Match the following: Group-A Group-B (i) Corrosion (a) Lanthanides (ii) Gold sol (b) Used in treatment of cancer (iii) Radon (c) Purple of cassius (iv) f-block elements (d) Barbituric acid (v) Tranquilizers (e) Hydrated ferric oxide.

(i)-(e), (ii)-(c), (iii)-(b), (iv)-(a), (v)-(d)

(i)-(d), (ii)-(c), (iii)-(b), (iv)-(a), (v)-(e)

(i)-(e), (ii)-(b), (iii)-(c), (iv)-(a), (v)-(d)

(i)-(e), (ii)-(a), (iii)-(b), (iv)-(c), (v)-(d)

What is electrochemical series? Describe kohlrausch's law and give its two applications.

Electrochemical series is defined as the arrangement of elements in order of their increasing electrode potential values. The series has been established by measuring the potential of various electrodes versus standard hydrogen electrode. Kohlrausch’s law states that the equivalent conductivity of an electrolyte at infinite dilution is equal to the sum of the conductances of the anions and cations. The molar conductivity of a solution at a given concentration is the conductance of the volume of solution containing one mole of electrolyte kept between two electrodes with the unit area of cross-section and distance of unit length. The molar conductivity of a solution increases with the decrease in concentration. This increase in molar conductivity is because of the increase in the total volume containing one mole of the electrolyte. When the concentration of the electrolyte approaches zero, the molar conductivity is known as limiting molar conductivity. Applications of Kohlrausch's law: (i) Kohlrausch law helps us in the determination of limiting molar conductivities for any electrolyte. (ii) This law also helps us in determining the value of dissociation constant from the value of molar conductivity and limiting molar conductivity for a weak electrolyte at a given concentration.

What is corrosion? Explain its mechanism and write any two measures of its prevention.

Corrosion is defined as a natural process that causes the transformation of pure metals into undesirable substances when they react with substances like water or air. This reaction causes damage and disintegration of the metal starting from the portion of the metal exposed to the environment and spreading to the entire bulk of the metal. Rusting of iron is an example of corrosion. Mechanism of rusting of iron: Rusting of iron which is the most commonly seen example happens when iron comes in contact with air or water. The reaction could be seen as a typical electrochemical cell reaction. Here metal iron loses electrons and gets converted to Fe 2 + . The electrons lost will move to the other side where they combine with H + ions. These ions are either released by H 2 O or H 2 CO 3 present in the atmosphere. H 2 O → H + + OH - H 2 CO 3 → 2 H + + CO 3 2 - The Hydrogen thus formed by the reaction of H + and electrons react with oxygen to form H 2 O . Two methods that are used for the prevention of corrosion are electroplating and galvanization.

What is electrochemical cell? Explain its working with the help of diagram.

An electrochemical cell is a device that can generate electrical energy from the chemical reactions occurring in it, or use the electrical energy supplied to it to facilitate chemical reactions in it. A common example of an electrochemical cell is a standard 1 . 5 V cell which is used to power many electrical appliances such as TV remotes and clocks. The electrochemical cell is also called as galvanic cell. In a galvanic cell oxidation-reduction reactions are responsible for the production of current. These reactions take place in two separate compartments. Each compartment consists of a suitable electrolytic solution and an electric conductor dipped in it. The electrical conductor in contact with the solution of electrolyte is called an electrode. Each compartment containing the electrode and electrolyte is called a half cell. When the two half cells are coupled a galvanic cell is constructed. External connection between the half cells is provided by copper wires through a voltmeter while internal connection is provided by a salt bridge. In a Daniel cell, one half cell consists of a solution of zinc sulphates a zinc rod, while the other half cell consists of a solution of copper sulphate and a copper electrode. The two half cells are connected by KCl salt bridge. On connecting the two rods, zinc rod dissolves to form Zn 2 + ion which goes into solution. Thus, oxidation takes place at the zinc anode Zn ( s ) → Zn 2 + ( aq ) + 2 e - Electrons produced at the zinc electrode flow through copper wire and the Cu -electrode into CuSO 4 solution. Copper ions in the solution are reduced and copper is deposited on the cathode. Thus, reduction takes place at the copper electrode. Cu 2 + ( aq ) + 2 e - → Cu ( s ) In the outer circuit electron flows from zinc rod to copper rod. The conventional current flow is on opposite direction to that of flow of electrons.

What is standard hydrogen electrode? Explain with diagram.

Standard hydrogen electrode is used to measure the electrode potentials of other half-cells. It is assigned a potential of zero volts at all temperatures. The potential corresponds to the reaction H + ( aq ) + e - → 1 2 H 2 ( g ) As the potential of single half-cell cannot be measured experimentally, standard hydrogen electrode is used to measure the potential of the required half-cell. The electrode potential of a half cell is equal to the measured emf of the cell in which one electrode is SHE. Standard hydrogen electrode consists of a platinum electrode coated with platinum black. This electrode is dipped in a solution of acid of unit molarity and pure H 2 gas is bubbled through it at atmospheric pressure. The electrode thus refers to the following half cell: Pt ( H 2 , g , 1 atm ) | H + ( aq , 1 . 0 mol L - 1 ) In the half cell reaction platinum acts as catalyst. The equilibrium half cell reaction is written as, 1 2 H 2 ( g , 1 atm ) ⇌ H + ( aq , 1 . 0 mol L - 1 ) + e - and E ⊝ ( H + / H 2 ) = - E ( H 2 / H + ) = - ∆ G / F = 0 By convention the SHE is assigned a zero electrode potential.

If the concentration of copper sulphate solution is 0 . 01 M and that of zinc sulphate solution is 0 . 1 M , then calculate the emf of Daniel cell at 298 K . E cell ° = 1 . 1 V

Emf is defined as the maximum potential difference between two electrodes of galvanic cell. Given concentration of copper sulphate solution is 0 . 01 M Also, given the concentration of zinc sulphate solution is 0 . 1 M . By using Nernst equation, we know that E cell = E cell ° - 0 . 059 2 log Zn 2 + Cu 2 + E cell = 1 . 1 - 0 . 059 2 log 0 . 1 0 . 01 E cell = 1 . 1 - 0 . 029 log 10 E cell = 1 . 07 V

When iron rod is displaced in CuSO 4 solution, copper is displaced but when copper rod is dipped in FeSO 4 solution, iron does not get displaced. Explain why.

When copper rod is dipped in iron sulphate solution, iron does not get displaced because as per the electrochemical series, the reduction potential of copper is higher than that of iron. To replace a metal in a solution, the reduction potential must be less than the other substance. Also, iron is more reactive than copper. Hence, iron replaces copper in copper sulphate solution and copper cannot displace iron in iron sulphate solution.

Calculate the electromotive force (e.m.f) for the following cell reaction Zn + 2 Ag + → Zn 2 + + 2 Ag Where the values of E ° Zn 2 + Zn and E ° Ag + Ag are respectively - 0 . 76 V , + 0 . 80 V .

Electromotive force is defined as the maximum potential difference between two electrodes of a galvanic cell. Given reaction is Zn + 2 Ag + → Zn 2 + + 2 Ag We know that, E cell ° = E cathode ° - E anode ° E cell ° = 0 . 80 - - 0 . 76 = 1 . 56 V

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