SEE Science : Some Metals

We should study about:
# Introduction to metals
# Some important metals
          *Iron
          *Aluminum
          *Copper
          *Silver
          *Gold
# Position of metals (Fe, Al, Cu, Ag and Au) in periodic table, occurrence and ore, physical properties and uses.
# Occurance of metal in Nepal

Metal: It is more electropositive substance having malleable and ductile property and good conductor of heat and electricity. Metals are extracted from their ores.

Ores:  Ores are the naturally occurring substances from which metals can be extracted conveniently and economically.

Metallurgy: The process of extraction metals from their corresponding ore is called metallurgy.

Iron

Symbol: Fe

Atomatic number: 26

Atomatic weight: 56

Valency: 2 or 3

Ores:

1. Haematite (Fe₂O₃)

2. Magnetite ( Fe₃O₄ )

3. Siderite (FeCo₃  )

4. Iron pyrite

5. Limonite

Physical properties

(i)     Pure iron is a shiny grey-white metal, 

(ii)    lt is malleable and ductile,  

(iii)    It is a good conductor of heat and electricity,  

(iv)    lts specific gravity (i.e. density) is 7.86, 

(v)     It has high melting point (1500°C) and boiling point (2500°C),

Uses of iron

(i)   Iron is used for making rods, pipes and cables.

(ii)      Iron is used to make steel, household utensils, factory equipments, weapons, etc. 

(iii)     Iron is used in bridges, buildings and vehicles. 

(iv)     Iron is used as a catalyst in the preparation of ammonia gas by Haber's process. 

Aluminum

Symbol: Al

Atomatic number: 13

Atomatic weight: 26

Valency: 3

Ores

1.  Bauxite (AI203.2H20)

2.  Felspar [ K(AISiO3O8)]

3.  Diaspore (Al2O3.H2O) 

4.  Clay and Slate ' (AI203.2SiO3.2H2O) 

5.  Cryolite (Na3AIF6) 

6. Kaolin AI2Sl2O7.2H2O

Physical properties

(i)  Aluminium is a bluish-white metal. 

(ii) It is a light metal having density 2.7 gcm³. 

(iii) It is quite malleable and ductile. 

(iv) It is a very good conductor of heat and electricity. 

(v)  Its melting point is 660oC and boiling point is 1800oC. 

(vi)  It can be cast and welded.

Uses

1. Aluminium is used for making household cooking utensils. 

2. Aluminium is used for making overhead electric transmission lines.

3. Aluminium foils are used for packing food items like biscuits, chocolates, medicines, cigarettes, etc.

4. Aluminium metal is used in making bodies and parts of aeroplanes, ships, cars, trucks, trains, photo frames, etc. 

5. It is used for making coins, silver paints and mirrors.

Copper

Symbol: Cu

Atomatic number: 29

Atomatic weight: 63.5

Valency: 1 or 2

Ores

1. Chalcopyrite (CuFeS2)  

2. Chalcocyte (Cu2S)  

3. Cuprite (Cu20)  

4. Azurite [Cu(OH)2] 

5. Malachite [CuCO3.Cu(OH)2]

Physical properties

(i) Copper is a reddish-brown metal which is highly malleable and ductile.   

(ii)  lt is an extremely good conductor of heat and electricity.   

(iii)  It is a quite heavy metal having density 8.95 g/cm³.   

(iv)  lts melting point is 1083°C and boiling point is 2350°C.   

(v)  It readily forms alloys like brass (80% copper and 20% zinc), bronze (90% copper and 10% tin) and German silver (60% copper, 20% zinc and 20% nickel.) 

Uses

(i)  Copper is used for making electric wires for household electric wiring, electric motor, dynamos and other electrical appliances as it is highly ductile and one of the best conductors of electricity.   

 (ii)   Copper is used for making cooking utensils, boilers, kettles, calorimeters, etc. as it is             highly malleable and very good conductor of heat.     

(iii)    Copper is used for electroplating and making printed electronic circuits.                          (iv)  Copper is used  for making coins, alloys, 

(v) Copper salt is used as insecticide, fungicide etc.

Silver

Symbol: Ag

Atomatic number: 47

Atomatic weight: 107.8

Valency: 1

Ores

(i) Argentite or silver glance (Ag2S) 

(ii) Horn silver (AgCI) 

(iii)  Silver copper glance [(AgCu)2.S]

(iv)  Pyrolitc or Ruby silver [3Ag2S.Sb2S3]

Physical properties

(i)  It is a shiny white metal. 

(ii) It is a very good conductor of heat and electricity.

(iii) Its specific gravity is . 

(iv) It's melting point is 960°C and boiling point is 1955°C.    

Gold

Symbol: Au

Atomatic number: 79

Atomatic weight: 197.2

Valency: 1 or 3

Ores

1. Reef gold

2. Sandy alluvial soil

3. Quartz vein

4. Calverite (AuTe2)

Physical properties

(i)  Gold is a lustrous yellow coloured metal.  

(ii)  It is a very good conductor of heat and electricity. 

(iii) It is highly malleable and ductile.  

(iv) It's specific gravityis 19.3 

(v)  It melts at 1063°C and boils at 2530°C.

Uses

(i) It is used for making valuable jewelleries, coins, medals, etc.  

(ii)  It is used in gold plating.  

(iii)     It is used for making statues, gold leaf electroscope crown bridge and medicines.  

(iv)  It is also used in photography. 

1. What happens when silver reacts with hot and concentrated sulphuric acid?
Ans: When silver reacts with hot and concentrated sulphuric acid, silver sulphate, sulphur dioxide and water are formed.

2. What happens when silver reacts with a concentrated nitric acid?
Ans: When silver reacts with concentrated nitric acid, silver nitrate, nitrogen dioxide and water are formed.

3. What happens when gold reacts with the solution of potassium cyanide in the presence of excess air?
Ans: When gold reacts with the solution of potassium cyanide in the presence of excess air, potassium aurocyanide and potassium hydroxide are formed.

