants die and decay by consuming oxygen gas present in the water. Thus, the depletion of oxygen results in the death of aquatic life.

Q.10) Identify the different toxic substances in household wastes. 

Answer: 
Household wastewater consists of water used in the kitchen, washrooms and cleaning floors, etc. The water discharged includes detergents and other chemicals like medicines, acids, bleaches, dyes, waxes, hair colors, etc., which affect water quality and affect the aquatic life. Solid waste also called urban waste/domestic waste contains food, glass bottles, cans, metals, etc.

Read more: KPK Class 10 Chemistry Notes Chapter #12 (Hydrocarbons)


Long Questions Chemistry Class 10 Notes Chapter #15

Class 10 Chemistry Notes Chapter #15 with ease
KPK Class 10 Chemistry Notes Chapter #15 | (Environmental Chemistry II: Water)

Q.1) (a) Enlist the main sources of water. 

Answer: 
The main sources of water are:
1. Oceans
2. Glaciers
3. Ice caps
4. Underground water
5. Inland water (rivers, lakes, canals, streams & soil moisture)

Q.1) (b) How would you categorize physical properties of water?

Answer: 
Physical properties of water:
1. Pure is colorless, odourless and a tasteless liquid. The taste of water is due to the dissolved salts and gases.
2. Water exists in nature in all three states i.e. solid (ice), liquid and gas (vapours).
3. Freezing point of water is 0 °C and boiling point is 100 °C.
4. Pure water is neutral to litmus. It does not change the colour of the litmus.
5. Pure water has minimal electric conductivity, but it’s conductivity increases as electrolyte (salt) dissolved in it.
6. Water is a polar molecule.
7. Pure water has density of 1.0 g/cm3 at 4 °C.
8. It has heat capacity pf 4.18 J/g °C.
9. Water conducts heat more easily than any other liquid.
10. Water has high surface tension.
11. The latent heat of fusion of water is 6 kJ/mole, while the latent heat of vaporization of water is 41 kJ/mole at 100 °C.

Q.1) (c) Predict the product of reaction,

 (i). K       (ii). Cl2         (iii). CaO         (iv). CH3COONa                 (v). C,  with water. 

Answer: 
(i). K       
Potassium (K) reacts with cold water forming potassium hydroxide (KOH), and produce Hydrogen gas.
2K(s)    +   2H2O(l)    ⟶     2KOH(aq)  +   H2(g)
(ii). Cl2         
Chlorine gas reacts with water to produce hydrochloric acid (HCl) and hypochlorous acid (HOCl). The hypochlorous acid (HOCl) is unstable. It readily produces the atomic Oxygen (O), which can decolourise and kill the germs by oxidation. Wet chlorine act as both a bleaching agent and a germicide.
Cl2(g) + H2O(l) ⟶ HCl(aq) + HOCl(aq)
HOCl(aq) ⟶ HCl(aq) + [O]
(iii). CaO         
Water reacts with calcium oxide (quicklime) forming calcium hydroxide (slaked lime).
CaO(s)  + H2O(l) ⟶ Ca(OH)2(aq)
(iv). CH3COONa        
Sodium acetate is a salt of a weak acid (CH3COOH) and strong base (NaOH) on reacting with water it undergoes hydrolysis and give CH3COOH acid and NaOH base.
CH3COONa(aq)+ H2O(l) ⟶ CH3COOH(aq) + NaOH(aq)
(v). C
When steam ispassed over a red-hot Carbon, a mixture of hydrogen and Carbon monoxide, known as water gas is produced.
C(s) (red hot carbon) + H2O(g)    ⟶    {CO(s) + H2(g)} water gas

Read more: KPK Class 10 Chemistry Notes Chapter 11 (Organic Chemistry)

Q.2) Water is an excellent solvent. Explain how this property is beneficial for life but sometimes harmful for us. 

