Important Questions
1. How do you test that air and water are necessary for metallic corrosion?
(or)
Suggest an experiment to prove that the presence of air and water are essential for corrosion. Explain the procedure.
(or)
What are the reasons for corrosion of metals. How do you verify? (AS 3) 4 Marks
A:
‣ Take three test tubes and place clean iron nails in each of them.
‣ Label these test tubes A, B and C. Pour some water in test tube A and cork it.
‣ Pour boiled distilled water in test tube B, add about 1 ml of oil and cork it.
The oil will float on water and prevent the air from dissolving in the water.
‣ Put some anhydrous Calcium chloride in test tube 'C' and cork it. Anhydrous Calcium chloride will absorb the moisture, if any, from the air.
‣ Leave these test tubes for a few days and then observe them.
‣ You will observe that iron nails in test tube 'A' get rusted. But they do not rusted in test tubes 'B' and 'C'.
‣ In the test tube 'A', the nails are exposed to both air and water. In the test tube 'B' the nails are exposed to only water and the nails in test tube 'C' are exposed to dry air.
‣ From this activity we conclude that both air and water are necessary for corrosion (rusting) of iron.
2. Draw the diagram showing
(i) Froth floatation. (ii) Magnetic Separation. (AS 5) 4 Marks
A: (i) Froth floatation
(ii) Magnetic Separation
3. What are the different stages of extraction of metal from an ore? Write a note on any one of the stages. (AS 1) 4 Marks
A: The extraction of a metal from its ore involves mainly three stages.
They are
(i) Concentration or Dressing
(ii) Extraction of crude metal
(iii) Refining or Purification of the metal
Purification of the crude metal:
Refining of the metal involves several types of processes.
Methods used for refining of metals are
(a) Distillation
(b) Poling
(c) Liquation
(d) Electrolysis
The process that has to be adopted for purification of a given metal depends on the nature of the metal and its impurities.
(a) Distillation: This method is very useful for purification of low boiling metals like Zinc and Mercury containing high boiling metals as impurities. The extracted metal in the molten state is distilled to obtain the pure metal as distillate.
(b) Poling: The molten metal is stirred with logs (poles) of green wood. The impurities are removed either as gases or they get oxidized and form scum (slag) over the surface of the molten metal. Blister copper is purified by this method. The reducing gases, evolved from the wood, prevent the oxidation of Copper.
(c) Liquation: In this method a low melting metal like tin can be made to flow on a slopy surface to separate it from high melting impurities.
(d) Electrolytic refining: In this method, the impure metal is made to act as anode. A strip of the same metal in pure form is used as cathode. They are put in a suitable electrolytic bath containing soluble salt of the same metal. The required metal gets deposited on the cathode in the pure form. The metal, constituting the impurity, goes as the anode mud. The reactions are
Anode: M 
Mn+ + n e-
Cathode: Mn+ + n e- 
M
(M = pure metal)
Where n = 1, 2, 3, ----
4. What are the methods of concentration of ores and explain. (AS 1) 4 Marks
A: The physical methods adopted in dressing of the ore (or) enriching of the ore depends upon difference between physical properties of ore and gangue.
1) Hand Picking: If the ore particles and the impurities are different in one of the properties like colour, size etc., using that property the ore particles are hand picked separating them from other impurities.
2) Washing: Ore particles are crushed and kept on a slopy surface. They are washed with controlled flow of water. Less densive impurities are carried away by water flow, leaving the more densive ore particles behind.
3) Froth flotation: This method is mainly useful for Sulphide ores which have no wetting property where as the impurities get wetted. The ore with impurities is finely powdered and kept in water taken in a floatation cell. Air under pressure is blown to produce forth in water. Forth so produced, takes the ore particles to the surface where as impurities settled at the bottom. Forth is separated and washed to get ore particles
4) Magnetic Separation: If the ore or impurity, one of them is magnetic substance and the other non-magnetic substance they are separated using electromagnets.
5. Explain about the process of extraction of crude metal from the ore? (AS 1) 4 Marks
A: Extraction of crude metal from the ore:
After concentration and dressing of ore that obtained from earth, we get a enriched ore. This enriched ore is to be converted into metallic oxide by reduction reaction. Then this metallic oxide is further reduced to get a metal with certain impurities.
The reduction method depends on the position of the metal in activity series.