4. What is metallurgy?
Ans: Metallurgy is the process of extracting metals from their respective ores.

5. What is crushing of the ore?
Ans: The process in which the lumps of the ores are crushed into smaller pieces with the help of crusher or hammer is called crushing of the ore.

6. What is calcination?
Ans: Calcination is a process of conversion of metallic ores containing carbonates and hydroxides to their respective oxides by heating strongly below their melting point, either in the absence of air or in a limited supply of air.

7. What is roasting?
Ans: Roasting is the process of conversion of the calcinated ore into metallic oxide by heating at a temperature below its melting point in excess of air.

8. What is aquaregia?
Ans: Aquaregia is the mixture of conc. HCl and conc. HNO₃ in the ratio of 3:1.

9. What happens when silver reacts with hot and concentrated sulphuric acid?
Ans: When silver reacts with hot and concentrated sulphuric acid, silver sulphate, sulphur dioxide and water are formed.

10. What happens when silver reacts with a concentrated nitric acid?
Ans: When silver reacts with concentrated nitric acid, silver nitrate, nitrogen dioxide and water are formed.

11. What happens when copper is heated in dry air?
Ans: When copper is heated in dry air, copper is gradually converted into copper oxide and finally red cuprous oxide at a higher temperature.

12. What happens when copper reacts with concentrated hydrochloric acid?
Ans: When copper reacts with a concentrated hydrochloric acid, it forms cuprous chloride with the liberation of hydrogen gas.

13. What is a concentration of the ore?
Ans: The removal of impurities present in the powdered ore is called concentration of the ore.

14. What happens when iron is strongly heated in air?
Ans: When iron is strongly heated in air, it forms a black compound called ferroso-ferric oxide.

15. What happens when iron is exposed to moist air?
Ans: When iron is exposed to moist air, a brown scale of rust is deposited on its surface.

16. What happens when steam is passed over red hot iron?
Ans: When steam is passed over red-hot iron, ferroso-ferric oxide and hydrogen gas are formed.

17. Which gas is produced when iron reacts with a concentrated hot sulphuric acid?
Ans: When iron reacts with a concentrated hot sulphuric acid, sulphur dioxide gas is produced.

18. What are metals?
Ans: Metals are electropositive elements, which are shiny and good conductor of heat and electricity.

19. What are minerals?
Ans: Minerals are the naturally occurring substances having characteristics chemical composition.

20. What are ores?
Ans: Ores are the naturally occurring substances from which metals can be extracted conveniently and economically.

9 Science: Solubility

1. What is a mixture?
Ans: A mixture is a substance formed by mixing two or more than two substances in any proportion by weight in which components of a mixture retain their identity and properties.

2. What do you understand by saturated solution?
Ans: The solution which cannot dissolve any more solute at a particular temperature is called saturated solution.

3. What do you understand by unsaturated solution?
Ans: The solution which can dissolve more solute at a particular temperature is called unsaturated solution.

4. What is a supersaturated solution?
Ans: The solution in which more solute is dissolved by increasing the temperature of a saturated solution is called supersaturated solution.

5. What do you mean by solute?
Ans: The substance which gets dissolved into other substance to form solution is called solute.

6. What is solution?
Ans: Solution is a homogeneous mixture of solute and solvent.

7. What do you mean by solvent?
Ans: The substance which dissolves solute to form solution is called solvent.

8. What is solubility?
Ans: The solubility of a substance at a given temperature is defined as the quantity of the substance that can be dissolved in 100 parts of the solvent at that temperature to give a saturated solution.

9. What is solubility curve?
Ans: A curve obtained by plotting the solubility of a substance at different temperatures is known as solubility curve.

10. What is a crystal?
Ans: Crystal is a homogeneous solid particle which has definite geometrical shape and bounded by plane surfaces meeting at sharp edges.

11. How is supersaturated solution prepared?
Ans: Supersaturated solution is prepared by dissolving more solute in saturated solution by increasing its temperature.

12. The solubility of sodium nitrate is 88 gm at 20°c. What does it mean?
Ans: It means that at 20^oC, 88 gm of sodium nitrate dissolves in 100 gm of water to form the saturated solution.

13. Why is it necessary to mention the temperature along with solubility?
Ans: It is necessary to mention temperature along with solubility because solubility of a solute changes with the change in temperature.

14. What are crystalline substances?
Ans: The substances which have definite geometrical shape are called crystalline substances.

15. What are amorphous substances?
Ans: The substances which do not have definite geometrical shape are called amorphous substances.

16. What is meant by dilute solution?
Ans: The solution in which comparatively less amount of solute is dissolved in the fixed amount of solvent is called dilute solution.

17. What is meant by concentrated solution?
Ans: The solution in which comparatively more amount of solute is dissolved in the fixed amount of solvent is called concentrated solution.

18. What is homogeneous mixture?
Ans: The mixture in which the particles of the components are mixed uniformly is called homogeneous mixture.

19. What is heterogeneous mixture?
Ans: The mixture in which the particles of the components are not mixed uniformly is called heterogeneous mixture.

20. What is crystallization?
Ans: The process of making crystals is called crystallization.

21. Define suspension.
Ans: A suspension is a heterogeneous mixture in which small particles of the solids are spread throughout a liquid without dissolving in it.

22. Define colloid.
Ans: When the diameter of the dissolved particles in the mixture ranges between the sizes of suspension and solution, such a mixture is known as colloid.

23. What is decantation?
Ans: The process of separation of clear liquid from the sediment is known as decantation.

24. What is filtration?
Ans: Filtration is a process by which insoluble solid particles from a solution are separated by a filter paper.

25. What is centrifuging?
Ans: The method of separation of solid from a solution with the help of a centrifuge is called centrifuging.

26. What is distillation?
Ans: The process of purifying a liquid by successive evaporation and condensation is called distillation.

27. What types of substances are separated by sublimation?
Ans: The substances which changes directly into gaseous state due to heat and converts into solid due to cooling can be separated by using sublimation method.

28. What is evaporation?
Ans: The process of conversion of liquid into vapour on heating is called evaporation.

29. What is a mixture ?
Ans: A mixture is mass formed by mixing two or more substances in any proportion by weight without any change in the individual property of the components.