Answer: 
Water is a universal solvent. It is able to dissolve a large number of substances. This property finds many applications in the home and industry. But the same property is the cause of water pollution as well.
Advantages of water as a Universal Solvent
Water can dissolve more substances than any other liquid. This serves an important role in living things on earth. This property of water allows for the transport of nutrients vital to life in animals and plants. When water goes through the air, the ground, or through our bodies, it takes along valuable chemicals, minerals, and nutrients. The solvent property of water has the following benefits:
(i) In living organisms: Water transports nutrients to the cells metabolizes body fat and flushes toxin out of the organs. The kidneys are responsible for filtering out unwanted substances from our bodies that come from the foods and drinks we consume. Kidneys then get rid of these substances after they get accumulated. Water being a great solvent dissolves these substances and sends them on the way out of our bodies.
(ii) In Plants: Plants absorb nutrients and water through their roots. Water helps in transporting minerals and nutrients throughout the bodies of plants through a process called vascular system.
(iii) In Industries: Water is majorly used in industries that produce metals, wood and paper products, gasoline and oils, chemicals, etc. In fact, every manufactured product uses water during some part of its production process. Industries can use water for washing, diluting, cooling, or transporting a product, etc.
(iv) In soft drinks and washing: Water is the major ingredient found in soft drinks. At homes, it is also used for washing purposes. It forms lather with detergents and soaps for cleaning.
Disadvantages of water as a Universal Solvent:
When natural water seeps through the surface of the earth, it dissolves salts and other minerals. This water is still considered fit for drinking. Water pollution occurs when undesirable substances enter natural water. These substances can be biological or chemical in nature. Most common pollutants are human and animal waste, radioactive material, toxic metals (e.g. mercury, lead, etc), fertilizers, agricultural chemicals, acid rain, etc. Water pollutants can be very harmful to humans, animals and water life. The effects can be devastating, depending on the nature of chemicals, concentrations of the pollutants and location they are polluting. Polluted water is neither suitable for drinking nor for use in agriculture and industry. Contaminated water is the cause of destruction and reduction of the reproductive ability of aquatic life. Most importantly, it is a hazard to human health. 

Q.3) (a) Classify temporary hard and permanent hard water. 

Answer: 
The hardness of water is classified as:
i) Temporary Hard Water                                          ii) Permanent Hard Water 
i) Temporary Hard Water:
The temporary hardness of water is due to the dissolved Calcium bicarbonate and Mangnesium bicarbonate. These salts are soluble in water and are present in the form of positive and negative ions as shown below
Ca(HCO3)2(aq) ⟶ Ca2+(aq) + 2HCO3(aq)
Mg(HCO3)2(aq) ⟶ Mg2+(aq) + 2HCO3(aq)
ii) Permanent Hard Water: 
The permanent hardness of water is due to the presence of Chloride (Cl) or Sulphate (SO42-) of Calcium and Magnesium i.e. MgCl2, MgCO3, and CaCl2. These salts are soluble in water and produce the respective ions in water. Simple boiling of the water cannot decompose these salts.
CaCl2(aq) ⟶ Ca2+(aq) + 2Cl(aq)
CaCl2(aq) ⟶ Mg2+(aq)  + 2Cl(aq)
CaCl2(aq) ⟶ Ca2+(aq) + SO42-(aq)
MgSO4(aq) ⟶ Mg2+(aq) + SO42-(aq)

Read more: KPK G10 Chemistry Notes Chapter-10 (Acids, Bases, Salts)

Q.3) (b) What methods could be adopted to remove the temporary hardness of the water. 

Answer: 
Methods for Removal of Temporary Hardness:
i. By Boiling the Temporary Hard Water
Temporary hardness of water can be easily removed by simple boiling the water. This hardness is caused by the presence of dissolved calcium bicarbonate, (Ca(HCO3)2, which decomposes on heating. The calcium carbonate (CaCO3) is formed. The calcium carbonate is insoluble and settles down as precipitate at the bottom.
Ca(HCO3)2(aq) ⟶ CaCO3(aq) + CO2(aq)  +  H2O(g)
ii. Clark’s Method
This method is used to remove the temporary hardness of water on a large scale. This is a chemical method. A calculated amount of slaked lime, [Ca(OH)2] is added to the temporary hard water. The soluble bicarbonate ions (HCO3) of calcium and magnesium present in temporary hard water are converted into their carbonate ions (CO3). The carbonates of calcium and magnesium are insoluble in water and settle down at the bottom.
Ca(HCO3)2(aq) + Ca(OH)2     ⟶ 2CaCO3(s) (white ppt.)  + 2H2O(l)
Mg(HCO3)2(aq) + Ca(OH)2     ⟶ 2MgCO3(aq) (white ppt.) + CaCO3(s) + 2H2O(l)

Q.3) (c) What methods could be adopted to remove the permanent hardness of water. 