1) Metals of high reactivity: The metallic halides or metallic oxides of highly reactive metals are subjected to electrolysis to get the metal.
e.g.: Extraction of Na from NaCl
Fused NaCl is electrolysed with steel cathode (-) and graphite anode (+). The metal (Na) will be deposited at cathode and chloride is liberated at anode.
At cathode : 2 Na+ + 2 e- → 2 Na
At anode : 2 Cl- → Cl2 + 2 e-
2) Moderately reactive metals: The ores of these metals are generally present as Sulphides or Carbonates in native. Therefore prior to reduction of ores of these metals, they must be converted into metal oxides.
Sulphide ores are converted into metal oxides by roasting and carbonate ores by calcination.
These oxides are reduced to metals by various reduction methods. viz... Chemical reduction, auto reduction, displacement method, electrolytic reduction.
3) Low reactive metals: As they are less reactive their ores are often found in free state. The oxides of these metals can be reduced to metals by heat alone and sometimes by displacement from their aqueous solutions.
6. Explain metallic corrosion. Mention the measures methods to be taken to prevent metallic corrosion. (AS 1) (AS 6) 4 Marks
A: * Corrosion is defined as the gradual transformation of a metal into its combined state because of the reaction with the environment. Corrosion is a surface phenomenon.
* The rusting of iron, tarnishing of Silver, development of green coating on Copper and Bronze are examples of corrosion.
* In metallic corrosion, a metal is oxidised by loss of electrons to Oxygen and results in the formation of oxide.
* Corrosion of iron occurs in presence of water and air.
* When iron is exposed to moist air, it is found convered with a reddish brown coating is called rust. (Fe2O3 X H2O)
* During corrosion at a particular spot on the surface of an object made of iron, oxidation takes place and that spot behaves as anode.
At anode: 2 Fe (S) → 2 Fe2+ + 4 e-
* Electrons released at the anodic spot move through the metal and go to another spot on the metal and reduce Oxygen at that spot in presence of H+.
This spot behaves as cathode.
* At Cathode: O2 (g) + 4H+ (aq) + 4e- → 2 H2O (l)
* The overall reaction in rusting of iron is
2 Fe (s) + O2 (g) + 4 H+ (aq) → 2 Fe2+ (aq) + 2 H2O (l)
The Ferrous ions (Fe2+) are further oxidised by atmospheric Oxygen to Ferric ions (Fe3+) which come out as rust in the form of hydrated Ferric oxide (Fe2O3. X H2O)
Prevention of corrosion:
* One of the simplest methods of preventing corrosion is to prevent the surface of the metallic object to come in contact with atmosphere (or) moisture.
* Prevention of corrosion can be done by covering the surface with paint or by some chemicals (bisphenol).
* Corrosion can be protected by coating the metal with more electropositive metal. This can be done by electroplating.
* An electrochemical method is to provide a sacrificial electrode of another metal (Mg, Zn) which corrodes itself but saves the object.
7. Draw the neat diagram of blast furnace and label its parts. (AS 5) 4 Marks
1. Ore + coke + lime stone
2. Iron oxide reduced by CO
3. Waste gases (CO, CO2, N2)
4. Lime reacts with Silica to form slag
5. Steel Shell
6. Iron melts and dissolves C, Si, P
7. Fire bricks
8. Carbon burns to give CO2
9. Hot air blast main
10. Slag out
11. Molten iron out
8. The results of reactions of metals A, B, C, D, E with different solutions are given in the table below.
Observe the table and write answers. (AS 4) 4 Marks
|
Metal |
|
|
Solution |
|
|
|
|
FeSO4 |
CuSO4 |
ZnSO4 |
AgNO3 |
Al(SO4)3 |
|
A |
No |
No |
No |
A layer is |
No |
|
|
reaction |
reaction |
reaction |
formed |
reaction |
|
B |
an ash |
a light |
No |
A layer is |
No |
|
|
coloured |
is brown |
reaction |
formed |
reaction |
|
|
substance |
layer is |
|
|
|
|
|
settled on |
formed on |
|
|
|
|
|
the metal |
the metal |
|
|
|
|
C |
No |
No |
No |
No |
No |
|
|
reaction |
reaction |
reaction |
reaction |
reaction |
|
D |
No |
- |
No |
A layer is |
No |
|
|
reaction |
|
reaction |
formed on the metal |
reaction |
|
E |
- |
a light |
Fresh |
Fresh |
No |
|
|
|
brown |
layer is |
layer is |
reaction |
|
|
|
layer is |
formed |
formed |
|
|
|
|
formed |
a) Which is the highly reactive metal? Why?
b) Which is the least reactive metal? Why?
c) Which metals form brown layer?
d) Arrange the metals A, B, C, D, E in the order of their reactivity?