30. Define homogeneous mixture and heterogeneous mixture with examples.
Ans: 
1. Homogeneous mixture: The mixture in which components of the mixture are mixed uniformly with each other is called homogeneous mixture. For example: salt solution, sugar solution etc.
2. Heterogeneous mixture: The mixture in which components of the mixture are not mixed uniformly with each other is called a heterogeneous mixture. For example: muddy water, milk, smoke etc.

31. Differentiate between homogeneous mixture and heterogeneous mixture.
Ans: 

Homogeneous mixture	Heterogeneous mixture
The components are distributed uniformly.	The components are not distributed uniformly.
Each component of the mixture can not be identified by naked eyes.	The components of the mixture can be identified by naked eyes.
A solution is a homogeneous mixture.	A suspension is a heterogeneous mixture.

32. What do you mean by solution? Give one example.
Ans: Solution is defined as a homogeneous mixture of two or more substances. For example sugar solution, salt solution etc.
 
33. Define the terms 'solute' and 'solvent' with one example.
Ans: The substance which gets dissolved and is present in smaller proportion is called the solute. In sugar solution, sugar is solute.
The substance which dissolves the solute and is present in larger proportion is called the solvent. In salt solution, water is solvent.
 
34. Define: Unsaturated solution
Ans: Unsaturated solution: A solution which can dissolve more solute at a particular temperature is known as unsaturated solution at that temperature.
 
35. Define:  Saturated solution
Ans: Saturated solution: A solution which cannot dissolve any more solute at a particular temperature is known as saturated solution at that temperature.
 
36. Define: Supersaturated solution 
Ans: Supersaturated solution: When more quantity of solute is dissolved by raising the temperature of a saturated solution, it is called a supersaturated solution.

37. Define: Amorphous solids
Ans: Amorphous solids: Those solid substances that do not have any definite geometrical forms or shapes are called amorphous solids.

38. Define: Crystalline solids
Ans: Crystalline solids: Those solid substances that have fixed geometrical shapes along with definite and rigid morphology are called crystalline solids.

39. Define: Dilute solution 
Ans: Dilute solution: A solution in which the amount of solution is small compared to that of the solvent is known as a dilute solution.

40. Define: Concentrated solutio
 Ans: Concentrated solution: A solution in which the amount of the solute is large compared to that of the solvent is known as concentrated solution.

41. Differentiate between Saturated solution and unsaturated solution.
Ans: The differences between saturated solution and unsaturated solution are as follows:

Saturated solution	Unsaturated solution
A solution in which more solute can not dissolve at a particular temperature.	A solution in which more solute can dissolve at a particular temperature.
It may be unsaturated on heating.	It remains unsaturated on heating.
Precipitation of the solute appears on cooling.	Precipitation of the solute does not appears on cooling.
It has more density.	It has less density.
It has more concentration of the solute.	It has less concentration of the solute.

42. Differentiate between amorphous and crystalline solids.
Ans: 

Amorphous solid	Crystalline solid
These substances do not have definite geometrical shape.	These substances have definite geometrical shape.
Glass, rubber plastics are the examples of amorphous solid.	NaCl, CuSO4 are the examples of crystalline solid.

43. Differentiate between dilute and concentrated solution.
Ans: 

Concentrated Solution	Dilute solution
If the amount of solute is comparatively higher in a solution then it is a concentrated solution.	If the amount of solute is comparatively lower in a solution then it is a dilute solution.
It is more reactive.	It is less reactive.

44. “Solution is a homogeneous mixture”. Justify.
Ans: A mixture which can not be seen through our naked eyes is called homogeneous mixture. Since solution is the mixture of two or more substances in which components of solvent is in larger proportion than in solute, it is called homogeneous mixture of solution. Example: Salt and water etc.
 
45. How can you identify unsaturated, saturated and supersaturated solutions ? 
Ans: Take three beakers; put a small crystal of solute.
If the concentration is same and solid do not dissolve the solution is saturated mixture of solution.
If the solid crystal dissolves partially or completely then the solution is unsaturated.
If the solid crystal grows in size and the concentration of solution falls then it is called supersaturated. 

46. List some significances of a solution in our daily life.
Ans: Significances of a solution in our daily life are listed below:
1. Plants take mineral salts in the form of solution from the soil.
2. The food that we take absorbed in the form of solution.
3. Aquatic animals take oxygen dissolved in water.
4. We take medicines in the form of solution.
 
47. When a saturated solution at a high temperature is cooled, why is the solution separated as a solid ?
Ans: When a saturated solution at a high temperature is cooled, inter molecular space between the molecules of the solution decreases. As a result, no more solute can remain in a solution separating out as a solid crystal.

48. If some solute added can be dissolved in a solution at a certain temperature, what is the type of solution ? 
 Ans: It is unsaturated solution.

49. If the crystals of Copper Sulphate are kept in its saturated and super saturated solution separated, what will happen to the crystals ?
Ans: The size of CuSO₄ crystal remains same on saturated solution and the size of the CuSO₄crystal increases in supersaturated solution.

50. If the concentration of a solution reduces and crystal appears when solute is added to the solution at temperature 40°C, name the type of solution.
Ans: It is saturated solution.

51. What is meant by the solubility of a substance? Write down the formula which is used to calculate the solubility.
Ans: The solubility of a substance at a particular is defined as the amount of solute dissolved in 100gm of solvent to a saturated solution at that temperature. Mathematically,
Solubility = Weight of solute(gm)Weight of solvent(gm)×100

52. The solubility of sugar at 30°C is 220. What does it mean ?
Ans: This means 220g of sugar is dissolved in 100g of solvent to make saturated solution at 30° C
 
53. Differentiate between colloids and suspension.
Ans: The components of colloidal can be separated by sedimentation or filtration.

Colloid	Suspension
The diameter of the particle of a substance in a solvent is 10-3cm to 10-7cm  and particles are not visible to naked eyes.	The diameter of the particle is greater than 10-3cm in diameter and particles are visible to naked eyes.
The components of colloidal cannot be separated by sedimentation or filtration.	The components of colloidal can be separated by sedimentation or filtration.

