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Class/Subject: 9th Class Chemistry
Chapter Name: Electrochemistry
Board: Federal Board
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FBISE 9th Class Chemistry Chapter 7 Electrochemistry Short Questions Answers
The branch of chemistry that deals with the relationship between electricity and chemical reactions are called electrochemistry.
Oxidation is defined as the gain of oxygen atoms or loss of hydrogen atoms by an element.
Acetylene (C2H2) is commercially used for cutting and welding metals. When acetylene burns, it produces a very hot flame known as oxy-acetylene flame.
Reduction is defined as the removal of oxygen or addition of hydrogen or gain of electron or decrease in oxidation number during a chemical reaction.
Oxidation state or oxidation number is defined as the number of charges an atom will have in a molecule of a compound.
An oxidizing agent is a reactant containing the element that is reduced (gains electrons) in a chemical reaction.
A reducing agent is a reactant containing the element that is oxidized (loses electrons) in the chemical reaction.
Such a reaction that involved the transfer of electrons is known as an oxidation-reduction reaction. These reactions are also called redox reactions.
Devices that convert chemical energy into electrical energy or vice versa are called electrochemical cells.
An electrochemical cell that uses electrical energy to drive a chemical reaction is called an electrolytic cell.
An electrochemical cell that converts chemical energy into electrical energy is called a galvanic cell.
The reaction that takes place of its own, without any external assistance is called spontaneous reaction.
The reaction which is the reverse of a spontaneous reaction and takes place by supplying energy to the system from an external source is called a non-spontaneous reaction.
The apparent charge on an atom, ion, or molecule is called valency, is written as the sign followed by the number i.e. 2+.
The substances, which can conduct electricity in their solutions or molten states, are called electrolytes. For example, solutions of salts, acids, or bases are good electrolytes.
The electrolytes which ionize completely in an aqueous solution and produce more ions are called strong electrolytes. For example, NaCl, NaOH, H2SO4, are strong electrolytes.
Chemical species which carry a positive charge. E.g. Na+, K+, etc.
Chemical species carry a negative charge. E.g. O2-, Cl-, etc.
A galvanic cell consists of two cells one having a cathode while the other having anode end which is connected with a salt bridge. Each of these is known as a half cell.
Salt-bridge is a U-shaped glass tube that consists of a saturated solution of strong electrolyte supported in a jelly-type material. The ends of the U-shaped glass tube are sealed with a porous material like glass wool. The function of the salt bridge is to keep the solutions of two half cells neutral by providing a pathway for the migration of ions.
It is a redox reaction that takes place by the action of air and moisture with metals. For example, rusting of iron.
It is a redox reaction that takes place when the iron is exposed to air and moisture. The chemical formula of rust is Fe2O3 H2O.
Alloy is a homogeneous mixture of one metal with one or more metals or nonmetals. For example, stainless steel is an alloy of iron, chromium, and nickel.
i. Normal oxides -2
ii. Peroxides -1
iii. OF2 +2
This electrolytic cell is a circular furnace. In the center, three is a large block of graphite, which acts as an anode while the cathode around it is made of iron.
The process of coating a thin layer of zinc on iron is called galvanizing.
The principle of electroplating is to establish an electrolytic cell in which anode is made of the metal to be deposited and cathode of the object on which metal is to deposit. The electrolyte is an aqueous solution of a salt of the respective metals.
They are made from steel with a thin coating of tin to prevent corrosion. Tin plated steel I used to make cans. The food and beverage industries use tin-plated steel cans. This is because the components of food beverages and preservatives contain organic acids or salts. They may from toxic substances by reacting with iron. Tin plating is non-poisonous and prevents corrosions.
i. Down’s cell is used for the commercial preparation of sodium metal. It produces chlorine gas as a by-product.
ii. Nelson’s cell is used for the commercial preparation of sodium hydroxide.
iii. It is used for the purification of copper.
Electrons leave the Zn-electrode and then move towards Cu-electrodes.
A battery is a galvanic cell or a group of galvanic cells joined in series. It generates an electric current by a redox reaction. When connected in a circuit its anode oxidizes by releasing electrons. These electrons through the external circuit are to flow towards the cathode. At the cathode, these electrons reduce oxidizing agent present in the electrolyte.
Aluminum corrodes but it does not rust. Rust refers only to iron and steel corrosion. A very hard material aluminum oxide protects the aluminum from further corrosion. In comparison to that when iron corrodes. Its color changes and produces large red flakes known as rust. Unlike aluminum oxide, the expanding and flaking of rust exposes the new metal to further rusting.
The free electrons move through iron sheets; until they reach a region of relatively high oxygen concentration, near the surface surrounded by a water layer. This region acts as a cathode and electrons reduce the oxygen molecule in the presence of H+ ions.
O2 + 4H+ → 2H2O
In Nelson’s cell, the cathode is internally lined with the asbestos diaphragm. The cathode is a U-shaped perforated iron from where sodium hydroxide solution slowly percolates in a catch basin.
SO2 + 2H2S → 2H2O + 3S
As hydrogen is removal from H2S, therefore H2S is oxidized, while removal of oxygen takes place in SO2, therefore SO2 is reduced.
FeO Co → Fe + CO2
When FeO reacts with CO, oxygen is removed from FeO which shows a reduction process. On the other hand, when oxygen is added to CO it shows an oxidation process. Therefore, it is a complete redox reaction.
As a result of the redox reaction, an electric current is produced. The batteries which are used for starting automobiles, running calculators and toys, and to lit the bulbs work on the same principle.
Anodized aluminum sheets are widely used in buildings nowadays. Anodized aluminum can absorb dyes. The dying of aluminum can produce metallic red, metallic blue, or other metallic colors on the metal surface.
The electrolytic process used to deposit one metal on another metal is called electroplating.
In Daniel’s cell, the electron takes to flow from the Zn electrode (anode) towards the cathode made up of copper through the external circuit.
The iron grill is painted frequently to protect it from rusting. The paint layer protects iron from the attack of moisture and oxygen.
In the electroplating of silver, Ag+ ions come from an anode while they deposit at the cathode.
In the electroplating of chromium, the anode is made of antimonial lead while the object to be electroplated acts as a cathode.
Volta (1745 – 1827) was an Italian physicist known especially for the development of the first electric cell in 1800.
It is an alloy that is made up of iron, chromium, and nickel. This does not corrode.