A: a) Metal 'E' is more reactive among all the metals given because it displaces all the elements from the compounds given in the table.
b) Metal 'C' is the least reactive metal because it does not displace any other metal from the compounds given in the table.
c) Metals B and E will form brown layer.
d) The ascending order is as follows C < A < D < B < E.
9. Draw a flow chart showing various stages involved in extraction of metal from an ore. (AS 4) 4 Marks
A:
10. Complete the following table and answer the questions given below? (AS4) 4 Marks
|
Ore |
Bauxite |
Copper |
Zinc |
Epsom |
Horn |
|
|
|
|
Iron Pyrites |
Blende |
Salt |
silver |
|
|
Formula |
Al2O3. |
CuFeS2 |
|
MgSO4. |
AgCl |
KCl.MgCl2. |
|
Metal |
Al |
|
Zn |
Mg |
|
Mg |
(i) How many water molecules are there in Epsom salt?
(ii) Which metals ore is Bauxite?
(iii) Among the above metals which are available in free state?
(iv) What is the ore of Iron metal?
A:
|
Ore |
Bauxite |
Copper |
Zinc |
Epsom |
Horn |
Carnallite |
|
|
|
Iron Pyrites |
Blende |
Salt |
silver |
|
|
Formula |
Al2O3. |
CuFeS2 |
ZnS |
MgSO4. |
AgCl |
KCl.MgCl2. |
|
Metal |
Al |
Cu |
Zn |
Mg |
Ag |
Mg |
i) 7 Water molecules
ii) Al
iii) Ag
iv) Haematite, Magnetite
11. Which reaction is useful to join broken railings of railway tracks and cracked machine parts? Explain that reactions.
(OR)
What is thermite process? Write the daily life applications on that process. (AS1) (AS6) 4 Marks
A: ¤ The reduction of metal oxides with Aluminium powder is called thermite reaction.
e.g.: Cr2O3 + 2Al → Al2O3 + 2 Cr + heat
* The mixture of concentrated oxide ore and Aluminium powder is called thermite.
* The reducing agent in thermite process is Aluminium.
* The reaction of iron (III) oxide (Fe2O3), with Aluminium produces molten iron which is used to join railings of railway tracks or cracked machine parts
2Al + Fe2O3 → Al2O3 + 2Fe + Heat
12. Explain one method of concentration of a ore in Sulphide form.
(OR)
Explain the process of Froth flotation (AS1) 4 Marks
A: Froth Flotation Process:
* This method is mainly useful for Sulphide ores which have no wetting property where as the impurities get wetted.
* The ore with impurities is finely powdered and kept in water, containing pine oil taken in a flotation cell.
* Air under pressure is blown to produce froth in water.
* Froth so produced, takes the ore particles to the surface, where as impurities settle at the bottom.
* Froth is separated and washed to get ore particles.
13. Explain the following terms.
(1) Roasting (2) Calcination (3) Smelting (AS 1) 4 Marks
A: Roasting: The process in which the ore is heat at high temperature in excess of air or Oxygen below its melting point is called roasting.
(i) Roasting is a pyrochemical process in which the ore is heated in the presence of Oxygen or air below its melting point.
(ii) The products obtained in the process are also produced in solid state
e.g.: 2 Zns + 3 O2 → 2 ZnO + 2 SO2
Calcination: The process in which the ore is heated at high temperature in the absence of air is called calcination.
(i) Calcination is a pyrochemical process in which the ore is heated in the absence of air.
(ii) The ore gets generally decomposed in the process leaving volatile impurity
(CO2)
e.g.: MgCO3 → MgO + CO2 ↑
Smelting: The process in which the mixture of ore, flux and a reducing agent is heated at high temperature above its melting point is called smelting.
i) Smelting is pyrochemical process in which the ore is mixed with flux and fuel and strongly heated.
ii) The heat is so strong that the ore is reduced to even metal and the metal is obtained in molten state.
iii) During smelting, the impurities (gangue) in the ore react with flux to form slag which is removed.
iv) The smelting is carried out in a specially built furnace known as blast furnace.