54. What is a solubility curve ? What can be known from the solubility curve ? 
Ans: A curve obtained by plotting the solubility of a substance at different temperature is known as solubility curve. Solubility of a substance at different temperature can be known from the solubility curve.

55. List any four applications of a solubility curve.
Ans: Applications of a solubility curve are listed below:
1. The solubility of a substance at a particular temperature can be found.
2. The solubilities of two or more substances at the same temperature can be compared.
3. The solubility curve shows how the solubility of substance varies with the rise in temperature.
4. With the help of solubility curve, the amount of solute that precipitates out when a saturated solution at higher temperature is cooled to a lower temperature can be calculated.

56. What is crystal ? How are crystals prepared ?
Ans: Crystals are homogeneous solids bounded by plane surfaces, meeting in sharp edges and having regular and definite geometrical shape. When a saturated solution of a solid in a liquid at higher temperature is allowed to cool then crystals are formed.

57. What is crystallization ?
Ans: When a saturated solution of a solid in a liquid at higher temperature is allowed to cool, a quantity of solid is deposited in the form of crystals. This process is known as crystallization.

58. Explain the process of formation of copper sulphate crystals.
Ans: Take a solution of copper sulphate in basin and make it saturated by dissolving more copper sulphate or by heating the solvent .Supply the heat until small crystals appears and then remove the heat and cool it in air. Separate the crystal from the mother liquor and put it on a filter paper to dry. Hence in this way crystal of CuSO₄is prepared.
 
59. Temperature is mentioned along with the solubility of a substance. Why ?
Ans: Temperature is mentioned along with the solubility of a substance because solubility changes on changing the temperature.

60. The solubility of CaSO₄ at 20°C is 21. What does it mean ? 
Ans: It means 21 gm CuSO₄ can dissolve in 100gm of water to make saturated solution of CuSO₄ at 20°C.

61. List the types of mixture on the basis of size of particle.
Ans: Mixtures are of three types on the basis of size of particles, they are:
1. Solution (<10^-7cm)
2. Colloids (10^-7cm to 10^-3cm)
3. Suspension (>10^-3cm)

62. Define: Solution 
 Ans: Solution: Homogeneous mixture of two or more substance is called solution. In solution, the particles are of 10^-7cm or smaller in size. Example: sugar solution, salt solution
 
63. Define: Colloids 
Ans: Colloids: If the particles in a homogeneous mixture are 10^-7 to 10^-5 cm in size, such mixture is known as colloids. This state falls in between solution and colloids.

64. Define: Suspension
Ans: Suspension: If the size of the particles is 10^-5 cm or bigger in a heterogeneous mixture, it is known as suspension.

65. Why does a solute dissolve quickly at high temperature and at powdered state ? 
Ans: When solid is heated, its molecule gain more energy and start to vibrate vigorously. On heating solvent, the molecules of liquid gain more energy and start moving vigorously, so that, intermolecular space increases. When the intermolecular space increases, then the dissolving capacity also increases. Thus, the solubility of a substance increases on heating.
If the solute particular are converted into powder, then the surface area of solute increases. It makes the molecule of solvent come in contact with molecules of solute at faster rate and it dissolves quickly.

66. Define the terms 'solute' and 'solvent' with one example each.
Ans: Solute is defined as the substance which gets dissolved and is present in smaller proportion is called the solute. Example: In sugar solution, sugar is solute.
Solvent is defined as the substance which dissolves the solute and is present in larger proportion is called solvent.
Example: In salt solution, water is a solvent.

67. What is the saturated solution ?
 Ans: The solution in which more amount of solute can dissolve in given solvent at given temperature.

68. What is meant by the solubility of a substance ? Write down the formula which is used to calculate the solubility.
Ans: The solubility of a substance at a particular is defined as the amount of solute dissolved in 100gm of solvent to a saturated solution at that temperature.
Mathematically,
   Solubility =  Weight of solute(W₁)Weight of solvent(W₂) × 100
 
69. List any three applications of a solubility curve.
Ans: Applications of a solubility curve are listed below:
1. The solubility of a substance at a particular temperature can be found.
2. The solubility's of two or more substances of the same temperature can be compared.
3. The solubility curve shows how the solubility of substance varies with the rise in temperature.
4. With the help of solubility curve, the amount of solute that precipitates out when a saturated solution at higher temperature is cooled to a lower temperature can be calculated.

70. What is crystal ? How are crystals prepared ?
Ans: Crystals are homogeneous solids bounded by plane surfaces, meeting in sharp edges and having regular and definite geometrical shape. When a saturated solution of a solid in a liquid at higher temperature is allowed to cool then crystals are formed.

71. What is crystallization ? 
 Ans: When a saturated solution of a solid in a liquid at higher temperature is allowed to cool, a quantity of solid is deposited in the form of crystals. This process is known as crystallization.
 
72. Temperature is mentioned along with the solubility of a substance. Why ?
Ans: Temperature is mentioned along with the solubility of a substance because solubility changes on changing the temperature.

73. The solubility of CaSO₄ at 20°C is 21. What does it mean ?
 Ans: It means 21 gm CuSO₄ can dissolve in 100gm of water to make saturated solution of CuSO₄ at 20°C.
 
74. Give Reasons:      In winter, soap does not properly dissolve in water.
Ans: It is because in winter, due to low temperature of water, it cannot dissolve enough soap in it to form proper lather.
 
75. Give Reasons: A saturated solution becomes unsaturated on heating.
Ans: When a saturated solution is heated, the intermolecular space increases and more particles of solute can be adjusted there.

76. Give Reasons:

Water is the universal solvent.

Ans: Water can dissolve many types of solute in it so, it is called universal solvent.

77. Give Reasons:    Brass is a solution.
Ans:  Brass is an alloy formed by mixing two metals: copper and zinc in a proper ratio. It is special type of solution of two solutes and the particles of any solute of the component is not visible in it.

