Ans: Water is a chemical compound containing two atoms of hydrogen and one atom of oxygen in a molecule. The molecular formula of water is H2O.
2. Name any three sources of water.
Ans: Any three sources of water are river, ponds and lakes.
3. How many percentage of water is found in sea or ocean.
Ans: 97% of total water is found in sea or ocean.
4. What is ground water?
Ans: Water which is found under the surface of ground is called ground water.
5. Write any two uses of water?
Ans: Water is used for drinking and cooking purpose.
6. What is the boiling point of water?
Ans: The boiling point of water is 100 degree celsius.
7. What is the freezing point of water?
Ans: The freezing point of water is 0 degree celsius.
8. What is hardness?
Ans: Hardness is a tendency of water to make clothing hard with a mineral scum, require extra soap when washing, and leave scale in boilers.
9. Name any two ionic compounds that water cannot dissolve?
Ans: Any two ionic compounds that water cannot dissolve are silver chloride and barium sulphate.
10. How many percentage of total water is used in agriculture?
Ans: About 70% of total water is used for agriculture.
11. Which type of water is bad conductor of electricity?
Ans: Pure water is bad conductor of electricity.
12. What are sources of water?
Ans: The sources of water which are potentially in order to fulfill the necessity of water to the human beings, community and the environment are called sources of water.
13. What are surface water sources?
Ans: Surface water resources are known as the sources of water which are on the surface of the earth.
14. What is hydrology?
Ans: The study of the distribution and movement of water on the earth is called hydrology.
15. Write the physical properties of water.
Ans: The physical properties of water are given below;
• It is tasteless, odourless and colourless.
• Water is only substance on the earth that exist in all three states: solid, liquid and gas.
• Water molecules are attracted by to each other and bonded together by hydrogen bonds. This is called cohesive property of water.
• Water possesses adhesive property.
• Surface tension is the property of water.
• The boiling point of water is 100 degree celsius.
• The freezing point of water zero degree celsius.
• Density of water is greatest at 4°C.
16. What are the chemical properties of water?
Ans: Chemical properties of water are as follows;
Water acts as electrolyte and conducts electricity.
Pure water does not conduct electricity. But in the presence of salts or acid as impurities, it gains the ability to conduct electricity. Water has higher capacity to conduct electricity than other liquids.
In the presence of ionic compound or acid in water, the molecules dissociate into hydronium ions (H3O+) and hydroxyl ion (OH-)due to chemical reactions. This makes the water an electrolyte and it conducts electricity.
H2O + H2O
Amphoteric property of water.
Water acts as an amphoteric compound this is due to the fact that water can self ionize to one hydronium ion and hydroxyl ion.
H2O + H2O
Reactions with alkali metals and alkaline earth metals
Water reacts with alkali metals to form their metallic hydroxides.
2Li + H2O
Lithium hydroxide
2K + H2O
Potassium hydroxide
Mg + 2H2O
Magnesium hydroxide
17. Write the uses of water?
Ans: The uses of water are as follows;
• It is used for drinking purpose.
• About 70% of the total water is used in agriculture for irrigation.
• Water is used to generate hydroelectricity.
• It is used to run industries.
• Water is used for fishery.
• It is largely used by plants for food production and their living.
18. Write any five sources of water?
Ans: Any five sources of water are as follows,
• River
• Groundwater
• Ocean or seas
• Lake
• Rainwater
19. How many types of water are there?
Ans: There are two types of water. They are soft water and hard water.
20. Define hard water with example?
Ans: Hard water is a type of water which cannot form lather with soap. Spring water, water from well, sea water are the examples of hard water.
21. What is soft water?
Ans: Soft water is a type of water which can form lather with soap. Rain water, distilled water are the examples of soft water.
22. What is the reason for permanent hardness of water?
Ans: The permanent hardness of water is due to the presence of chloride and sulphate salt of calcium and magnesium.
23. What is the reason for temporary hardness of water?
Ans: The temporary hardness of water is due to the presence calcium bicarbonate and magnesium bicarbonate.
