Short Q&A for Solutions (Class 12 NCERT) Revision Notes

 

Short Q&A for Short Q&A for Solutions (Class 12 NCERT)

Part 1: Basic Concepts and Concentration Terms

Q. No.	Question	Answer
1	Define a Solution.	A homogeneous mixture of two or more chemically non-reacting substances.
2	What is the major component of a solution called?	The Solvent.
3	What is the minor component of a solution called?	The Solute.
4	Define Mass Percentage (%w/w).	Mass of solute/Mass of solution×100.
5	Define Volume Percentage (%v/v).	Volume of solute/Volume of solution×100.
6	Define Mass by Volume Percentage (%w/v).	Mass of solute/Volume of solution×100.
7	Define Molarity (M).	Moles of solute per liter of solution (mol L−1).
8	Define Molality (m).	Moles of solute per kilogram of solvent (mol kg−1).
9	Which concentration term is temperature-independent: Molarity or Molality?	Molality (since mass does not change with temperature).
10	Define Mole Fraction (χ).	Ratio of the moles of one component to the total moles of all components.
11	What is the sum of the mole fractions of all components in a solution?	Unity (1).
12	Define Parts per Million (ppm).	Mass of component/Mass of solution×106.
13	When is the ppm unit typically used?	When the solute is present in a trace amount (very low concentration).
14	What is the concentration of a 1 M NaOH solution in mol L−1?	1 mol L−1 (Molarity definition).
15	What is the mole fraction of the solvent in a solution where χsolute​=0.2?	0.8 (1−0.2).
16	Write the formula for Molarity in terms of density.	M=Molar Mass1000×d×Mass %​.

Part 2: Solubility, Henry's Law, and Raoult's Law

Q. No.	Question	Answer
17	Define Solubility.	The maximum amount of solute that can dissolve in a specified amount of solvent at a given temperature.
18	What is the principle that governs the solubility of one substance in another?	"Like dissolves like" (polar in polar, non-polar in non-polar).
19	How does the solubility of most solids in liquids change with increasing temperature?	Increases (endothermic dissolution).
20	How does the solubility of gases in liquids change with increasing temperature?	Decreases (exothermic dissolution).
21	State Henry's Law.	The partial pressure of the gas (P) in the vapour phase is proportional to the mole fraction (χ) of the gas in the solution (P=KH​⋅χ).
22	What is the significance of the Henry's Law constant (KH​)?	Higher KH​ value indicates lower solubility of the gas.
23	How does increasing pressure affect the solubility of a gas in a liquid?	Increases the solubility (as per Henry's Law).
24	Give a real-life application of Henry's Law.	Carbonated soft drinks (sealing under high pressure) or scuba diving (N2​ solubility in blood).
25	State Raoult's Law for a volatile solute/solvent.	The partial vapor pressure of each component is directly proportional to its mole fraction in the solution (PA​=PA∘​⋅χA​).
26	State Raoult's Law for a non-volatile solute.	The relative lowering of vapour pressure is equal to the mole fraction of the solute.
27	What is the formula for the Relative Lowering of Vapour Pressure (RLVP)?	P∘ΔP​=P∘P∘−Ps​​=χ2​ (χ2​ is mole fraction of solute).
28	What is an Ideal Solution?	A solution that obeys Raoult's Law at all temperatures and concentrations.
29	What are the enthalpy and volume changes for the formation of an Ideal Solution?	ΔHmix​=0 and ΔVmix​=0.
30	Give an example of an approximately ideal solution.	n-Hexane and n-Heptane or Benzene and Toluene.
31	What causes a Positive Deviation from Raoult's Law?	A-B attraction is weaker than A-A and B-B attractions.
32	What is observed regarding the volume and vapor pressure in a Positive Deviation?	ΔVmix​>0 and Vapour Pressure is higher than predicted.
33	Give an example of a solution showing Positive Deviation.	Ethanol and Acetone or CS2​ and Acetone.
34	What causes a Negative Deviation from Raoult's Law?	A-B attraction is stronger than A-A and B-B attractions.
35	What is observed regarding the enthalpy and vapor pressure in a Negative Deviation?	ΔHmix​<0 (exothermic) and Vapour Pressure is lower than predicted.
36	Give an example of a solution showing Negative Deviation.	Phenol and Aniline or Chloroform and Acetone.
37	What is an Azeotrope?	A binary mixture that boils at a constant temperature and distils over without a change in composition.
38	What type of azeotrope is formed by solutions showing Positive Deviation?	Minimum boiling azeotrope.
39	What type of azeotrope is formed by solutions showing Negative Deviation?	Maximum boiling azeotrope.