14. Explain the process of refining Copper by electrolytic method (AS1) 4 Marks
Experimental setup for the electrolytic refining of Copper
* An impure Copper is taken as anode, pure Copper strips are taken as cathode.
* The electrolyte is an acidified solution of Copper sulphate.
* As a result of electrolysis Copper in pure form is transferred from the anode to the cathode.
Reaction at anode: Cu → Cu2+ + 2e-
Reaction at cathode: Cu2+ + 2e- → Cu
* The suitable impurities go in to the solution where as insoluble impurities from the blister Copper deposited at the bottom of the anode.
15. Fill up the following table using the given metals Mg, Al, Cu, Ag, Au, Ca, Na, K, Pb, Zn, Fe. (AS 4) 2 Marks
|
Metals of high |
Metals of medium |
Metals of low |
|
reactivity |
reactivity |
reactivity |
|
|
|
|
A:
|
Metals of high |
Metals of medium |
Metals of low |
|
reactivity |
reactivity |
reactivity |
|
K, Na, Ca, Mg, Al |
Zn, Fe, Pb, Cu |
Ag, Au |
16. Complete the table given below: (AS 4) 2 Marks
|
Ore |
|
Carnallite |
Epsom salt |
Gypsum |
|
Zincite |
|
Formula |
MgCO3 |
|
MgSO4. |
|
CaCO3 |
|
|
|
|
|
7 H2O |
|
|
|
|
Metal |
Mg |
Mg |
|
Ca |
Ca |
Zn |
A:
|
Ore |
Magnesite |
Carnallite |
Epsom salt |
Gypsum |
Limestone |
Zincite |
|
Formula |
MgCO3 |
KCl.MgCl2. |
MgSO4. |
CaSO4. |
CaCO3 |
ZnO |
|
|
|
6 H2O |
7 H2O |
2 H2O |
|
|
|
Metal |
Mg |
Mg |
Mg |
Ca |
Ca |
Zn |
17. Give an example of auto reduction of Sulphide ores.
(OR)
Write about self reduction of Sulphide ores. (AS 1) 2 Marks
A: In The extraction of Copper (Cu), from its Sulphide ore, the ore is subjected to partial roasting in air to give its oxide.
2 Cu2S + 3 O2 → 2 Cu2O + 2 SO2
When the supply of air is stopped and the temperature is raised, the rest of the Sulphide reacts with Cuprous oxide and forms the metal and SO2. So this process is called self auto reduction.
2 Cu2O + Cu2 S → 6 Cu + SO2 ↑
18. When do we use magnetic separation method for concentration of an ore? Explain with an example. (AS 1) 2 Marks
A: Magnetic Separation Method:
If the ore or impurity, one of them is magnetic and the other is non- magnetic they are separated by magnetic Separation method.
e.g.: The magnetic ores like iron pyrites (FeS) and magnetite (Fe3O4) are concentrated by this method. The crushed ore is allowed to pass through electromagnetic belts. The mineral particles are retained and gangue particles are thrown away.
19. Arrange Au, Ca, Mg, Zn in activity Series. (AS1) 1 Mark
A: Ca > Mg > Zn > Au
20. The impurities like clay are called as (AS1) 1 Mark
A: Gangue
21. Give chemical formula of rust. (AS 1) 1 Mark
A: Fe2O3.XH2O
22. What is the role of furnace in metallurgy? (AS1) 1 Mark
A: Furnace is used to carry out pyrochemical process in metallurgy.
23. Name one situation where thermite reaction has seen? (AS6) 1 Mark
A: Railway tracks.
24. Give the name of elements which is in free state. (AS1) 1 Mark
A: Gold, Silver, Platinum
25. Which metals are used in preparation of Ornaments? (AS 6) 1 Mark
A: Gold, Silver, Platinum
26. Which metals are used in preparation of Electric conducting wire. (AS 6) 1 Mark
A: Copper, Aluminium
1. Write the formula of carnallite. (AS1) 1 Mark
A: KCl. MgCl2. 6 H2O
2. Cinnabar ore belongs to which metal extraction? (AS1) 1 Mark
A: Hg - metal ore.
