Rusting of iron is quicker in saline water than in ordinary water. Explain.

Saline water contains greater number of irons (dissolved salts, NaCl) than ordinary water and therefore electro-chemical reaction is quicker with saline water than when ordinary water is present. This increases rate of corrosion of metal.
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Can a nickel spatula be used to stir the solution of CuSO4? Support your answer with reason. (E°Ni2+/Ni = – 0.25 V, E°Cu2+/Cu = + 0.34 V)


No.nickel spatula cannot be used  to stir the solution of CuSO4

As E° Ni2+/Ni < E°cu2+/cu

Nickel has more tendency to lose electrons than copper. If a nickel spoon is used to CuSO4solution, it will displace Cu from CuSO4 solution.

Ni(s) + Cu2+ (aq) → Ni2+ (aq) + Cu(s)

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What is corrosion? What are the factors which affect corrosion?


Corrosion is the process of slowly eating away of the metal due to attack of the atmospheric gases on the surface of the metal resulting into the formation of compounds such as oxides, sulphides, carbonates, etc. The corrosion of iron is called rusting.

The phenomenon of corrosion involves the destruction of metal in which metal is generally converted into oxide. Common examples are rusting of rion, tarnishing of silver and deposition of green coating on copper and bronze.

Factors affecting corrosion:
(a) Presence of oxygen, sulphur etc. (elements which gain electrons).
(b) Presence of moisture.
(c) Presence of carbon dioxide.

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The standard reduction potential for the Zn2+ (aq) | Zn(s) half cell is 0.76 V. Write the reactions occurring at the electrodes when coupled with standard hydrogen electrode (SHE).

Zn acts as anode, and SHE acts as cathode
At anode: Zn(s) → Zn2+ (aq) + 2e
At cathode: 2H+ (aq) + 2e H2(g)
The net cell reaction is
Zn(s) + 2H+ (aq) → Zn2+ + H2(g)

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CO2 is always present in natural water. Explain its effect (increases, stops or no effect) on rusting of iron.

CO2 increases rusting of iron: CO2 present in water is in the form of H2CO3. H2CO3dissociates into H+ and HCO3-.

H2CO3 = HCO3-+H+H2O = H++OH-2H++2e  H2

Hydroxyl ion or bicarbonate ions attack the iron surface to form anodic regions in which iron loses electrons and pass on to ferrous sulphate which is further oxidised to ferric state by oxygen of the air. The released electrons move towards the cathode region where H+ions are converted into hydrogen gas.

Fe Fe2++2e-O2 = 2H2O + 4e-  4OH-4Fe+3O2+2×H2O  2 Fe2O3. XH2O

Thus CO2 increases rusting because H2COgives H+ which gain electrons to form H2 gas. The electrons are released by iron.
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