Part 3: Colligative Properties (General)

Q. No.	Question	Answer
40	Define Colligative Properties.	Properties of a solution that depend only on the number of solute particles (moles), irrespective of their nature.
41	Name the four colligative properties.	RLVP, EBP, DFP, and Osmotic Pressure.
42	What does RLVP stand for?	Relative Lowering of Vapour Pressure.
43	What does EBP stand for?	Elevation in Boiling Point (ΔTb​).
44	What does DFP stand for?	Depression in Freezing Point (ΔTf​).
45	How is ΔTb​ related to molality?	ΔTb​=Kb​⋅m (Kb​ is Ebullioscopic Constant).
46	How is ΔTf​ related to molality?	ΔTf​=Kf​⋅m (Kf​ is Cryoscopic Constant).
47	What is the unit of the Ebullioscopic Constant (Kb​)?	K kg mol−1.
48	What is the unit of the Cryoscopic Constant (Kf​)?	K kg mol−1.
49	What property of the solvent determines the values of Kb​ and Kf​?	Nature of the solvent (e.g., Water has fixed Kb​ and Kf​).
50	Define Osmosis.	The spontaneous flow of solvent molecules through a semipermeable membrane (SPM) into the solution (or from lower to higher concentration).
51	Define Osmotic Pressure (π).	The excess pressure that must be applied to a solution to prevent the flow of solvent molecules into the solution through an SPM.
52	Write the formula for Osmotic Pressure (van't Hoff equation).	π=CRT (C is Molar concentration).
53	Which colligative property is preferred for determining the molar mass of polymers and biomolecules?	Osmotic Pressure (due to large pressure change and measurement at room temperature).
54	What is the phenomenon when a cell placed in a hypotonic solution swells?	Endosmosis.
55	What is the phenomenon when a cell placed in a hypertonic solution shrinks?	Exosmosis (Plasmolysis).
56	Define Hypertonic Solution.	A solution having higher osmotic pressure than the reference solution.
57	Define Hypotonic Solution.	A solution having lower osmotic pressure than the reference solution.
58	Define Isotonic Solution.	Solutions having the same osmotic pressure (no osmosis occurs between them).
59	What is the required concentration of saline solution for intravenous injection (Isotonic with blood)?	0.9% (w/v) NaCl solution.
60	Define Reverse Osmosis (RO).	Osmosis in reverse direction when an external pressure greater than the osmotic pressure is applied to the solution side.
61	What is the primary application of Reverse Osmosis?	Desalination of seawater.

Part 4: Abnormal Molar Masses and van't Hoff Factor (i)

