Download 10th Class Chemistry Notes (Unit # 15) for Federal Board (FBISE) Islamabad

Download 10th Class Chemistry Notes (Unit # 15) for Federal Board (FBISE) Islamabad.

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Download 10th Class Chemistry Notes for Federal Board (FBISE) Islamabad


Question: List the impurities present in rain water.
Rainwater contains pollutants, soil, plant parts, insect parts, bacteria, algae, and sometimes radioactive materials that the rain/snow has washed out of the air.

Question: List toxic substances pr sent in household wastes.
Household wastes include, human wastes, livestock wastes, soaps and detergents, paints and oil, food and vegetable wastes, garbage etc.

Question: In what ways, industrial wastes  pollute water.
Manufacturing of industrial products are always accompanied by some by­products and waste effluents.  These wastes may contain highly toxic compounds and heavy metals such as Pd; Cd, Cr. Hg, As, Sb etc. Water from leather tanr1eries contains large quantities of chromium (VI) salts. Chromium (VI) ions are highly toxic and known to cause cancer.

Question: What is water pollution?
Water  pollution  is the  contamination  of  water  bodies  (e.g.  lakes,  rivers, oceans, aquifers and groundwater). Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds.

Question: List some waterborne diseases.
  1. Cholera
  2. Dysentery
  3. Jaundice
  4. Typhoid
  5. Hepatitis
Question: What are pathogenic microorganisms?
An organism of microscopic size, usually a bacteria or virus, that causes disease.

Question: What  is hard  water? Why is it sometimes undesirable?
Water that gives little lather or forms scum with soap is called hard water.
Hard water  is undesirable:
  • Hard water with a lot of dissolved minerals usually calcium, does not work with soaps or detergents.
  • It is hard to "lather" with hard water, and you use more cleaning product to get the same effect. 
  • Second, the minerals can be deposited in pipes, fixtures and appliances, clogging or wearing them prematurely.

Question: What are the Earth's four main water sources?
The four main sources of water are, ground water, rivers or lakes, oceans and ice (glaciers).
Question: List two ways in which lakes and streams become polluted.
  • Industrial units generally discharge their wastes either to open land or into water bodies, lakes, ponds, rivers or oceans.
  • Water from leather tanneries contains large quantities of chromium (VI) salts. Chromium (VI) ions are highly toxic and known to cause cancer.
  • Industrial wastes cause irreversible degeneration of the environment causing serious health problems for public and marine life.

Question: Give chemical equations for the
a) reaction of slaked lime with alum.
3Ca (OH)2 + Al2 (SO4)3 ---------------> 2Al (OH)3 + 3CaSO4
b) carbonated rain water  with lime stone.
CaCO3 + H2CO3 ---------------> Ca(HCO3)2
c) reaction that occurs when temporary hard water  is boiled.
Ca(HCO3)2 ---------------> 2CaCO3 + CO2 + 2H2O
Mg (HCO3)2 ---------------> 2MgCO3 + CO2 + 2H2O
d) Ca+2  ions interact with  sodium zeolite
Ca+2 + Na2Z ---------------> 2Na+ + CaZ

Question: How can buildings made of limestone be affected by acid rain?
  • Acid  rain  has  a  corrosive  effect  on  limestone  or  marble  buildings  or sculptures. It is well established that either wet or dry deposition of sulfur dioxide significantly increases the rate of corrosion on limestone, sandstone, and marble.
  • Sulfur dioxide plus water makes sulfurous acid. Therefore buildings made of limestone are affected by acid rain.

Question: List some disadvantages  of water hardness.
  • Hard water wastes a lot of soap, when used for washing.
  • The soap forms scum with hard water, which adhere to the clothes being washed. Scum can spoil the finish of some fabrics.
  • Cause kettles to fur.
  • Can cause hot water pipes,  boilers  and car radiators  to block due to the formation of insoluble calcium and magnesium salts, causing great damage.