24. How can be permanent hardness of water can be removed?
Ans: Permanent hardness of water can be removed by treating it with washing soda and by permutit process.
25. How can be temporary hardness of water can be removed?
Ans: Temporary hardness of water can be removed by boiling and treating it with lime water.
26. Write the advantages of hard water.
Ans: The advantages of hard water are as follows;
• it is used in beer industries.
• It controls heart diseases
• The calcium present in hard water makes bones strong.
27. Write the disadvantages of hard water.
Ans: The disadvantages of hard water are as follows;
• It is unfit for drinking purpose.
• It does not form lather with soap easily.
• It decreases the brightness of white clothes, if it is used for washing.
28. Write the difference between hard water and soft water.
Ans:
The differences between hard water and soft water are as follows:
| Hard water | Soft water |
| Contains dissolved salts of Ca, Mg or other heavy metals. | Does not contain dissolved salts. |
| Does not form lather with soap | Forms lather with soap |
| Large quantity of soap is required during washing. | Soap is not wasted |
| Boiling point of hard water is elevated. | Boiling point of soft water is less than of hard water. |
29. Differentiate between carbonate hardness and non-carbonate hardness.
Ans:
The differences between carbonate hardness and non carbonate hardness are as follows:
| Carbonate hardness | Non-carbonate hardness |
| Carbonate hardness is considered temporary | Non-carbonate hardness is considered permanent |
| It can be removed by boiling. | It cannot be removed by boiling. |
| It is due to bicarbonates (HCO3-) of calcium and magnesium. | It is caused by sulphates (SO4--), nitrates (NO3 -), and chlorides (Cl-) of calcium and magnesium. |
30. Which compound is used in permutit process?
Ans: Sodium zeolite or sodium aluminium orthosilicate is used in permutit process.
31. What is zeolite?
Ans: The chemical reagents used in permutit are hydrated sodium aluminium silicate, Na2(Al2Si2O8).XH2O which is called zeolite.
32. Write any three advantages of hard water?
Ans: Any three advantages of hardwater are as follow,
• It is used in beer industries.
• Water becomes tasty to dissolved salts of calcium and magnesium.
• It helps in the development of bones and teeth as it contains calcium salt.
33. Write any one method for the removal of temporary hardness of water.
Ans: The temporary hardness of water can be removed by heating the water and by treating it with lime water.
As we know that, the temporary hardness of water is due to calcium bicarbonate and magnesium bicarbonate. When we heat, calcium bicarbonate and magnesium bicarbonate change into insoluble salts.
Ca(HCO3)2 → CaCO3↓ + H2O + CO2
Mg(HCO3)2 → MgCO3 + H2O + CO2
34. Describe the removal of permanent hardness of water by treating it with washing soda.
Ans: Permanent hardness of water can be removed by treating it with washing soda.
As we know that, the permanent hardness of water is due to soluble salts of calcium and magnesium so when we treat them with washing soda, it changes into insoluble salts.
CaCl2 + Na2CO3 → CaCO3↓ + 2NaCl
CaSO4 + Na2CO3 → CaCO3↓ + Na2SO4
MgCl2 + Na2CO3 → MgCO3↓ + 2NaCl
MgSO4 + Na2CO3 → MgCO3↓ + Na2SO4
35. Define:
a. Conductivity of water
b. Surface tension
c. Aquifer
d. Water table
Ans: b. Surface tension
c. Aquifer
d. Water table
a. Conductivity of water
Conductivity of a water is defined as 'the ability or power of water to conduct or transmit heat, electricity, or sound'.
b. Surface tension
Surface tension is the property of the surface of water that allows it to resist an external force due to the cohesive property of water molecules.
c. Aquifer
Aquifer is an underground bed or layer yielding ground water for wells, springs, etc.
d. Water table
The water collected on the surface over the aquifier inside the earth surface is called water table.
36. What do you mean by amphoteric compound?
Ans: The compounds which can act either as an acid or as a base in a chemical reaction are called amphoteric compounds. Water acts as an amphoteric compound.
