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Download 9th Class Chemistry Notes (Unit # 7) for Federal Board (FBISE) Islamabad

Download 9th Class Chemistry Notes (Unit # 7) for Federal Board (FBISE) Islamabad

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Download 9th Class Chemistry Notes (Unit # 7) for Federal Board (FBISE) Islamabad

REVIEW QUESTION
What is oxidation state?
Oxidation state or oxidation number is defined as the number of charges an atom will have in a molecule or a compound.
Identify reducing agent in the following reaction.
CuO + H2 ---------------->  Cu + H2O
Because the oxidation number of Cu decreases (+2 to 0), so CuO3 is an oxidizing agent. Similarly the oxidation number of H increases (0 to +2), therefore H2 is reducing agent.
Write chemical reactions that occur in Nelson's cell.
At anode (Oxidation):
2Cl- ----------------> Cl2 + 2e-
At cathode (Reduction):
2H2O + 2e- ----------------> H2 + 2OH-
Why tin plated steel is used to make food cans?
Food and beverages industries use tinplated steel cans because the components of food beverages and the preservatives contain organic acids or their salts. They may form toxic substances by reacting with iron. These acids and salts are corrosive. Tin plating is nonpoisonous and prevents corrosion.
Explain one example from daily life which involves oxidation reduction reaction?
Redox in photography:
·        A photographic film is basically an emulsion of silver bromide, (AgBr) in gelatin.
·        When the film is exposed to light, silver bromide granules become activated.
·        Exposed film is placed in the developer solution (Hydroquinone) that is actually a reducing agent.
·        In hydroquinone the activated granules of silver bromide are reduced to black metallic silver.
·        Inactivated silver bromide is removed from the film by using a solvent (Sodium thiosulphate) called a fixer.
·        The areas of the film exposed to the light appear darkest because they have the highest concentration of metallic silver.
·        Thus photography involves oxidation-reduction reaction.

Define oxidation and reduction in terms of loss or gain of oxygen or hydrogen.
Oxidation:                                                           Reduction
Gain of oxygen                                            Loss of oxygen
Loss of hydrogen                                         Gain of hydrogen

Define oxidation and reduction in terms of 1055 or gain of electrons.
Oxidation:
A process that involves the loss of electrons by an element is called oxidation.
Na ---------------->  Na+ + e-
Ca ---------------->  Ca+2 + 2e-
Reduction:
A process that involves the gain of electrons by a substance is called reduction.
Cl + e- ---------------->  Cl-
O + 2e- ---------------->  O-2
List the possible uses of electrolytic cell.
·        Down's Cell is used for the commercial preparation of sodium metal. It produces chlorine gas as by product.
·        Nelson's Cell is used for the commercial preparation of sodium hydroxide. It also produces chlorine and hydrogen gas as by product.
·        Electrolytic cells are used for the commercial preparation of calcium and magnesium metals.
·        It is used to produce aluminum metal commercially.
·        It is used for the purification of copper.
·        Electrolytic cells are used to electroplate metals such as tin, silver, nickel etc.
·        Electrolytic cells are used to prepare anodized aluminum. Anodized aluminum can absorb dyes.
Describe how a battery produces electrical energy.
·        A battery is a galvanic cell or a group of galvanic cells joined in series.
·        It generates electric current by a redox reaction.
·        When connected in a circuit its anode oxidizes by releasing electrons.
·        These electrons through the external circuit begin to flow towards the cathode.
·        At cathode these electrons reduce oxidizing agent present in the electrolyte.
Describe the method of recovering metal from its ores.
·        The process of producing a metal from its ores, always involves oxidation reduction reaction.
·        Most of the metals are found in nature as oxides or sulphide ores.
·        After mining the ore, desired mineral is separated from the other materials.
·        Purified metal oxides are reduced to free metals by using a reducing agent.
Explain electrolytic refining of copper.
·        The copper metal obtained from its ores is usually impure.
·        It contains impurities such as zinc, iron, silver and gold. These impurities are removed by the process of electrolysis.
·        In this process impure copper bars act as anode and pure copper bars as cathode.
·        CuSO4 solution containing little sulphuric acid is used as the electrolyte.
Working:
·        On passing electricity copper anode dissolves forming Cu+2 ions.
·        Cations move towards the cathode at which only Cu+2 ions are reduced.
·        Thus pure copper deposits at cathode.
·        The less electropositive metals silver and gold fall to the bottom of the cell.
·        Copper obtained in this process is 99.5% pure.
·        Following reaction occur in this process:
At anode:
Cu ---------------> Cu+2 + 2e-
At cathode:
Cu+2 + 2e- ---------------> Cu

Explain how food and beverage industries deal with corrosion.
·        Tin plated steel is used to make cans.
·        Food and beverages industries use tin-plated steel cans. This is because the components of food beverages and the preservatives contain organic acids or their salts. They may form toxic substances by reacting with iron. These acids and salts are corrosive.
·        Tin plating is nonpoisonous and prevents corrosion.