78. Give Reasons:
         Temperature is mentioned with solubility.
Ans: Since the solubility of substance is different at different temperatures, the temperature is mentioned with solubility.

79.  When 15gm of a saturated solution of sodium nitrate at 30°C is cooled down at 10°C, then how much sodium nitrate will be precipitated if solubility of sodium nitrate at 30°C is 95 and 10°C is 30 respectively ?
Solution:
According to the statement :
At 30°C , 95g of NaNO₃ form 195 g of saturated solution 
At 10°C, 30g of NaNO₃, form 130 g of saturated solution 
The difference in the weight of solution is : 195 - 130 = 65g
It shows that,
195 g of saturated solution is cooled from 30°C to 10°C 
it separates 65195 of NaNO₃ 
Therefore, 15 g of saturated solution is when cooled from 30°C to 10°C
It separates 65195 × 15g of NaNO₃ = 5g

Thus, 5g sodium nitrate is separated by cooling the solution.

80. If 70 gram of a saturated solution of sodium nitrate in water at 30°C, contains 15 gram of solute, find the solubility of sodium nitrate at that temperature. 
 Solution: 
Weight of saturated solution(W)  = 70gm
Weight of solute(W₁)  = 15gm

Weight of solvent (W₂) = Weight of saturated solution - Wt. of solute 
                                       = (70 - 15)g
                                       = 55g
Solubility(s) = ?
We know that, 
Solubility(s) = Weight of solute(W₁)Weight of solvent(W₂)  × 100
                      = 1555 × 100
                      = 27.27
Therefore, the solubility of sodium nitrate at 30°C is 27.27.

81. At 20°C, 4.1 gram of sugar dissolves in 2.5 gram of water to form a saturated sugar solution.  Find the solubility of sugar.
Ans: Solution:
 Weight of solute (W₁) = 4.1gm.
Weight of solvent (W₂) = 2.5 gm.
Solubility at 20°C(s) = ?
We know that, 
Solubility (S) = Weight of solute(W₁)Weight of solvent(W₂) ×100
                      = 164
Therefore, the solubility of sugar at 20°C is 164 .
 
 82. At 40°C, 45gm of KCl dissolves in 30gm of water  to form a saturated solution. Find the solubility of KCl. 
Solution:
Weight of solute (W₁) =  45g
Weight of solvent (W₂) = 30g
Solubility at 40° C =?
We have,
Solubility at 40°C  = Weight of solute(W₁)Weight of solvent(W₂)  × 100

                               =  4530 × 100
                               = 150    
Therefore, the solubility of potassium chloride at 40° C is 150.

83. At 30°C, 103 gm of saturated solution of NaCl contains 30.9gm of NaCl. Find the solubility of NaCl at 30°C.
Solution:
Weight of solute (W₁) = 30.9g
Weight of saturated solution (W) = 103g
Weight of solvent (W₂) = Weight of saturated solution (W) – Weight of solute (W₁)                       
                                      = (103 – 30.9)g 
                                      = 72.1 g
We know that,
Solubility at 30° = Weight of solute(W₁)Weight of solvent(W₂) × 100
                = 30.972.1  × 100

                = 42.86
Therefore, the solubility of NaCl at 30°C is 42.86.
 
 84. 5g of water dissolves 60 gm of NH₄NO₃ in it to form a saturated solution at 30°C. Calculate the solubility of NH₄NO₃ at that temperature.
Solution:
Weight of solute (w₁) = 60g
Weight of solvent (w₂) = 5g
We have,
Solubility at 30°  =  Weight of solute(W₁)Weight of solvent(W₂) × 100
                            =  605 × 100
                            = 1200
Therefore, the solubility of NH4NO3 at 30°C is 1200. 

85. How much of CuSO₄ crystals will be separated if 25 g of saturated solution of CuSO₄ at 60°C is cooled down to 30°C if solubility of copper sulphate at 60°C and 30°C are 50 and 30 respectively.
Solution:
At 60° C, 50g of copper solution form 150g of saturated solution.
Similarly at 30° C, 30g of copper solution form 130g of saturated solution.
The difference in the weight of solution = (150 – 130)g
                                                                = 20g
From above,
When 150g of saturated solution is cooled from 60° C to 30° C it separates out 20g of CuSO₄.

When 1g of saturated solution is cooled from 60° C to 30° C it separates out 20/150 g of CuSO₄.

When 25g of saturated solution is cooled from 60° C to 30° C it separates out 20150 × 25 = 3.33g of CuSO₄.
Therefore, 3.33g of CuSO4 is separated on cooling 25g of CuSO₄ from 60°C to 30°C.

86. What is a solubility curve ? What can be known from the solubility curve ?
Ans: A curve obtained by plotting the solubility of a substance at different temperature is known as solubility curve. Solubility of a substance at different temperature can be known from the solubility curve. A diagram of solubility curve is shown in the figure below:
 
 
 .


 

 

 
 
 
 

 

9 Science: Some Gases

1. Why hydrogen is called the simplest element?
Ans: Hydrogen is called the simplest element because it is composed of a proton and an electron.

2. What is hydrogen?
Ans: Hydrogen is the lightest gaseous element situated on first period and group IA of the periodic table.

3. How hydrogen is manufactured in the industry?
Ans: Hydrogen is manufactured in industry by the reaction of hydrocarbon with water vapour.

4. What is a catalyst?
Ans: A catalyst is a chemical substance which increases or decreases the rate of chemical reaction but never participates in the reaction.

5. What happens when magnesium is burnt?
Ans: When magnesium is burnt, magnesium metal reacts with oxygen present in air and magnesium oxide is formed.

6. Why is nitrogen gas filled in electric bulbs?
Ans: Nitrogen gas is filled in electric bulb because it does not react with oxygen and prevents burning.

7. What is nascent hydroge?
Ans: The hydrogen atom at the moment of birth which is highly reactive is called nascent hydrogen.


8. What is hydrogenation?
Ans: Hydrogenation is the process by which vegetable oil is changed into vanaspati ghee.

9. What are the methods applied for extracting hydrogen from water?
Ans: Hydrogen gas is extracted by the electrolysis of water and by the action of certain metals on water.

