28
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29
(c) Zn granules turned green (d) No reaction occurs
Rohit observed the formation of a coating when he added the solution of copper sulphate to the 1
iron nails. This deposition is of :
(a) Iron
(b)
Copper
(C) Iron sulphide
(d) Sulphur
If the metals A, B, C and D are arranged on the basis of their reactivity as A >B>C> D, then
the statement which will not hold good will be :
(a) 'D' cannot displace C from its salt solution.
(b) A can displace B from its salt solution.
(C) A will not react with C.
(d) B can undergo oxidation when placed in a salt solution of D.
When two resistors of resistance 3 1 and 52 are connected to a battery, it will have across the
two resistors :
Same potential difference when connected in series
Same current when connected in parallel
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30
Answers
Answer:
The term oxidation was first used to describe reactions in which metals react with oxygen in air to produce metal oxides. When iron is exposed to air in the presence of water, for example, the iron turns to rust—an iron oxide. When exposed to air, aluminum metal develops a continuous, transparent layer of aluminum oxide on its surface. In both cases, the metal acquires a positive charge by transferring electrons to the neutral oxygen atoms of an oxygen molecule. As a result, the oxygen atoms acquire a negative charge and form oxide ions (O2−). Because the metals have lost electrons to oxygen, they have been oxidized; oxidation is therefore the loss of electrons. Conversely, because the oxygen atoms have gained electrons, they have been reduced, so reduction is the gain of electrons. For every oxidation, there must be an associated reduction. Therefore, these reactions are known as oxidation-reduction reactions, or "redox" reactions for short.
Explanation:
Each neutral oxygen atom gains two electrons and becomes negatively charged, forming an oxide ion; thus, oxygen has an oxidation state of −2 in the product and has been reduced. Each neutral aluminum atom loses three electrons to produce an aluminum ion with an oxidation state of +3 in the product, so aluminum has been oxidized. In the formation of Al2O3, electrons are transferred as follows (the small overset number emphasizes the oxidation state of the elements):
Equation 4.4.1 and Equation 4.4.2 are examples of oxidation–reduction (redox) reactions. In redox reactions, there is a net transfer of electrons from one reactant to another. In any redox reaction, the total number of electrons lost must equal the total of electrons gained to preserve electrical neutrality. In Equation 4.4.3 , for example, the total number of electrons lost by aluminum is equal to the total number gained by oxygen: