Environmental Chemsitry II Water Punjab Class 10 Notes Unit 15 Pdf Download Short Question, Long Questions, Multiple choice questions and answers on environmental chemistry ii water.
Matric Notes Chemistry 10th Chapter 15 Environmental
How limestone dissolves in water?
Limestone (CaCO3) is basically insoluble in water. But it is readily dissolved by water that has become slightly acidic, usually from carbon dioxide in the air.
CaCO3 + CO2 + H2O → Ca(HCO3)2
The reaction produces hydrogen carbonate HCO3–Â ions, which are very soluble in water, and so the limestone dissolves.
What are the causes of hardness in water?
The hardness of water is because of dissolved calcium (Ca2+) and magnesium (Mg2+) ions. The rainwater while coming down absorbs carbon dioxide from the atmosphere. The water mixed with carbon dioxide when comes into contact with limestone and dolomite, converts insoluble carbonates of calcium and magnesium into soluble bicarbonates. It may also dissolve chlorides and sulphates of calcium and magnesium. These salts make the water hard.
CaCO3 + CO2 + H2O → Ca(HCO3)2
MgCO3 + CO2 + H2O → Mg(HCO3)2
What are the effects of temporary hardness in water?
The amount of minerals in water affects the amount of soap and detergent used for cleaning. Â Soap combines with the minerals of hard water to form sticky soap curd. Some synthetic detergents are less effective in hard water because the active ingredient is partially inactivated by hardness. When doing laundry in hard water, soap curds lodge in fabric and make it stiff and rough. Minerals can be deposited in pipes, fixtures and appliances, clogging them prematurely.
Mention the disadvantages of detergents.
Disadvantages of detergents
Many detergents are resistant to the action of microorganisms like bacteria and are not biodegradable.
i) Household water containing these detergents when discharged in lakes and rivers, cause water pollution.
ii) They produce stable foams in the rivers and pose a danger to aquatic life.
iii) The phosphate salts present in detergents cause the 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.
How do detergents make the water unfit for aquatic life?
As detergents are non-biodegradable, they remain in the water for a long time and make the water unfit for aquatic life. The phosphate salts present in detergents cause the 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.
Why are pesticides used?
Pesticides are used either directly to kill or control the growth of various pests and disease carriers, such as mosquitoes, rats and mice. Pesticides are used in agriculture to control weeds, insect infestation and diseases, which damage crops and transmit diseases both to humans and animals.
What are the reasons for waterborne diseases?
Water-borne diseases can be due to drinking water contaminated by human or animal faeces, which contain pathogenic microorganisms. Large poorly functioning municipal water distribution systems and toxins also contribute to the transmission of waterborne bacterial diseases.
How waterborne diseases can be prevented?
Waterborne diseases can be prevented by taking the following measures:
i) Ensuring that the drinking water is properly treated and purified.
ii) Keeping control over the use of pesticides and other chemicals.
iii) Not throwing or discharging the waste directly in waterways, streams or reservoirs.
How water rises in plants?
Water has the ability to flow in narrow spaces without the assistance of external forces and in opposition to gravity. This property is called capillary action and is responsible for its rise in plants from roots to leaves. Plants and trees can’t thrive without capillary action.
Which forces are responsible for dissolving polar substances in water?
Water molecule is polar in nature i.e. hydrogen end of the molecule is partially positive while the oxygen end is partially negative due to the electronegativity difference between both atoms. Polar substances dissolve in water by the ion-dipole force of attraction between ion and water molecules. In this way, the positive end of the substance is attracted by the negative end of the water and vice versa. For example, NaCl is soluble in water.
Why non-polar compounds are insoluble in water?
Non-polar compounds do not have positive and negative ends. They cannot interact favourably with water molecules. Therefore, they do not dissolve in water.
Differentiate between soft and hard water.
| No. | Hard water | Soft water |
| i) | It contains high amount of calcium and magnesium. | It contains high amount of sodium. |
| ii) | It doesn’t form lather with detergents. | It forms lather with detergents. |
| iii) | Forms film on reaction with soap. | Forms suds on reaction with soap. |
| iv) | It leaves deposits called scales. | It leaves no deposits. |
What is difference between biodegradable and non-biodegradable substances?
| Biodegradable substances | Non-biodegradable substances |
| Things that can be easily decomposed by natural agents like water, oxygen, ultraviolet rays of the sun, acid rains, micro-organisms etc., are called biodegradable substances. | Things that cannot be broken down or decomposed into the soil by natural agents are called non-biodegradable substances. |
| Examples: Food waste like vegetable and fruit peels, dead plants and animals, paper materials, etc. | Examples: Plastics, polystyrene, metals, toxic chemicals, paints, tyres, etc. |