10. In which electrode is hydrogen gas collected ?
Ans: Hydrogen gas is collected in the cathode during the electrolysis of water.

11. Why is nickel used in the manufacture of hydrogen gas?
Ans: Nickel is used in the manufacture of hydrogen gas because it acts as a positive catalyst which increases the rate of production of hydrogen gas.

12. What happens when hydrogen is passed through a red hot copper oxide?
Ans: When hydrogen gas is passed through a red hot copper oxide, copper oxide is reduced to copper and water is produced.

13. What should be done to extract lead oxide?
Ans: Hydrogen gas should be passed through the heated lead oxide to extract lead.

14. Why do we use manganese dioxide while preparing oxygen gas?
Ans: Manganese dioxide is used while preparing oxygen gas because it is acts as a positive catalyst which helps in early releasing of oxygen from potassium chlorate at lower temperature.

15. State the principle of laboratory preparation of hydrogen gas.
Ans: Hydrogen gas can be prepared in laboratory by the action of dilute hydrochloric acid or sulphuric acid on zinc metal.

16. What is the position of oxygen in the periodic table?
Ans: Oxygen is situated in second period and group VIA of the periodic table.

17. How do aquatic animals get oxygen?
Ans: Aquatic animals absorb the dissolved oxygen in water for breathing.

18. Why is oxygen collected by downward displacement of water?
Ans: Oxygen is collected by downward displacement of water because it is slightly soluble in water and is less dense than water.

19. How do you understand by Haber’s process?
Ans: The process of manufacture of ammonia by the reaction of nitrogen and hydrogen in the ratio 1: 3 at 500°C temperature and 200 atm. pressure in the presence of iron catalyst and molybdenum promoter is known as Haber’s process.

20. Hydrogen is generally not found in air in free state. Why?
Ans: Since hydrogen is more reactive gas; it reacts with other elements very easily, so it is generally not found in free state.

21. Why granulated zinc is used instead of pure zinc during lab preparation of hydrogen gas?
Ans: It is because pure zinc reacts slowly with dilute sulphuric acid but granulated zinc reacts fast.

22. Why nitrogen gas is used for replacing fuels in tanks of aeroplanes?
Ans: It is because nitrogen gas being inactive gas prevents the formation of explosive mixture of fuel and air.

23. Why nitrogen gas is called an inactive gas?
Ans: Nitrogen gas is called an inactive gas because it is chemically inert gas and does not take part in chemical reaction.

24. Who discovered hydrogen gas ?
Ans: A British scientist, Henry Cavendish discovered Hydrogen gas in 1776.

25. Write any 4 physical properties of hydrogen. 
Ans:  The physical properties of hydrogen are as follows:
•    It is colorless, odourlees and tasteless gas.
•    It is lighter than air. 
•    It is slightly soluble in water. 
•    Its melting point is -259°C and boiling point is -253 °C.
 
26. What is the melting point of hydrogen ?
Ans: The melting point of hydrogen is -259°C.

27. Why is hydrogen gas collected by downward displacement of water ? 
Ans:  Hydrogen gas is collected by the downward displacement of water because it is lighter than the air.

28.  What is water gas ?
Ans: The mixture of carbon monoxide and hydrogen gas is called water gas. It is used in industry as a source of heat.

 29. Why is hydrogen gas not found in air ?
Ans: Hydrogen gas is not found in air because it is lighter than air and is very reactive so it takes part in chemical reaction to give rise to the different compounds.
 
30. Give any four precautions which we should follow during the laboratory preparation of hydrogen gas ?
Ans:  Precautions which we should follow during the laboratory preparation of Hydrogen gas are as follows:
•    Concentrated acid should not be used.
•    Impure zinc should be used so that reaction occurs at fast rate.
•    The apparatus should be made air tight.
•    The end of funnel should be dipped inside the acid in thistle but the delivery tube should not be dipped as gases may escape out.

 31. How do you test hydrogen gas ?
Ans: Hydrogen gas is highly combustible gas but not supporter of combustion. When a burning matchstick is brought near a test tube full of hydrogen gas then the fire goes out producing 'pop' sound and hydrogen gas gets burned with a blue flame. Thus, we can say that hydrogen gas does not help other substances to burn.

32. What is nascent hydrogen ?
Ans:  The atomic form of hydrogen produced at the time of chemical reaction is known as nascent hydrogen. Nascent means newly born.

33. How is hydrogen manufactured from methane ?
Ans: In the industrial sector, hydrogen is produced by the reaction between hydrocarbon and water vapor.
For industrial purpose, hydrogen gas is prepared by reacting methane with water vapour at very high temperature in the presence of nickel powder, which acts as catalyst in a reaction.
CH₄ + H₂O   → CO + 3H₂
 
34. Define hydrogenation. 
Ans: Under suitable conditions of temperature and pressure, unsaturated hydrocarbons directly combine with hydrogen gas to form saturated hydrocarbons. This process is known as hydrogenation.

35. What do you mean by a reduction reaction and a reducing agent ?
Ans: When dry hydrogen is passed over the heated oxides of metal like iron, copper and lead, metal gets separated and water is formed. So the removal of oxygen from their metal oxides is called reduction reaction and the hydrogen which brings the reduction is reducing agent.

36. What happens when:-
a) Hydrogen is passed over hot ferric oxide.
b) Hydrogen combines with chlorine.
c) Iron reacts with hydrochloric acid.
d) Hydrogen burns with oxygen.
Ans:  a. Fe₂O₃  +  3H₂     →       2Fe   3H₂O 
b. H₂   +  Cl₂     →    2HCl
c. Fe  + 2HCl        →     FeCl₂  +  H₂
d. When hydrogen is mixed in air, it burns with a pop sound and forms water. But pure hydrogen gas burns with light flame when mixed with oxygen to form water.           2H₂ + O₂         →       2H₂O

 37. Generally hydrogen is not found in the air in free state. Why ?
Ans:  Hydrogen is more reactive gas. Therefore, it reacts with other elements moreover, it is the lightest gas. Therefore, it is generally not found in atmosphere.
 