Question: What is the purpose of coagulation in water treatment?
It is the process in which water is treated with slaked lime and alum. These materials react to form a gelatinous mass of aluminum hydroxide.
3Ca (OH)2 + Al2 (SO4)3 ------------> 2Al (OH)3 + 3CaSO4
The aluminum hydroxide carries down dirt particles and bacteria.

Question: Explain how hard water hampers the cleansing action of soap.
  • Unfortunately, hardness minerals (calcium or magnesium ions) combine with soap to form an insoluble "curd... which can remain as a residue on washed laundry.
  • This is similar to the difficult-to-clean residue found on bathroom tubs, sinks, and tile in hard water areas.
  • Hardness  also  tends  to  counteract  soap's  alkalinity,  which  reduces  its  cleaning ability and requires the use of greater quantities to get laundry clean.

Question: Why is it cooler near a lake than inland during summer?
Since rate of evaporation increases with the increase in temperature during summer. Since evaporation cause cooling therefore it is cooler near a lake than inland during summer.   
(Rate of evaporation α temperature)

Question: How  chemistry helps maintain a dean swimming pool?
Water  in swimming pools is purified from pathogenic organisms by aeration and  chlorination.  Chlorination is a probably the  best and the  cheapest  method  of sterilization of water and it is the most effective in  destroying pathogenic bacteria. For  chlorination, liquid chlorine may be added directly in the swimming pool water.

Question: Why it is advisable to  wash hands well with soap after using bathrooms?
If your  hands are  not  clean  and  you  touch your  face  or public surfaces, you may  be  infecting yourself and  others  by  spreading germs and  disease. Colds, flus, and   infectious  diarrhea  are   all   known  to   be   spread  by   hand-to-hand contact Washing your  hands  regularly can  help  keep  you  8nd  those around you  healthy by controlling the spread of germs (bacteria and viruses).

Question: Describe the properties of water.
  • Water exists in three different states on Earth. Solid, Liquid, Gas.
  • Pure water is transparent, colourless, odourless and tasteless.
  • It boils  at 100°C and freezes at 0°C at the sea level.                                                 
  • Water has a high heat capacity. 
  • Water has a high heat of vaporization.

Question: Water is remarkably versatile solvent. Justify the statement.
The ability of water to dissolve a wide variety of substances is due to its two properties, the polarity of water molecules and the ability of water molecules to form hydrogen bonds. Water molecules are strongly attracted to ions, polar molecules  with which water  can  form  hydrogen  bonds. 

Question: What is Scum?
It is difficult to make the soap lather in hard water. Instead, the water becomes cloudy. This cloudiness is due to the formation of a white precipitate by the reaction of Ca+2 or Mg+2 ions present in hard water and soap. This white precipitate is known as scum.

Question: How does hard water differ from soft water?
Soft water:
Water that easily gives lather with soap and does not form scum is called soft water.
Water that gives little lather or forms scum with soap is called hard water.
Question: How does hardness produced in water?
  • Rainwater dissolves carbon dioxide as it falls through the atmosphere.
  • Carbon dioxide reacts with water to produce carbonic acid, which is a weak acid.
CO2 + H2O <-----------------------> H2CO3
  • This carbonated water passes over or through the rocks containing calcium carbonate or magnesium carbonate, the acid present in it attacks these rocks. 
  • It slowly dissolves them, forming calcium and magnesium hydrogen  carbonates.
CaCO3 + H2CO3 -------------------> Ca(HCO3)2
MgCO3 + H2CO3 -------------------> Mg(HCO3)2

Question: Which water is soft, tap water or distilled water?
Tap water contains impurities (CaSO4, MgSO4) in the water that distilled water does not have. Therefore distilled water is a soft water.
Question: Have  you  ever  noticed that the  pan  which is  regularly used  for boiling water gets  white or  yellowish deposits at its bottom and sides?
This is due to the boiler scales of CaCO3 and MgCO3.