Q. No.	Question	Answer
62	What leads to Abnormal Molar Masses in colligative property measurements?	Association or Dissociation of solute particles in the solution.
63	Define the van't Hoff Factor (i).	Ratio of the actual number of particles to the expected number of particles after dissolution.
64	Write the formula for i in terms of colligative property.	i=Calculated (Normal) Colligative PropertyObserved Colligative Property​.
65	What is the value of i for a solute that undergoes Association?	i<1 (Observed particles are fewer than expected).
66	What is the value of i for a solute that undergoes Dissociation?	i>1 (Observed particles are more than expected).
67	What is the value of i for a non-electrolyte (like glucose or urea)?	i=1 (no dissociation/association).
68	What is the expected value of i for NaCl?	2 (dissociates into Na+ and Cl−).
69	What is the expected value of i for K2​SO4​?	3 (dissociates into 2K+ and SO42−​).
70	What is the expected value of i for Al2​(SO4​)3​?	5 (dissociates into 2Al3+ and 3SO42−​).
71	How is the observed molar mass (Mobs​) related to the normal molar mass (Mcalc​) and i?	Mobs​=iMcalc​​.
72	What is the value of i when acetic acid (CH3​COOH) dimerizes in benzene?	i≈0.5 (two molecules become one).
73	Write the relationship between i and the degree of dissociation (α).	i=1+α(n−1) (n is the number of ions produced).
74	Write the relationship between i and the degree of association (α).	i=1+α(1/n−1) (n is the number of molecules that associate).
75	How do we correct the colligative property equations for electrolytes?	By multiplying the right side of the equation by the van't Hoff Factor (i).

Part 5: Graphical and Conceptual

Q. No.	Question	Answer
76	Draw a plot of Vapour Pressure vs Temperature for pure solvent and solution. Which curve lies lower?	The solution curve (due to lowering of vapour pressure).
77	How is the boiling point elevation defined graphically?	The difference between the T at which the solution curve intersects 1 atm and the T at which the solvent curve intersects 1 atm.
78	How is the freezing point depression defined graphically?	The difference between the T at which the solid solvent curve intersects the pure solvent curve and the T at which it intersects the solution curve.
79	What is the name of the membrane used in the osmosis experiment?	Semipermeable Membrane (SPM).
80	What is the key difference between an SPM and a normal filter paper?	SPM allows only solvent molecules to pass, while filter paper allows both.
81	Why is the boiling point of a solution higher than that of the pure solvent?	The vapour pressure is lower and requires a higher temperature to equal the atmospheric pressure.
82	Why is the freezing point of a solution lower than that of the pure solvent?	The vapour pressure is lower and requires a lower temperature to equal the vapour pressure of the solid solvent.
83	Does the addition of a volatile solute always lead to a lowering of vapour pressure?	No, it may lead to an increase if the solute is more volatile than the solvent.
84	What is the relationship between the osmotic pressure of two isotonic solutions?	π1​=π2​ (C1​=C2​ at same T).
85	If the atmospheric pressure is 1 bar, what is the pressure at the boiling point of the pure solvent?	1 bar.

Part 6: Numerical and Practical Concepts

104	Which component determines the vapour pressure of the solution in Raoult's Law (non-volatile solute)?	The Solvent (Ps​≈Psolvent​).
105	Does a change in external pressure affect the magnitude of osmotic pressure?	No, osmotic pressure is an intrinsic property of the solution.
106	Why are polymers prone to showing abnormal molar masses?	They tend to associate in solution, causing i<1.
107	What is the effect of adding a non-volatile solute on the chemical potential of the solvent?	It lowers the chemical potential of the solvent.
108	How does the viscosity of a liquid change with increasing temperature?	Generally decreases.
109	What happens to the partial pressure of N2​ in the lungs when we breathe at high altitude?	It decreases (leading to lower O2​ and N2​ in blood).
110	Why does CaCl2​ lower the freezing point of water more effectively than NaCl?	CaCl2​ gives 3 ions (i=3) while NaCl gives 2 ions (i=2).
111	What is the molar mass of an unknown substance if EBP is measured using a Cryoscopic Method?	It is an error; EBP method yields the molar mass, not the Cryoscopic method. (DFP is Cryoscopic).
112	What is the maximum number of decimal places allowed in the final calculated Molarity?	Depends on the least precise measurement used in the calculation (significant figures rule).

Quiz Revision Notes Downloads Class Notes Video Lectures