38. Impure granulated zinc is used instead of pure zinc during lab preparation of hydrogen gas, why ?
Ans: Pure zinc reacts with dilute sulphuric acid slowly but the granulated zinc reacts with dilute sulphuric acid fast. Therefore, granulated zinc is used instead of pure zinc during lab preparation of hydrogen gas.

39. Many metals displace the hydrogen from the acids, why ?
Ans:  It is because metal are more reactive or more electropositive than hydrogen.

40. Oxides of zinc, calcium and magnesium are not reduced by hydrogen, why ?
Ans: It is because the metals mentioned above are more reactive than hydrogen.

41. Zinc is mostly used for the laboratory preparation of hydrogen gas rather than others metals, why ?
Ans: It is because of the following facts:  
•    Metals like sodium and potassium reacts violently with acid.
•    Calcium and magnesium are very expensive in comparison to zinc.
•    Aluminium forms a protective coating of Al₂0₃  whereas iron reacts with acid very slowly and requires more heat. 
 
42. What is the role of manganese dioxide in the preparation of oxygen gas in the laboratory ?
Ans: Manganese dioxide is used in a preparation of oxygen gas as a positive catalyst which accelerates the rate of chemical reaction.

43. What happens when the potassium permanganate is heated ?
Ans: When the potassium permanganate is heated, it gives rise to the manganese oxide and oxygen gas. The reaction occurs as follows:
                2KMnO₄  → K₂MnO₄ + MnO₂ + O₂

 44. Enlist the physical properties of oxygen gas?
Ans: Physical properties of oxygen gas: 
•    It is a neutral gas doesn’t have any effect on the indicators.
•    It is colorless odorless and tasteless gas.
•    It is heavier than air.
•    It is slightly soluble in water.
 
45. What is the position of oxygen in periodic table ?
Ans: Oxygen is the first member of the group VIA on the periodic table. It is located in period 2 and group 16.
 
46. What are the uses of oxygen ?
Ans: We used oxygen for respiration as fuel and welding and cutting of metals also.
 
47. What are the physical properties of oxygen ?
Ans: The physical properties of oxygen are: 
•    Oxygen is colorless, odourless and tasteless gas.    
•    It is slightly soluble in water.
•    It is neutral to indicator.
 
48. How will you prepare oxygen gas in the laboratory ? 
Ans:  In a laboratory oxygen gas is prepare by heating the potassium chlorate and manganese dioxide acts as a catalyst.

49. What happens when burning charcoal is kept in gas jar containing oxygen ? 
Ans: When burning charcoal is kept in the jar containing oxygen gas carbon dioxide is formed.
        C    +    O₂    →     CO₂

50. What is rusting of iron ?
Ans: The process of forming rust when iron reacts with oxygen in the presence of moisture.
   4Fe    + 3O₂ + xH₂O        →       2Fe₂O₃..xH₂O

51. What do you mean by oxy-acetylene flame ? 
 Ans: The flame made by burning oxygen and acetylene and used for cutting and welding metals is called oxy-acetylene flame.

52. Some amount of oxygen is dissolved in water, why ? 
Ans: It is because the solution of oxygen in water provides the source of oxygen for respiration for the aquatic animals.
 
53. What happens when an alkaline pyrogallol solution is added to an oxygen containing jar ?
Ans: When the alkaline pyrogallol solution is added to an oxygen containing jar, the oxygen gets dissolved in it giving rise to the dark brown color to the solution.
 
54. How can we prepare oxygen gas in laboratory without heat ?
Ans: Oxygen is prepared in the laboratory by the decomposition of hydrogen peroxide (H₂O₂) into water and oxygen in the presence of Manganese dioxide (MnO₂) as catalyst.                                                                                 

55. What are the uses of oxygen ?
Ans: The three uses of oxygen are as follows:  
•    Living organisms use oxygen during respiration.
•    Liquid oxygen is used as fuel in missile and rocket.
•    Mountaineers carry oxygen cylinders and masks with them so that they can breathe easily at high altitude


 56. What happens when the following elements and compounds burn in oxygen ? Write the chemical reaction.
a) Calcium
b) Phosphorus
c) Magnesium
d) Glucose
Ans: a.  Calcium oxide is formed.
          2Ca + O₂       →     2CaO
b. Phosphorous pentoxide is formed
           4P      +      5O₂       →      2P₂O₅
c. When magnesium is burnt in air then magnesium oxide is formed. Magnesium reacts with air and forms magnesium oxide which is an alkali.
          2Mg   +   O₂         →         2MgO
d. Energy is released.
 C₆H₁₂O₆    +    6O₂     →    6CO₂  + 6H₂O + energy

57. What is the position of nitrogen in periodic table ?
Ans: Nitrogen has 5 electrons in its valence shell and it belongs to the VA group of periodic table. As there are two shells, it belongs to the 2nd period of the periodic table. It is non – metal.
 
58. How will you prepare nitrogen gas in industrial scale ?
 Ans: In the industrial sector, ammonia is manufactured at the Haber's synthesis process. In this process, nitrogen and hydrogen are heated in the ratio of 1:3 in the presence of iron as catalyst and molybdenum as promoter at temperature of about 500°C, under high pressure of about 200 - 900 atmospheric pressure. 
     N2        +         3H₂       →       2NH₃

59. What are the physical properties of nitrogen ?
Ans:  Physical properties of nitrogen are as follows: 
•    It is colorless, odorless and tasteless.
•    It is slightly lighter than air.
•    It is not soluble in water.
 
60. What happens when a burning magnesium ribbon is inserted in a jar containing nitrogen gas ? Also write the chemical equation.
Ans: When the magnesium ribbon is inserted in the jar containing the nitrogen gas, it burns and produce the yellowish white color  called magnesium nitride.
        3Mg     +      N₂             →          Mg₃N₂

 61. What is chemical nitrogen ?
Ans: The nitrogen obtained from the nitrogenous compound in its pure form is called chemical nitrogen.
 