Answer: 
Methods for Removal of Permanent Hardness:
Permanent hardness of water can only be removed by using chemicals, which convert soluble salts into insoluble salts on precipitation. The word permanent is misleading here because this hardness can be removed at the end
i. By Using Washing Soda:
The washing soda (Na2CO3) removes the permanent hardness of water. The washing soda reacts with the soluble calcium and magnesium chloride and sulphate and converts them into insoluble calcium and magnesium carbonate respectively.
Na2CO3(aq) + CaCl2(aq) ⟶ CaCO3(s)  + 2NaCl(aq)
Na2CO3(aq) + MgCl2(aq) ⟶ MgCO3(s)  + 2NaCl(aq)
Na2CO3(aq) + CaSO4(aq) ⟶ CaCO3(s)  + Na2SO4(aq)
Na2CO3(aq) + MgSO4(aq) ⟶ MgCO3(s)  + Na2SO4(aq)
ii. Ion Exchange Method:
Zeolite is an ion-exchange resin which is integral part in the water treatment process in both consumer and industrial settings. Zeolite is naturallyoccurring sodium aluminum silicates. It can also be prepared artificially. This resin is commonly known as Sodium Zeolite.
When the hard water is passed through the resin, the Sodium ions will go into the solution while the unwanted Calcium and Magnesium ions take their place in the resin.
CaSO4(aq) + Na2-Zeolite ⟶ Ca-Zeolite + Na2SO4(aq)
Soluble                                               Insoluble
MgSO4(aq) + Na2-Zeolite ⟶ Mg-Zeolite + Na2SO4(aq)
Soluble                                               Insoluble
When the Na2-Zeolite is used up and becomes inactive then it can be regenerated by treating it with a strong solution of common salt (NaCl).
Ca-Zeolite + 2NaCl(aq) ⟶ Na2-Zeolite + CaCl2(aq)

Q.4) (a) Why water is important for us? 

Answer: 
Water is an important requirement in our life. After air, the importance of water takes the second place for survival on earth. Earth is the only planet in the solar system that contains water. Living organisms consist of 50% to 80% water and every living organism requires water for its existence. Body organs need water to perform different bodily functions. It lubricates our food, keeps our organs moist and helps in digestion and movement of joints.
⦿ Water is vital for maintaining life. The reactions, which take place in our body and keep us alive occur in the presence of water.
⦿ Water regulates the temperature of earth.
⦿ Water serves as a medium for transportation, as ships and boats move on water.
⦿ Water is a universal solvent, as many substance dissolve in it.
⦿ Water enables our body to excrete waste during perspiration and urination. The kidneys and liver use it to help flush out these wastes from our body.
⦿ Water is used in cooking and washing.
⦿ Running water is used to generate electricity.
⦿ It is used in the radiators of automobiles engines to cool it. It is also used in nuclear power plants, steel and iron industries and other heavy industries.
⦿ Water in lakes, rivers and oceans are used as means of transportation.
⦿ Fish and other aquatic animals and many plants live in water.
⦿ Agriculture needs large amount of water, to cultivate fruits, vegetables, and other food.
⦿ It is required for irrigating crops, as seeds cannot germinate without water.
⦿ Many industries such as petroleum, fertilizer, dye and drugs industries require large quantities of water for various processes.

Q.4) (b) Write the disadvantages of hard water? 

Answer: 
Disadvantages of hard water:
The following are the disadvantages of hard water.
⦿ Hard water consumes a large amount of soap in the washing process.
⦿ Hard water is unfit to use in steam engine and boilers. When the hard water is used in the boiler, calcium and magnesium salts settles down at the bottom as a hard insulating scale. As a result, more fuel is consumed in producing steam. If these scales are not removed, they block the tubes, which lead to the engines. These make the constant threat to the explosion of the boiler. This deposition of scales in the boiler causes overheating and reduces the life of the boiler.
⦿ Use of hard water for drinking purposes for a long time causes dysentery, intestinal and stomach diseases. If magnesium sulphate is present in the hard water, it weakens the stomach function. 

Q.4) (c) Enlist the advantages of wastewater treatment? 

