Azhar Exam CH4

Azhar Exam CH4 Electrochemistry
A) Write the scientific term for the following:

1- An electrochemical process in which the metal needs to be protected from
corrosion by coating with a more active metal.
2- A short expression which represents the oxidation and reduction reactions that
happen at each of the anode and the cathode.
3- The masses of the different materials formed or consumed by the same amount
of electricity are directly proportional to their equivalent masses.
B) Choose the correct answer:
1- On a rod of an element (A) is placed in a solution of ions of an element (B) If you
know that (A) is divalent, (B) is monovalent. Which of the following is true ?
a. Number of dissolved moles of (A) is double the number of precipitated moles of
(B).
b. Number of dissolved moles of (A) is half the number of precipitated moles of (B).
c. Number of dissolved moles of (A) equals the number of precipitated moles of (B).
d. Number of dissolved moles of (A) is three times the number of precipitated moles
of (B).
2- On adding potassium dichromate solution acidified by sulphuric acid to iron (II)
sulphate solution, so the correct equation that expresses the oxidation reduction
reaction is
a. Fe2+(q) + Cr2O72-(aq) + 14H+(aq)→ Fe3+(aq) + 2Cr3+(aq) + 7H₂O(l)
b. 6Fe2+(q) + Cr2O72-(aq) + 14H+(aq)→ 6Fe3+(aq) + 2Cr3+(aq) + 7H₂O(l)
c. Fe2+(q) + Cr2O72-(aq) + 14H+(aq)→ Fe3+(aq) + 2Cr3+(aq) + 7H₂O(l)
d. 6Fe2+(q) + Cr2O72-(aq) + 14H+(aq)→ 6Fe3+(aq) + 2Cr3+(aq) + 7H₂O(l)
3- On connecting lead accumulator to an external source of electricity its emf = 14 V.
Which one of the following choices is correct?
a. Decreasing the pOH value of electrolyte.
b. Decreasing the pH value of electrolyte.
c. Increasing oxidation number of lead at anode.
d. Increasing the quantity of water in battery.
4- On putting a metal (X) in the salt solution YCl₂, the concentration of cations Y²+ is
changed from 0.1 M to 0.01 M Which of the following exist in the solution?
a. Ions of X2+, Y²+ and Cl-
b. Ions of X2+, Cl- only.
c. Ions of Y²+ and Cl-, X is precipitated at the bottom of the vessel.
d. Ions of C l-,X and Y are precipitated at the bottom of the vessel.
5- In the galvanic cell which illustrated by the following diagram:
Zn(s)/Zn2+(aq) // Pb2+(aq)/Pb(s)
On adding drops from HCl(aq) to both half cells. Which of the following choices is
correct?
a. Increasing conc. of Pb2+(aq) ions.
b. emf value for the cell increase.
c. Time for consuming battery decrease.
1
d. Decrease cone of Zn2+(aq) ions.
6- If you know that:
Al0→ Al3+ + 3e- E° = 1.67 V
Cu2+ + 2e-→Cu0 E = 0.34 V
The diagram of the cell composed of these two electrodes is
a. Al0/Al3+ // Cu2+/Cu0
b. 3Cu0/3Cu2+ //2Al³+/2Al0
c. 2Al0/2Al3+//3Cu2+/3Cu0
d. Cu2+/Cu0//Al3+/Al0
7- In Daniell cell zinc half-cell is replaced by silver half-cell. Which of the following is
correct? [E0Zn=0.76 V.E0Ag=-0.8 V ]
a. The value of e.m.f decreases, the current direction does not change.
b. The value of e.m.f increases, the current direction changes.
c. The value of e.m.f decreases, the current direction changes.
d. The value of e.m.f increases, the current direction does not change.
8- The quantity of electricity that required to evolve 1.204 x 1023 molecules of oxygen
gas on electrolysis of acidified water is
a. 0.8 F b. 0.4 F c. 9650 C d. 19300 C
9- Three rods of different elements (A, B and C) are put in HCl(aq), (A) and (B) react,
while (C) doesn't react, when a rod of element (A) is put in a solution contains ions
of element (B), it is corroded.
So the arrangement of these elements according to their oxidation potential
a. A>B>C b. B>A>C c. C>B>A d. A>C>B
10- On dipping a magnesium strip in silver nitrate solution, the following reaction is
occurred:
Mg(s) + 2AgNO3(aq) →Mg(NO3)2(aq) + 2Ag(s)
Which of the following properly expresses what happens?
a. Oxidation of magnesium and reduction of silver ions.
b. Oxidation of magnesium and oxidation of silver.
c. Reduction of magnesium and oxidation of silver.
d. Reduction of magnesium and reduction of silver ions.
11- A galvanic cell is expressed by the following cell diagram:
Fe0/Fe2+ // Ni2+ / Ni0 if:
Fe(s)→Fe2+(aq) + 2e- E°=+0.409 V
Ni2+(g)+2e-→Ni(s) E°=-0.23 V
Then the e.m.f of the cell is
a. 1.639 V b. 0.936 V c. 0.396 V d. 0.179 V
C) Write scientific explanation for the following:
1- Adding cryolite melt containing a little of fluorspar to bauxite in extraction process
of aluminum
2- The presence of salts in water increases the rate of rusting process and metal
corrosion
3- The erosion of the anode in the galvanic cell.
2
4- Mercury cell is an alkaline, whereas the lead-acid battery is an acidic.
D) 1. The given diagram represents the process of purifying copper metal :

(1) What happens to the electrode (A) ? Write the equation of the reaction occurring
at it.
(2) What happens to the silver found in the impure copper electrode ? Explain.
2. Calculate the concentration of silver ions Ag+ [Ag = 108] in 0.25 L solution of it, if
they are completely consumed in electroplating a spoon using 2A electric current for
2.3 minutes.

Azhar Exam CH4

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Azhar Exam CH4 Electrochemistry

A) Write the scientific term for the following:

D) 1. The given diagram represents the process of purifying copper metal :

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