62. What happens when nitrogen combines with oxygen at a high temperature ?
Ans: At very high temperature, nitrogen and oxygen combines with to form a nitric oxide.
             N₂     +    O₂             →        2NO

 63. Describe the preparation of nitrogen by heating copper method in short.
Ans: At first, air is passed through lime water and then to conc. Sulphuric acid to make air free from carbon dioxide gas .Now the air contains nitrogen and oxygen which is passed over heated copper. As the nitrogen escapes away, oxygen reacts with copper to produce copper oxide.
              2Cu      +     O₂        →          2CuO
 
64. What is nitrogen ?
Ans:  Nitrogen is an inert gas which constitutes about 78% by the volume of the atmosphere.

65. What are the three uses of nitrogen ? 
Ans: We use nitrogen gas for: 
•    Manufacturing nitric acid.
•    Manufacturing of nitrogen rich fertilizer.
•    Nitrogen gas is used to manufacture explosive.

66. Nitrogen gas is an inactive gas, why ?
Ans: Molecules of nitrogen gas are formed by the combination of two atoms of Nitrogen. These two atoms are held together by a very strong triple bond. Since huge amount of energy is required to break this bond, nitrogen does not take part in chemical reaction. Thus the nitrogen is an inactive gas.
 
67. Nitrogen gas is used for replacing fuels in fuel tank of aeroplanes, why ?
Ans: Nitrogen gas being inactive gas prevents the formation of explosive mixture of fuel and air. Therefore, it is used for replacing fuels in fuels tanks of aeroplanes.

68. What is Haber’s process ? Write with balanced chemical equation.
Ans:  When a mixture of hydrogen and nitrogen in the ratio of 3:1 by volume is heated to about 450°C under the pressure of 200 - 600 atmosphere in the presence of finely divided iron as catalyst and Molybdenum (Mo)  as promoter, ammonia gas is produced. This process is known as Haber’s process.                                                                   

69. What is biocatalyst ?
Ans:  Biocatalyst is the biochemical compound like enzyme that helps to increase or decrease the rate of chemical reaction.
 
70. What are isotopes ? 
Ans: Isotopes are the elements having the same atomic number but different atomic masses.

71. What is combustion ? 
Ans: Combustion is the process of burning hydrogen with oxygen to produce water.
 
72. Answer the following question after observing the figure .

a) Which gas is going to be prepared in the figure?
b) What are the mistakes in the arrangement? Correct the figure.
c) Write the formula equation for the preparation of the gas? 
d) What happens when a burning match stick is held near the gas jar? 
e) Give any three uses of the gas? 
f) What happens when concentrated sulphuric acid is used instead of dilute sulphuric acid in it? 

Ans: a. Hydrogen gas
b. The end of thistle funnel must be under the acid in Woulfe’s bottle and delivery tube should not be dipped under the acid in Woulfe’s bottle.
c. Granulated Zn  +  H₂SO₄   →  ZnSO₄     +     H₂
d. When a burning matchstick is brought near a test tube full of hydrogen gas then the fire goes out producing pop sound forming blue flume. 
e. The main uses of hydrogen are as follows:
    • It is used as a reducing agent in industries and laboratory.
    • It is used to fill in the balloons as it is the lightest gas but it is mixed with helium as hydrogen is highly inflammable.
    • It is used to prepare chemical fertilizers.
f. If conc. sulphuric acid is used instead of dilute sulphuric acid, suphur dioxide is produced instead of hydrogen gas.
 Zn  +  conc.H₂SO₄         →  ZnO  +  H₂O  +   SO₂ 
Instead when the dilute H₂SO₄ is used, the following reaction occurs to form the hydrogen gas.
 Zn  +  dil. H₂SO₄  →  ZnSO₄  + H₂

73. How is hydrogen manufactured from electrolysis of water ?
Ans: The process of the decomposition of the water into oxygen and hydrogen gas when the electric current is passed through the water is called Electrolysis of water.
         
                Fig: Electrolysis of water
When dil. H₂SO₄ is mixed with water
H₂O(HOH)      →     H⁺  +     OH^-
At anode
OH^{- -}    →     OH         +       e^-
4OH     →   2H₂O       +       O₂
At cathode
H⁺          +       e^-      →      H
4H      →       2H₂                    
Overall reaction is
2H₂O       →       2H₂    +    O₂
Hence, hydrogen is formed at cathode and oxygen is formed at anode.

 74. How is oxygen gas is prepared in laboratory by the actions of heat ? Draw a necessary labeled diagram and mention the chemical equation.
 Ans: Laboratory preparation of oxygen gas:
For the manufacture of oxygen gas in the laboratory (by heating), potassium chlorate or potassium permanganate is heated in a herd test tube vigorously.
Small amount of potassium permanganate or potassium chlorate is taken in a hard test tube and heated vigorously. A burning matchstick is taken to the test tube and observed. We can see that at very high temperature of (360 – 370)^oC oxygen is evolved. This is high temperature to maintain so manganese dioxide is taken on a different test tube along with potassium chlorate and is heated. Manganese dioxide acts as catalyst and this helps in formation of oxygen at (240-250)^oC. The oxygen produced is collected in the gas jar by downward displacement of water.
    KClO₃                  →              2KCl        +       3O₂


            Fig. Arrangement of apparatus for the preparation of oxygen

75. Which chemical is used for reacting with NH₄Cl to produce nitrogen gas in the laboratory ? Draw a neat and labeled diagram for the preparation of nitrogen gas in the laboratory. Mention the chemical equation.
Ans: Nitrogen gas is prepared in the laboratory by the mixture of sodium nitrate and ammonium chloride is heated. This results in the production of nitrogen which is collected in the gas jar by the downward displacement of water.
 NaNO₂   +     NH₄Cl   →  NaCl  + 2H₂O  +   N₂


 
 76. Write the composition of air.
Ans: Air is composed of mainly nitrogen (78.06%)  and oxygen (21.97%), which occupy about 99% by volume of air. Other minor constituents include  water vapor, dust particles along with other inert gases like neon, argon etc.