Differentiate between Electrolytic and Galvanic Cell. 
Electrolytic Cell:
·        Electrical energy is converted into chemical energy.
·        Current is used to drive chemical reaction.
·        Non-Spontaneous oxidation-reduction reaction takes place.
·        Electrolysis takes place.
·        Examples are Down’s cell, Nelson’s cell
Galvanic Cell:
·        Chemical energy is converted into electrical energy.
·        Current is produced due to chemical reaction.
·        Spontaneous oxidation-reduction reaction takes place.
·        Electronic Conduction takes place.
·        Examples are Daniel cell, fuel cell.

Define oxidation number or oxidation state.
·        Oxidation state or oxidation number is defined as the number of charges an atom will have in a molecule or a compound.
·        The elements that show an increase in oxidation number are oxidized. The elements that show a decrease in oxidation number are reduced

Find the oxidation state of nitrogen in the following compounds. (i) NO2 (ii) N2O (iii) N2O3 (iv) HNO3
Oxidation number of N in NO2:
The sum of oxidation numbers must be zero.
[Oxidation No. of N] + 2[Oxidation No. of O] =      0
[Oxidation No. of N] + 2[-2]                                 =      0
[Oxidation No. of N] - 4                               =      0
[Oxidation No. of N]                                    =      +4

Oxidation number of N in N2O:
The sum of oxidation numbers must be zero.
2[Oxidation No. of N] + [Oxidation No. of O] =      0
2[Oxidation No. of N] + [-2]                        =      0
2[Oxidation No. of N] - 2                             =      0
2[Oxidation No. of N]                                  =      2
[Oxidation No. of N]                                   =      2/2    =      +1


Oxidation number of N in N2O3:
The sum of oxidation numbers must be zero.
2[Oxidation No. of N] + 3[Oxidation No. of O]         =      0
2[Oxidation No. of N] + 3[-2]                               =      0
2[Oxidation No. of N] – 6                            =      0
2[Oxidation No. of N]                                  =      6
[Oxidation No. of N]                                   =      6/2    =      +3

Oxidation number of N in HNO3:
The sum of oxidation numbers must be zero.
[Oxidation No. of H] + [Oxidation No. of N] + 3[Oxidation No. of O]  =      0
[+1] + [Oxidation No. of N] + 3[-2]                                               =      0
+1 + [Oxidation No. of N] – 6                                                       =      0
[Oxidation No. of N] – 5                                                               =      0
[Oxidation No. of N]                                                                    =      5

Find the oxidation state of S in the following compounds. (a) H2S (b) H2SO3 (c) Na2S2O3
Oxidation number of S in H2S:
The sum of oxidation numbers must be zero.
[Oxidation No. of S] + 2[Oxidation No. of H]   =      0
[Oxidation No. of S] + 2[+1]                        =      0
[Oxidation No. of S] + 2                              =      0
[Oxidation No. of S]                                     =      -2

Oxidation number of S in H2SO3:
The sum of oxidation numbers must be zero.
2[Oxidation No. of H] + [Oxidation No. of S] + 3[Oxidation No. of O] =      0
2[+1] + [Oxidation No. of S] + 3[-2]                                              =      0
+2 + [Oxidation No. of S] – 6                                                       =      0
[Oxidation No. of S] – 4                                                               =      0
[Oxidation No. of S]                                                                     =      +4

b: Oxidation number of Sin Na2S2O3:
The sum of oxidation numbers must be zero.
2[Oxidation No. of Na] + 2[Oxidation No. of S] + 3[Oxidation No. of O]       =      0
2[+1] + 2[Oxidation No. of S] + 3[-2]                                            =      0
+2 + 2[Oxidation No. of S] – 6                                                      =      0
2[Oxidation No. of S] – 4                                                              =      0
2[Oxidation No. of S]                                                                   =      4
[Oxidation No. of S]                                                                     =      4/2
                                                                                                =      +2



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Download Class Notes: Download 9th Class Chemistry Notes (Unit # 7) for Federal Board (FBISE) Islamabad
Download 9th Class Chemistry Notes (Unit # 7) for Federal Board (FBISE) Islamabad
Download 9th Class Chemistry Notes (Unit # 7) for Federal Board (FBISE) Islamabad
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