Chapter : Solutions

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Solutions Chapter: Quick Revision Q&A

Basic Concepts and Concentration Terms

1. Q: Define a solution. A: A homogeneous mixture of two or more chemically non-reacting substances whose composition can be varied within certain limits.

2. Q: What are the two main components of a binary solution? A: Solute (lesser amount) and Solvent (greater amount).

3. Q: Define Mass Percentage (% w/w). A: Mass of the component in the solution divided by the total mass of the solution, multiplied by 100.

4. Q: Define Molarity (M). A: The number of moles of solute dissolved per liter of solution. ($\text{M}=\frac{\text{Moles of solute}}{\text{Volume of solution in L}}$).

5. Q: Define Molality (m). A: The number of moles of solute dissolved per kilogram of solvent. ($\text{m}=\frac{\text{Moles of solute}}{\text{Mass of solvent in kg}}$).

6. Q: Which concentration term is temperature-independent? A: Molality ($\text{m}$) and Mole Fraction ($\chi$), as they involve mass/moles, not volume.

7. Q: Define Mole Fraction (χ). A: The ratio of the number of moles of one component to the total number of moles of all components in the solution.

8. Q: How is the concentration of a pollutant in water often expressed? A: In Parts Per Million ($\text{ppm}$), as the solute is in trace amounts.

9. Q: What is the relationship between Normality (N) and Molarity (M)? A: $\text{N}=\text{M}\times \text{Valency factor}$ (or n-factor).

10. Q: What happens to the molarity of a solution if it is diluted? A: Molarity decreases because the volume of the solution increases, while the moles of solute remain constant (${\text{M}}_1{\text{V}}_1={\text{M}}_2{\text{V}}_2$).

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Solubility and Henry's Law

11. Q: Define solubility. A: The maximum amount of a solute that can be dissolved in a specified amount of solvent at a specified temperature.

12. Q: State the effect of temperature on the solubility of a gas in a liquid. A: Solubility of gases generally decreases with an increase in temperature (dissolution is often an exothermic process).

13. Q: State the effect of pressure on the solubility of a gas in a liquid. A: Solubility of gases increases with an increase in pressure.

14. Q: State Henry's Law. A: The partial pressure of a gas in the vapor phase (p) is proportional to the mole fraction of the gas (χ) in the solution. ($\text{p}={\text{K}}_{\text{H}}\chi$).

15. Q: How is the Henry's Law constant (${\text{K}}_{\text{H}}$) related to the solubility of a gas? A: Higher the value of KH​, the lower is the solubility of the gas in the liquid at the same partial pressure.

16. Q: Give a common application of Henry's Law related to soft drinks. A: Soft drinks are bottled under high pressure to increase the solubility of CO2​ gas.

17. Q: What causes the painful condition called 'bends' in deep-sea divers? A: The sudden release of dissolved nitrogen gas bubbles in the blood when the diver ascends too quickly, due to a decrease in pressure.

18. Q: Why do aquatic species feel more comfortable in cold water? A: The solubility of oxygen gas is higher in cold water than in warm water.

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Vapour Pressure and Raoult's Law

19. Q: Define Vapour Pressure. A: The pressure exerted by the vapors of a liquid in equilibrium with the liquid at a given temperature.

20. Q: State Raoult's Law for a solution of two volatile liquids. A: For a solution of volatile liquids, the partial vapour pressure of each component in the solution is directly proportional to its mole fraction in the solution (${\text{p}}_{\text{i}}={\text{p}}_{\text{i}}^{\circ }{\chi }_{\text{i}}$).

21. Q: What is an Ideal Solution? A: A solution that obeys Raoult's Law over the entire range of concentration and temperature.

22. Q: What are the two main thermodynamic conditions for an Ideal Solution? A: $\Delta {\text{H}}_{\text{mix}}=0$ (no heat change) and $\Delta {\text{V}}_{\text{mix}}=0$ (no volume change).

23. Q: Give an example of an Ideal Solution. A: Benzene and Toluene, or n-Hexane and n-Heptane.

24. Q: What characterizes a solution showing Positive Deviation from Raoult's Law? A: The vapour pressure is higher than expected (${\text{P}}_{\text{Total}}>{\text{P}}_{\text{ideal}}$), due to weaker A-B interactions than A-A and B-B interactions.

25. Q: Give an example of a solution showing Positive Deviation. A: Ethanol and Acetone, or Carbon disulfide and Acetone.

26. Q: What characterizes a solution showing Negative Deviation from Raoult's Law? A: The vapour pressure is lower than expected (${\text{P}}_{\text{Total}}<{\text{P}}_{\text{ideal}}$), due to stronger A-B interactions than A-A and B-B interactions.

