The resistance of a conductivity cell containing 0 . 001 M KCl at 298 K is 1500 Ω if the conductance of 0 . 001 M KCl at 298 K is 0 . 146 × 10 - 3 S cm - 1 , what is the cell constant?

Cell constant is defined as the ratio of the distance between the electrodes divided by the area of cross-section of the electrode Given that Resistance = 1500 Ω k = 0 . 146 × 10 - 3 We know that, k = Gx , where k = conductivity , G = 1 R , x = cell constant 0 . 146 × 10 - 3 = 1 1500 × x x = 0 . 146 × 10 - 3 × 1500 = 0 . 219 cm - 1

What is cell constant? What is the relation between specific conductivity and cell constant?

The ratio of the distance between the electrodes divided by the area of cross-section of the electrode is called as cell constant l A . It is denoted by the symbol, G * . The cell constant is usually determined by measuring the resistance of the cell containing a solution whose conductivity is already known. Specific conductance is defined as the conductance of a solution of definite dilution enclosed in a cell having two electrodes of unit area separated by one metre apart. The relation between specific conductance and cell constant is: k = l A × C where, k = specific conductance, C = cell constant.

The conductance of 0 . 025 mol L - 1 methanoic acid is 46 . 15 S cm 2 mol - 1 . Calculate its degree of dissociation and dissociation constant. Given that λ ° H + = 349 . 6 Scm 2 mol - 1 and λ ° HCOO - = 54 . 6 Scm 2 mol - 1

The degree of dissociation is the phenomenon of producing free ions carrying current , which at a given concentration is dissociated from the fraction of solute. Given: C = 0.025 m o l L - 1 ∧ m = 46.1 S c m 2 m o l - 1 λ 0 H + = 349.6 S c m 2 m o l - 1 λ 0 H C O O - = 54.6 S c m 2 m o l - 1 ∧ m 0 H C O O H = λ 0 H + + λ 0 H C O O - = 349.6 + 54.6 = 404.2 S c m 2 m o l - 1 Now, degree of dissociation: α = ∧ m H C O O H ∧ m 0 H C O O H = 46.1 404.2 = 0.114 Thus, dissociation constant: K = c ∝ 2 1 - ∝ = 0.025 m o l L - 1 0.114 2 1 - 0.114 = 0.025 m o l L - 1 0.114 2 0.886 = 3.67 × 10 - 4 m o l L - 1

Define Kohlrausch law.

Kohlrausch's law: This 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. If a salt is dissolved in water, the conductivity of the solution is the sum of the conductances of the anions and cations.

Write chemical equations for charging and discharging of lead storage cell.

Lead storage battery, also known as lead acid battery is the oldest type of rechargeable battery and is commonly used in automobiles and inverters. It consists of a lead that acts as anode and a grid of lead packed with lead dioxide that acts as cathode. Oxidation process that takes place during charging process. The chemical reactions that take place during charging process are: At cathode: PbSO 4 + 2 e - → Pb + SO 4 2 - At anode: PbSO 4 + 2 H 2 O → PbO 2 + SO 4 2 - + 4 H + + 2 e - Overall reaction is: 2 PbSO 4 + 2 H 2 O → PbO 2 + Pb + 2 H 2 SO 4 Reduction process takes place during the process of discharge. The chemical reactions that take place during discharging process is: At cathode: Pb + SO 4 2 - → PbSO 4 + 2 e - At anode: PbO 2 + SO 4 2 - + 4 H + + 2 e - → PbSO 4 + 2 H 2 O Overall reaction is: PbO 2 + Pb + 2 H 2 SO 4 → 2 PbSO 4 + 2 H 2 O 3

Define corrosion. Write two preventions from corrosion.

Corrosion: 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 a common example for the process of corrosion. Prevention of corrosion: Preventing corrosion is of utmost importance in order to avoid huge losses. The majority of the structures are made out of metals. This includes bridges, automobiles, machinery, household goods like window grills, doors, railway lines, etc. While this is a concerning issue, several treatments are used to slow or prevent corrosion damage to metallic objects. This is especially done to those materials that are frequently exposed to the weather, saltwater, acids, or other hostile environments. Some popular methods to prevent corrosion include are electroplating and galvanization.

Explain Kohlrausch law. Write in brief two applications of this law.

Kohlrausch law of independent migration of ions: The law states that at infinite dilution, each ion migrates independently of its co-ion and make its own contribution to the total molar conductivity of an electrolyte irrespective of the nature of other ion with which it is associated. The molar conductivity of the electrolyte at zero concentration is equal to the sum of molar conductivity of cation and the molar conductivity of anion at infinite dilution. Λ o = λ + o + λ - o Applications of Kohlrausch law: (i) Kohlrausch law helps us in the determination of limiting molar conductivities for any electrolyte. Weak electrolytes have lower molar conductivities and lower degree of dissociation at higher concentrations. (ii) Kohlrausch 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.

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Define the following and write the formula and unit :

Molar conductivity

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