Question: Differentiate among temporary and permanent hard  water. OR Describe the types of hardness of water?
Hardness in water can be divided into two types, temporary and permanent. Temporary hardness:
Temporary hardness is so called because it can be removed by boiling.
Permanent hardness:
Permanent hardness is so called because it cannot be removed by boiling. Temporary hardness is caused by the presence of dissolved calcium or magnesium hydrogen carbonates. Whereas permanent hardness in caused by the presence of dissolved sulphates and chlorides of calcium or magnesium. Hard water hampers cleaning action of soap.

Question: How to overcome the problem of scum produced by hard water?
To overcome the problem of scum formation in hard water, detergents have been produced. Detergents do not produce a scum.  This is because they do not react   with calcium or magnesium ions present   in hard water.   Also detergent molecules are biodegradable. Bacteria can easily break these molecules, so they do not persists in the environment.

Question: Write names of six household wastes.
Household wastes include, human wastes, livestock wastes, soaps and detergents, paints and oil, food and vegetable wastes, garbage etc.

Question: Describe the occurrence of water?
  • Water is one of the most important  substances  on Earth.
  • It has been estimated  that  total  amount  of  water present  on earth is about 1.33 billion cubic kilometers which nearly covers 71% of the Earth's crust.
  • Fresh water available to man is only 0.2% of the total.
  • Sodium chloride is the most abundant salt in sea water. It is present up to 3.4% in it. This water is unfit for human use.

Question: Explain the composition of water? OR How can you split water?
  • Water is normally a poor conductor of electricity. However, when electricity is passed through acidified water in a voltammeter, water decomposes.  
  • It gives hydrogen and oxygen. The process is called electrolysis and the reaction can be written as
2H2O -------------------> 2H2 + O2
  • The splitting of water molecules produces double amount of hydrogen as compared to oxygen.
  • This means hydrogen and oxygen in water are in the ratio of 2:1 by volume.
  • Hydrogen is collected at cathode and oxygen is collected at anode.

Question: Highlight the importance of water in the environment including industry.
  • You can live without food for 3 to 4 weeks, but cannot survive without water for more than 3 or 4 days.
  • Water is crucial for sustaining the reactions that keep us alive. For instance digestion, distribution of food through blood, removal of waste matter from the body.
  • It cools automobile engines, nuclear power plants, steel mills and parts of heavy machinery in industrial units.
  • It provides means of transportation on the earth surface.
  • Farmers need a large amount of water for -their fields for growing fruits, vegetables and crops.
  • We need water for drinking, cooking and cleaning.
  • It is also used to generate electricity.

Question: What do you understand by water pollution? Describe the causes of water pollution?
  • The  fresh  water  we  drink  or  use  for  our  daily  life  processes is  a  dilute solution  containing a number  of minerals. 
  • When these minerals are in sufficient concentration, water becomes unfit for human use.
  • Many human activities also result in the contamination of the  surface  and ground  water.  Several forms of pollutants affect water bodies. 
  • The human activities such  as  house  hold  wastes,  agricultural wastes,  livestock  wastes,  pesticides,  oil leaks,  detergents,  septic  tanks,  petroleum;  natural  gas  production  may result  in contamination of water bodies.

Question: Describe the methods to remove temporary hardness?
i)      By Boiling:
Hardness of water can be removed simply by boiling.   During   boiling   the soluble   calcium   and magnesium hydrogen carbonates are decomposed forming insoluble carbonates. Since Ca+2 and Mg+2 ions are removed as insoluble carbonates, water becomes soft.
M (HCO3)2 ------------------> MCO3 + CO2 + H2O
Where M = Ca+2 or Mg+2
ii)     By adding slaked lime (Clark's method):
Temporary hardness in water on the large scale can be removed by adding an estimated amount of slaked lime in it. The slaked lime reacts with the hydrogen carbonates to form insoluble carbonates.
Ca (HCO3)2 + Ca (OH)2 -----------------> 2CaCO3 + 2H2O
Mg (HCO3)2 + Ca (OH)2 ---------------> CaCO3 + MgCO3 + 2H2O