27. Q: Give an example of a solution showing Negative Deviation. A: Chloroform and Acetone, or Phenol and Aniline.

28. Q: What is an Azeotrope? A: A binary mixture that has the same composition in the liquid and vapor phases and boils at a constant temperature.

29. Q: What is a Minimum Boiling Azeotrope associated with? A: Solutions showing Positive Deviation from Raoult's Law.

30. Q: What is a Maximum Boiling Azeotrope associated with? A: Solutions showing Negative Deviation from Raoult's Law.

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Colligative Properties

31. Q: Define Colligative Properties. A: Properties of a dilute solution that depend only on the number of solute particles (or concentration) and not on their identity.

32. Q: List the four main Colligative Properties. A: Relative Lowering of Vapour Pressure ($\text{RLVP}$), Elevation in Boiling Point ($\Delta {\text{T}}_{\text{b}}$), Depression in Freezing Point ($\Delta {\text{T}}_{\text{f}}$), and Osmotic Pressure ($\pi$).

33. Q: State Raoult's Law for Relative Lowering of Vapour Pressure ($\text{RLVP}$). A: $\text{RLVP}=\frac{{\text{p}}^{\circ }-\text{p}}{{\text{p}}^{\circ }}$ is equal to the mole fraction of the solute (χ2​) for very dilute solutions.

34. Q: What is the formula for Elevation in Boiling Point ($\Delta {\text{T}}_{\text{b}}$)? A: $\Delta {\text{T}}_{\text{b}}={\text{K}}_{\text{b}}\times \text{m}$, where m is molality and Kb​ is the Ebullioscopic Constant.

35. Q: What is the unit of the Molal Elevation Constant (Kb​)? A: K/m or $\text{K}\cdot \text{kg}\cdot {\text{mol}}^{-1}$.

36. Q: What is the formula for Depression in Freezing Point ($\Delta {\text{T}}_{\text{f}}$)? A: $\Delta {\text{T}}_{\text{f}}={\text{K}}_{\text{f}}\times \text{m}$, where m is molality and Kf​ is the Cryoscopic Constant.

37. Q: Define Osmosis. A: The spontaneous net flow of solvent molecules through a semi-permeable membrane from a region of lower solute concentration to a region of higher solute concentration.

38. Q: Define Osmotic Pressure ($\pi$). A: The excess pressure that must be applied to the solution side to stop the flow of solvent into the solution through a semi-permeable membrane.

39. Q: What is the formula for Osmotic Pressure ($\pi$)? A: $\pi =\text{MRT}$ (like the Ideal Gas Law), where M is molarity, R is the gas constant, and T is temperature in Kelvin.

40. Q: What are Isotonic Solutions? A: Solutions having the same osmotic pressure at a given temperature (${\pi }_1={\pi }_2$).

41. Q: What is a cell placed in a Hypertonic solution? A: It will undergo crenation (shrinking) as water flows out of the cell.

42. Q: What is a cell placed in a Hypotonic solution? A: It will undergo haemolysis (swelling and bursting) as water flows into the cell.

43. Q: How can reverse osmosis be achieved, and what is its main application? A: By applying an external pressure greater than the osmotic pressure on the solution side. Main application is desalination of seawater.

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Abnormal Molar Masses and Van't Hoff Factor

44. Q: What is the term for the molar mass calculated from a colligative property that is different from the theoretical value? A: Abnormal Molar Mass.

45. Q: What is the cause of Abnormal Molar Mass? A: Association (solute particles join) or Dissociation (solute particles break apart) in the solution.

46. Q: Define the Van't Hoff Factor ($\text{i}$). A: $\text{i}=\frac{\text{Observed Colligative Property}}{\text{Calculated Colligative Property}}$ or $\text{i}=\frac{\text{Total moles of particles after association/dissociation}}{\text{Moles of particles before association/dissociation}}$.

47. Q: How does association of solute particles affect the Van't Hoff factor (i) and the observed molar mass? A: $\text{i}<1$, and the observed molar mass is higher than the theoretical value.

48. Q: How does dissociation of solute particles affect the Van't Hoff factor (i) and the observed molar mass? A: $\text{i}>1$, and the observed molar mass is lower than the theoretical value.

49. Q: What is the Van't Hoff factor (i) for a solution of a non-electrolyte like glucose? A: $\text{i}=1$, as it does not associate or dissociate.

50. Q: Write the modified equation for Depression in Freezing Point ($\Delta {\text{T}}_{\text{f}}$) including the Van't Hoff factor. A: $\Delta {\text{T}}_{\text{f}}=\text{i}\times {\text{K}}_{\text{f}}\times \text{m}$.