3. Among Zinc blende, Magnasite and Zincite, which ore is carbonate ore? (AS1) 1 Mark
A: Magnasite - MgCO3
4. Among the following (AS1) 1 Mark
K, Zn, Au, Cu
(i) Which is more reactive
(ii) Which is least reactive.
A: (i) K
(ii) Au
5. Write descending order of their reactivity among the following elements.
Zn, Pt, Al, Na, K (AS1) 1 Mark
A: K > Na > Al > Zn > Pt.
6. By which method sulphide is concentrated (AS1) 1 Mark
A: Froth flotation process.
7. Which metals can react with cold water gives H2 gas? (AS1) 1 Mark
A: K, Na, Ca, Mg
8. Which metals react with oxygen gives peroxides? (AS1) 1 Mark
A: K and Na metals gives respective peroxides.
9. Which of the method is used to reduce NaCl to get Na metal. (AS1) 1 Mark
A: Electrolysis method.
10. The extraction of Cu from Cu2S, which substance is used for Auto - reduction of sulphide ore. (AS1) 1 Mark
A: Cu2O
11. Which metal can displace Ag metal from dicyanoargentate solution? (AS1) 1 Mark
A: Zn metal.
12. In purification of metals, at which juncture distillation method is used? (AS1) 1 Mark
A: This method is used in the purification of low boiling metals like Zinc and Mercury containing high boiling metals as impurities.
13. Which purification method is used for Blister copper. (AS1) 1 Mark
A: Poling
14. Which substance is formed during tarnishing of silver? (AS1) 1 Mark
A: Silver Sulphide.
15. Write the formula of Bauxite. (AS1) 1 Mark
A: Al2O3. 2 H2O
16. Write the formula of Haematite. (AS1) 1 Mark
A: Fe2O3
17. Write the formula of Magnetite. (AS1) 1 Mark
A: Fe3O4
18. Name the few highly reactive metals. (AS1) 1 Mark
A: K, Na, Ca, Mg, Al
19. How do you extract highly reactive metals? (AS1) 1 Mark
A: Highly reactive metals can be extracted by electrolysis of their fused compounds
20. Mention the stages involved in extraction of a metal from its ore. (AS1) 2 Marks
A: The extraction of a metal from its ore involves mainly three stages. They are
(i) concentration or dressing
(ii) Extraction of crude metal
(iii) Refining or purification of the metal.
21. Mention some important methods of refining (AS1) 2 Marks
A: The important methods of refining are
(i) Distillation
(ii) Poling
(iii) Liquation
(iv) Electrolysis
22. Arrange the following metals in order of their decreasing reactivity
Ag, K, Cu, Zn, Ca, Hg (AS1) 2 Marks
A: K > Ca > Zn > Cu > Hg > Ag
23. Identify the metal present in the following ores. (AS1) 2 Marks
(i) Zinc Blende
(ii) Pyrolusite
(iii) Galena
(iv) cinnabar
A: (i) Zn (ii) Mn (iii) Pb (iv) Hg
24. Write the balanced chemical equations, extraction of iron from haemetite in the blast furnace. (AS1) 2 Marks
A: 2 C + O2 → 2 CO
Fe2 O3 + 3 CO → 2 Fe + 3 CO2
CaCO3 → CaO + CO2
CaO + SiO2 → CaSiO3
25. explain the auto (self) reduction of sulphide ores (AS1) 2 Marks
A: (i) In the extraction of Cu from its sulphide ore, the ore is subjected to partial
roasting in air to give its oxide.
2 Cu2S + 3 O2 → 2 Cu2O + 2 SO2
(ii) When the supply of air is stopped and temperature is raised. The rest of the sulphide reacts with oxide and forms the metal and SO2
2 Cu2O + Cu2S → 6 Cu + SO2
26. Suggest some methods to prevent corrosion of metals. (AS1) 2 Marks
A: Corrosion of metals can be prevented by
(i) The surface of the metal is coated with paint or oil greasing
(ii) The surface of the metal is coated with a metal which is not be oxidised easily. This is called electro plating method.
(iii) An electro chemical method is to provide a sacrificial electrode of another metal (like mg. Zn etc) which corrodes it self but saves the object.
27. Write the formula of rust (AS1) 1 Mark
A: Fe2O3. × H2O
