GATE Life Sciences Chemical Equilibria Syllabus

Chemical Equilibria syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Chemical Equilibria in GATE Life Sciences, not a summary of it.

1. 1

   Osmotic pressure, elevation of boiling point and depression of freezing point

   3 topics

   • Osmotic Pressure
   • Elevation of Boiling Point
   • Depression of Freezing Point
2. 2

   Ionic Equilibria in Solution

   5 topics

   • Solubility Product
   • Common Ion Effect
   • Hydrolysis of Salts
   • pH
   • Buffer and Their Applications
3. 3

   Equilibrium Constants (Kc, Kp and Kx) for Homogeneous Reactions

   overview

   Examined as a single unit within Chemical Equilibria — no further topic split in the official outline.

Chemical Equilibria flashcards for GATE Life Sciences

19 of 52 cards from the Chemical Equilibria deck — real questions with worked answers.

1. What are colligative properties, and what are the four classic examples?

   Colligative properties depend only on the number of solute particles (not their identity). The four are: (1) relative lowering of vapor pressure, (2) elevation of boiling point, (3) depression of freezing point, and (4) osmotic pressure.

2. Define osmotic pressure ($\pi$).

   Osmotic pressure is the minimum external pressure that must be applied to a solution to prevent the net inflow of pure solvent across a semipermeable membrane (i.e., to just stop osmosis).

3. State the van't Hoff equation for osmotic pressure of a dilute solution.

   $$\pi = C R T = \frac{n}{V} R T$$ where $C$ is molar concentration, $R$ the gas constant, $T$ absolute temperature, $n$ moles of solute, and $V$ the solution volume.

4. How is the molar mass of a solute determined from osmotic pressure?

   From $\pi V = \frac{w}{M} R T$, rearranged to $$M = \frac{w R T}{\pi V}$$ where $w$ is the mass of solute dissolved in volume $V$.

5. What does it mean for two solutions to be isotonic?

   Isotonic solutions have equal osmotic pressure at the same temperature ($\pi_1 = \pi_2$), hence equal molar concentration of particles, so there is no net flow of solvent between them across a semipermeable membrane.

6. Distinguish hypertonic and hypotonic solutions relative to a cell.

   A hypertonic solution has higher osmotic pressure (more concentrated) than the cell, causing water to leave the cell (crenation/plasmolysis). A hypotonic solution has lower osmotic pressure, causing water to enter the cell (swelling/haemolysis).

7. What is reverse osmosis and one major application?

   Reverse osmosis is the forced flow of solvent from a concentrated solution to pure solvent by applying a pressure greater than the osmotic pressure across a semipermeable membrane. Its major application is desalination of seawater to obtain potable water.

8. Why are colligative properties measured via osmotic pressure preferred for macromolecules like proteins?

   Osmotic pressure has a measurably large magnitude even at very low molar concentrations and is measured near room temperature (avoiding decomposition), making it ideal for determining molar masses of polymers and proteins.

9. What is the van't Hoff factor $i$, and how is it defined?

   The van't Hoff factor accounts for association or dissociation of solute. $$i = \frac{\text{observed colligative property}}{\text{calculated (normal) colligative property}} = \frac{\text{actual number of particles}}{\text{number of formula units dissolved}}$$

10. What are the values of $i$ for a non-electrolyte, for $\ce{NaCl}$, and for $\ce{K4[Fe(CN)6]}$ (complete dissociation)?

    Non-electrolyte: $i = 1$. $\ce{NaCl -> Na+ + Cl-}$: $i = 2$. $\ce{K4[Fe(CN)6] -> 4K+ + [Fe(CN)6]^{4-}}$: $i = 5$.

11. How does the van't Hoff factor modify the osmotic pressure equation for electrolytes?

    $$\pi = i\,C R T$$ The factor $i$ multiplies the concentration to account for the increased number of particles from dissociation (or the decrease from association).

12. Relate the van't Hoff factor $i$ to the degree of dissociation $\alpha$ for a solute giving $n$ ions.

    $$i = 1 + (n-1)\alpha \quad\Rightarrow\quad \alpha = \frac{i-1}{n-1}$$

13. Relate the van't Hoff factor $i$ to the degree of association $\alpha$ when $n$ molecules associate.

    $$i = 1 + \left(\frac{1}{n} - 1\right)\alpha \quad\Rightarrow\quad \alpha = \frac{1-i}{1 - \frac{1}{n}}$$ For association, $i < 1$ (e.g., benzoic acid dimerizing in benzene, $i \approx 0.5$).

14. Define the elevation of boiling point.

    Elevation of boiling point is the increase in the boiling point of a solvent when a non-volatile solute is dissolved in it: $\Delta T_b = T_b(\text{solution}) - T_b^{\circ}(\text{solvent})$, arising because the solute lowers the vapor pressure.

15. Give the formula for boiling point elevation in terms of molality.

    $$\Delta T_b = i\,K_b\,m$$ where $K_b$ is the ebullioscopic (molal boiling point elevation) constant, $m$ the molality, and $i$ the van't Hoff factor.

16. What is the ebullioscopic constant $K_b$, and what are its units?

    $K_b$ is the molal elevation constant: the boiling point elevation produced by a $1\ \text{molal}$ ideal solution. Its units are $\text{K}\cdot\text{kg}\cdot\text{mol}^{-1}$ (or $^\circ\text{C}/m$).

17. Express $K_b$ in terms of solvent properties (thermodynamic relation).

    $$K_b = \frac{R\,M_1\,T_b^{2}}{1000\,\Delta H_{vap}}$$ where $M_1$ is the solvent molar mass, $T_b$ its boiling point (K), and $\Delta H_{vap}$ its molar enthalpy of vaporization.

18. How is molar mass of a solute found from boiling point elevation data?

    $$M_2 = \frac{1000\,K_b\,w_2}{\Delta T_b\,w_1}$$ where $w_2$ is the solute mass, $w_1$ the solvent mass in grams, and $\Delta T_b$ the observed elevation.

19. Why does a non-volatile solute raise the boiling point of a solvent (molecular explanation)?

    The solute lowers the solvent's vapor pressure (fewer solvent molecules at the surface). The solution must therefore be heated to a higher temperature for its vapor pressure to reach atmospheric pressure, so it boils higher.

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