Sample Solution

1. Discuss the effect of pressure on the solubility of gases. How is Henry’s law constant determined?
2. Draw and explain the mutual solubility curve of nicotine-water system. Which other system exhibits the similar curve?
3. (a) What are conjugate solutions? Give one example.
   (b) Define metastable equilibrium and differentiate it from true equilibrium
4. Define any five of the following terms :
   (i) A component
   (ii) Mole fraction
   (iii) Incongruent melting compounds
   (iv) Liquid junction potential
   (v) Ionic mobility
   (vi) Conductometric titration
5. (a) Give the mathematical expression for Gibbs’ phase rule and calculate the maximum number of phases that can coexist for a one-component system.
   (b) Draw the phase diagram for sulphur system and label the sublimation and fusion curves for monoclinic sulphur on it.
6. (a) How does $\mu \mathrm{vs}$$\mu \mathrm{vs}$muvs\mu \mathrm{vs}$\mu \mathrm{vs}$. T curves for a pure substance get affected by an increase in pressure? Draw a schematic diagram indicating the same?
   (b) Two substances, X and Y form a simple eutectic system. The melting point of X is more than that of $Y$$Y$YY$Y$ and a mixture of $X$$X$XX$X$ and $Y$$Y$YY$Y$ having $40\mathrm{\%}$$40\mathrm{\%}$40%40 \%$40\mathrm{\%}$ of $X$$X$XX$X$ form the eutectic mixture having a melting point of 512 K . Based on this information, draw a schematic suitably labelled phase diagram for the system.
7. (a) Explain the concentration dependence of molar conductivity for a strong electrolyte

9. (a) Outline the requirements for the construction of concentration cells without transference.
   (b) The cell reaction for a galvanic cell is given below:

Answer:

Question:-1

Discuss the effect of pressure on the solubility of gases. How is Henry’s law constant determined?

Answer:

"At a constant temperature, the partial pressure of a gas over a solution is directly proportional to the concentration of the gas in the solution."

Mathematical Expression of Henry’s Law:

• $p$$p$pp$p$ is the partial pressure of the gas over the solution (in units of pascals, Pa),
• $x$$x$xx$x$ is the solubility of the gas in the liquid, typically expressed as the mole fraction of the gas in the solution,
• $k_H$$k_H$k_(H)k_H$k_H$ is the Henry’s law constant, a constant specific to the gas-solvent combination at a given temperature.

Determining the Henry’s Law Constant:

1. Experimental Approach:
   • A series of experiments are conducted where the solubility of the gas is measured at different known pressures.
   • For each pressure value, the corresponding solubility $x$$x$xx$x$ (often measured as the mole fraction of the gas in the liquid) is determined.
2. Plotting the Data:
   • A plot is made with the partial pressure $p$$p$pp$p$ on the y-axis and the solubility $x$$x$xx$x$ (mole fraction) on the x-axis.
   • According to Henry’s law, this plot should yield a straight line, and the slope of the line gives the value of $k_H$$k_H$k_(H)k_H$k_H$.
3. Extrapolation:
   • The Henry’s law constant is determined by extrapolating the graph to $x=0$$x=0$x=0x = 0$x=0$, which gives the ratio $p/x$$p/x$p//xp/x$p/x$ as a constant.
4. Mathematical Expression of $k_H$$k_H$k_(H)k_H$k_H$:
   From the equation $p=k_H\cdot x$$p=k_H\cdot x$p=k_(H)*xp = k_H \cdot x$p=k_H\cdot x$, the Henry’s law constant can be calculated as:

Example:

Non-Ideal Solutions:

Question:-2

Draw and explain the mutual solubility curve of nicotine-water system. Which other system exhibits the similar curve?

Answer:

Mutual Solubility Curve for Nicotine-Water System:

1. At Low Temperatures:
   At lower temperatures, both nicotine and water have relatively low mutual solubility. The water cannot dissolve much nicotine, and nicotine is not highly soluble in water either.
2. At High Temperatures:
   As the temperature increases, the solubility of both water in nicotine and nicotine in water increases. Both components dissolve more readily as the temperature rises.
3. Critical Point (Cloud Point):
   The curve has a characteristic "cloud point," which is the temperature at which both substances start to form a homogeneous solution. Below this temperature, they separate into two immiscible phases. Above this point, they become completely miscible in each other.
4. Shape of the Curve:
   The mutual solubility curve typically has a concave shape where the solubility of both substances increases with increasing temperature. There’s a point where both substances are completely miscible at higher temperatures and separate at lower temperatures.

Explanation:

• The mutual solubility of nicotine and water is temperature-dependent. Below a certain temperature, nicotine and water are immiscible, meaning they do not form a homogeneous solution and tend to separate into two phases (a nicotine-rich phase and a water-rich phase).
• As the temperature increases, the solubility of each substance in the other increases, and above a certain temperature, the system becomes completely miscible, forming a single homogeneous solution.
• The critical temperature is the temperature beyond which the two substances are completely miscible and no phase separation occurs.

Similar Systems:

• Phenol-Water System:
  Like nicotine and water, phenol and water are partially miscible at lower temperatures but become completely miscible at higher temperatures. The mutual solubility curve for phenol and water also shows a critical temperature point at which they become fully miscible. Below this point, phenol and water separate into two phases, just like the nicotine-water system.

Question:-3(a)

What are conjugate solutions? Give one example.

Answer:

Example of Conjugate Solutions:

1. Acetic acid (CH₃COOH) – a weak acid that partially dissociates in water.
2. Acetate ion (CH₃COO⁻) – the conjugate base of acetic acid.

• The acetic acid is the acid (proton donor).
• The acetate ion is its conjugate base (proton acceptor).