37. What is meant by hydrolytic reaction of water? Write any one example.
Ans: Water readily dissolves oxides, carbides, nitrides, etc. of both metals and non metals. The anion of these compounds reacts with hydrogen ion (H+) and their cation reacts with hydroxyl ion (OH-) of water and produce acid and base of both. This reaction is called hydrolytic reaction.
Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH3
38. What is called cohesive property of water?
Ans: Cohesive property is the property of water in which water molecules are attracted to each other and bonded together by hydrogen bonds.
39. What is called adhesive property of water?
Ans: Adhesive property is the property of water in which water molecules stick to other substances and make the substances wet.
40. Write the importance of cohesive and adhesive properties of water in plants.
Ans: Cohesive and adhesive property of water helps to conduct water from the roots to the leaves through the stem.
41. Why is water sticky?
Ans: Water is highly cohesive in nature it is the highest of the non-metallic liquids. Water is sticky and clumps together into drops because of its cohesive properties.
42. Write about the solvent property of water in brief.
Ans:
• Water, which not only dissolves many compounds but also dissolves more substances than any other liquid, is considered the universal solvent.
• A polar molecule with partially-positive and negative charges, it readily dissolves ions and polar molecules. Water is therefore referred to as a solvent: a substance capable of dissolving other polar molecules and ionic compounds.
• The charges associated with these molecules form hydrogen bonds with water, surrounding the particle with water molecules. This is referred to as a sphere of hydration, or a hydration shell, and serves to keep the particles separated or dispersed in the water.
• When ionic compounds are added to water, individual ions interact with the polar regions of the water molecules during the dissociation process, disrupting their ionic bonds.
• Dissociation occurs when atoms or groups of atoms break off from molecules and form ions.
• Since many biomolecules are either polar or charged, water readily dissolves these hydrophilic compounds.
• Water is a poor solvent, however, for hydrophobic molecules such as lipids.
43. What is capillary action?
Ans: The ability of a liquid to rise up in a narrow tube without any external force, against gravity is called capillary action.
44. Define meniscus.
Ans: A meniscus is the curved surface at the top of a column of liquid.
45. What is concave and convex meniscus?
Ans: The shape of the liquid surface in which the sides are raised and the middle is depressed is called concave meniscus. Water forms concave meniscus in a vessel.
The shape of the liquid surface in which the middle part is raised and the sides are depressed is called convex meniscus. Mercury forms convex meniscus.
46. Why does water appear in the form of a curve in the middle of a vessel? Explain.
Ans: Water appears in the form of a curve in the middle of a vessel because of surface tension. Water is made up of polar molecules, which have positively and negatively charged ends. Since opposites attract, the positive sides attract the negative sides, and all of the molecules stick to one another. This is why water droplets can form. Glass molecules also happen to be polar. Again, since polar molecules like to stick together, the water in a glass tube will actually tend to stick to the sides of the tube. We can see this at the top of the graduated cylinder, where the water will slightly creep up the sides and form a curve, which is the meniscus.
47. What is carbonate hardness?
Ans: Alkaline hardness is due to the presence of bicarbonate, carbonate and hydroxides of the hardness-producing metal ions. This is also called carbonate hardness. It is temporary and can be removed easily by boiling.
48. Give various problems caused by hardness.
Ans: Nuisance in bathing, soap doesn’t give lather, nuisance in laundry, a precipitate forms on clothes making them “hard”; and more soap is required in hard water to clean the clothes. Finally, hardness can cause scale in boilers, making them less able to transmit heat.
49. Why is removal of magnesium hardness more expensive than that of calcium?
Ans: It requires more lime because it is a two-step process.
In the first step, the magnesium bicarbonate is added to lime to form magnesium carbonate.
In the second step, additional lime converts the magnesium carbonate into magnesium hydroxide, which precipitates out as a sludge.
50. How do you regenerate zeolite?
Ans: Zeolite can be regenerated by immersing in a strong solution of sodium chloride (NaCl), which is table salt.
51. How do you regenerate ion exchange resin?
Ans: Ion exchange resin can be regenerated by immersing in acid, or a brine solution.