Answer: 
Advantages of wastewater treatment
1. Wastewater treatment process improves the quality of water for reuse.
2. In the treatment process, the removal of suspended and dissolved solids and killing of pathogens, like bacteria and viruses, makes the water clean and reusable. Waterborne diseases can be prevented through wastewater treatment.
3. The process also has the potential for the production of natural fertilizers that are used in agriculture to increase crops yield.
4. The process reduces waste production and produces energy by methane harvesting.

Read more: KPK G10 Chemistry Notes Chapter9 (Chemical Equilibrium)

Q.5) (a) How would you evaluate the effects of water pollution? 

Answer: 
Effects of water pollution
Water pollution has the following effects:
(i) It is hazardous to human health. People can get diseases such as hepatitis, cholera and diarrhea by drinking polluted water.
(ii) Polluted water kills life that depends on these water bodies. Dead fish, crabs, birds and sea gulls often wind up on beaches, killed by pollutants in their environment.
(iii) Pollution disrupts the natural food chain by damaging aquatic life. For example lead and cadmium are eaten by tiny animals. Later, these animals are eaten by fish and shellfish, and the food chain continues to be disrupted at all higher levels.
(iv) It causes rapid growth of algae. These plants die and decay causing deficiency of oxygen in water that results in death of aquatic life.
(v) It is unfit for cleaning or washing purposes.
(vi) It reduces the aesthetic quality of lakes and rivers.

Q.5) (b) Explain how industrial wastes pollute environment.

Answer: 
Industrial units are set up to produce the desired substances (chemicals, cloth, leather goods, rubber items, petrochemicals, and plastic items) on a large scale. These industrial units, unfortunately, discharge their wastes such as hot water, chemicals, and solid materials either to open grounds or to running water. These are absorbed by lower forms of life and passed into the food chain, causing deaths, birth defects, and mental problems. These substances are called industrial wastes.
⦿ Most of the industries have been started without proper planning and waste treatment plants. They just dispose off untreated toxic waste into nearby drains, canals or rivers. Industries produce lots of wastes. These wastes are highly toxic due to the presence of compounds like Mercury, Cadmium, Lead, Chromium, Arsenic, etc, acids such as hydrochloric acid (HCl), sulphuric acid (H2SO4), nitric acid (HNO3), etc, oils, grease, dyes and many also contain some gases in dissolved form.
⦿ Water used in industries as a coolant or for cleaning purposes dissolves all the chemicals and detergents and causes water pollution when discharged from industries. These industrial wastes also pollute groundwater. The compounds which are discharged from industries get into the body through edible substances and causes different diseases.
⦿ Radioactive wastes that may leak from nuclear power stations also creates many problems to the living organisms.
Heated Water: Some industries and power stations use water for cooling purposes. When this hot water discharges into the rivers. It may destroy the fish and other aquatic life if the temperature of this hot water is higher than 30 C.
Untreated Water: In areas where there are no sewage water treatment plants. The sewage water goes into rivers and other water sources. Sewage water consists of bacteria, germs, and viruses. When this water is used for drinking purposes, they cause Typhoid, Cholera, Hepatitis, Pneumonia and dysentery problems.

Q.5) (c) Support the view that domestic wastes cause pollution. 

Answer: 
Solid household waste also called urban waste or domestic waste is either in solid or semi-solid form. It contains food, glass bottles, cans, metals, etc. Today many people dump their garbage into streams, lakes, rivers, and seas. When rainwater or other forms of water come in contact with these materials (Chemicals), it removes or extracts chemicals from these wastes and these chemicals seep into the soil and pollutes underground water or finds its way to rivers and streams through rainwater. Water used in kitchens, washrooms and cleaning floors, etc. The discharged water contains detergents and other chemicals like medicines, acids, bleaches, dyes, waxes, hair colors affect aquatic life. Flushed water contains pathogens such as bacteria, viruses, and protozoans. When got mix with drinking water causes waterborne diseases.

Q.5) (d) How would you relate the agricultural wastes and water pollution. 

Answer: 
Agricultural wastes are wastes produced as a result of various agricultural activities. Agricultural wastes include both natural (organic) and synthetic wastes. Natural (organic) wastes include manure and other wastes from farming, harvesting, poultry and slaughter houses etc. Whereas, synthetic wastes consists of fertilizers in run-off water from fields, pesticides, insecticides and herbicides that enter into water, air or soils and salt and silt drained from fields. 

Read more: List of Chemistry Class 9 Notes All Chapters 2021 | all boards

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