Question: Describe the methods to remove permanent hardness?
i)       By adding washing soda:
On the large scale permanent hardness in water can be removed by adding washing soda (Na2CO3.1OH2O).  Ca+2 and Mg+2 ions are removed as their insoluble carbonates.
M+2 + CO3-2 -----------------> MCO3
Where M = Ca+2 ,  Mg+2
ii)     By ion Exchange Resins:
The  hard  water  is  passed  through  a container  filled  with  a suitable  resin containing sodium  ions. Zeolite is one of the natural ion exchanger. Chemically it is sodium   aluminum silicate.   It is usually written as Na2Z.  The Ca+2 or Mg+2 ions causing the hardness are exchanged with Na+ ions in the resin.

M+2 + Na2Z ----------------> 2Na+ + MZ
Where M+2 = Ca+2 , Mg+2

The  used   up  zeolite   can  be  regenerated  by  heating   with  concentrated solution  of NaCl. This makes the process economical
CaZ + 2NaCl -------------------->  Na2Z + CaCl2

Question: Describe the various types of waterborne diseases.
Unclean water supplies, poor sanitation and poor hygiene kill 2,668,000 people worldwide each year. Water in swimming pools is purified from pathogenic  organisms  by aeration and chlorination.
Some waterborne diseases are given below.
i.       Cholera:
Cholera  is  an intestinal  disease.  It is caused by bacteria such as vibrio cholerae, E.coli etc.  Which may be present in water contaminated with human wastes. It is characterized by vomiting and purging.
ii.      Dysentery:
Dysentery is also an intestinal disease. It is caused by parasite, Entamoeba. This infection is transmitted by faecal contamination of water or food by en-cysted organism. Patients have mild to severe abdominal cramps, diarrhea, chocolate coloured stool with mucous and sometimes with blood.
iii.     Jaundice:
This disease  proceeds  from obstruction of liver. Excess  of bile from the liver enters  in  the  blood  and causes  yellowness of  skin  and  eyes.  It leads to loss of appetite, weakness and fatigue
iv.     Hepatitis:
Hepatitis is acute inflammation of liver. It is caused  by viruses,  and classified as Hepatitis  A, B, C, D and E. Hepatitis  A and E spreads  through  polluted water.
v.      Typhoid:
Typhoid is a dangerous   intestinal disease.   It spreads by polluted water containing bacteria such as salmonella typhi, salmonella paratyphi, and salmonella enteritidis.   It  is  characterized by  continuous fever  between 101oF  to  104oF   and irregular  pulse.

Question: How raw water is treated.
The raw water is treated in a municipal water purification plant, to make it fit for drinking and domestic purposes. Various stages in this treatment are;
1.      Sedimentation:
It is the process in which water is allowed to stand in a reservoir.. The suspended matter sinks to the bottom.
2.      Coagulation:
It is the process in which water is treated with slaked lime and alum. These materials react to form a gelatinous mass of aluminum hydroxide.
3Ca(OH)2 + Al2(SO4)3 ----------------->  2Al(OH)3 + 3CaSO4
The aluminum hydroxide carries down dirt particles and bacteria.
3.      Filtration:
The water is then filtered through sand and gravel.  Sometimes it is filtered through charcoal to remove coloured and odorous compounds.
4.        Chlorination:
In the final step, chlorine is added to kill any remaining bacteria. Chlorine reacs with water to form hypochlorous acid HClO which kills bacteria.
Cl2 + H2O ----------------> HClO + H+ + Cl-




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Download Class Notes: Download 10th Class Chemistry Notes (Unit # 15) for Federal Board (FBISE) Islamabad
Download 10th Class Chemistry Notes (Unit # 15) for Federal Board (FBISE) Islamabad
Download 10th Class Chemistry Notes (Unit # 15) for Federal Board (FBISE) Islamabad
Download Class Notes
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