NEET Study Notes for Solutions: The homogeneous mixture of two or more substances that are nonreactive in nature are called solutions. The composition of these substances can be in different quantities or in different physical states. However, a binary solution consists of two substances only.

• A solution consists of solute and solvent. The substance that is present in a small quantity is called solute while the constituent that is present in a large quantity is called the solvent.
• Solution is an important topic in NEET Chemistry Syllabus, the study notes will help you in understanding the different types of solutions, colligative properties, how to determine the molecular mass using these properties.
• The sample questions provided in the article will also help you to practice questions to prepare for NEET 2022.

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NEET Study Notes for Solutions: Important Topics

Classification of Solutions

Solutions can be classified into different types based on broad characteristics. Since solutions may have different physical states, solutions can be classified on the basis of the physical state of solvent and solute

On the basis of solute dissolution in solvent, solutions can be classified as supersaturated, unsaturated, and saturated solutions.

• Supersaturated solution- A solution is said to be a saturated solution when solute in a large amount is dissolved at a specific temperature. The excess solutes crystallize fast as a result.
• Saturated solution- When a solvent cannot dissolve more solute in the solution at a specific temperature, it is called a saturated solution.
• Unsaturated solution- when a solvent can dissolve more solute in solution at a specific temperature, it is called an unsaturated solution.

Based on the quantity of solute that is dissolved in a solvent, the solution can be classified into:

• Dilute solution- when a small quantity of solute is dissolved in a solvent, it is called a dilute solution.
• Concentrate solution- When a large quantity of solute is dissolved in a solvent, it is called a concentrated solution.

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Another form of classification of solutions is based on whether the solvent is waste or other solvents are used

• Aqueous Solution- When the solvent is water, the solution is known as an aqueous solution. Example- salt solution, sugar solution, copper sulfate solution.
• Non-Aqueous solution- When solvents other than water are used, the solution is known as a non-aqueous solution.

On the basis of compositions

• Homogeneous Solution- When the properties and composition of solvents and solute is uniform, the solution is said to be homogeneous. Example- salt, sugar solution, perfume, coffee, etc.
• Heterogeneous Solution- When the properties and composition of solvents and solute is not uniform, the solution is said to be heterogeneous. Example- oil and water solution, water and chalk powder solution, etc.

On the basis of solute concentration:

• Hypotonic Solution- when the solute concentration external to the cell is less than the outer solution tends to get dispersed and bloats due to osmosis. This reaction is called Hypotonic Solution.
• Hypertonic Solution- When the solution concentration external to the cell is higher than water flows outside the cell and shrinks the cell. This is called Hypertonic Solution.
• Isotonic Solution- When the solute concentration both inside and outside the cell is uniform, the pressure normalizes causing the water to flow in any direction. This is called Isotonic Solution.

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Solubility

The ability of a solute to dissolve in a solution is called at a specific temperature is known as the solubility of the solute. The factors that affect solubility include- the temperature of the solution, nature of the solvent, nature of solute, and pressure in case of solubility of gases.

Methods of expression of concentration of solution

The concentration of solution indicates the composition of the solution. The concentration of the solution can be expressed in qualitative and quantitative terms, Qualitatively the classification of solutions eg- saturated, unsaturated, homogeneous, heterogeneous demonstrate the concentration of the solution. Quantitatively, the following methods can be used:

• Mole Fraction-
• Mass Fraction - Mass fraction of A ;

Mass fraction of B 

• Molarity- 

• Molality- 

• Parts per million (ppm) - Number of parts of component  
• Mass percentage- 

• Volume percentage- 

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Colligative Properties

The property which is determined by particle numbers rather than the nature of particles are called Colligative properties. These are

• Relative lowering in vapor pressure-When in a pure solvent, the non-volatile solute is added, the surface gets occupied by solute and solvent particles. This leads to a lower fraction of molecules that are occupied by solvent as compared to the initial phase when only solvent particles occupied the surface. The vapor pressure of the solution is thus less than that of the pure solvent.

This difference between the vapor pressure of pure solvent and solution is defined as the lowering of vapor pressure. Relative lowering in vapor pressure is 

• Elevation of Boiling Point- when the vapor pressure and atmospheric pressure are the same, it is known as the boiling point of the liquid. The boiling point of the liquid increases and vapor pressure decreases on the addition of non-volatile solute. This difference between the boiling point of pure solvent and the boiling point of the solution is called the elevation in boiling point.

Consider T⁰b boiling point of pure solvent

Tb is the boiling point of solution

Thus , the elevation of boiling point is ΔTb= T⁰b- Tb

The relationship between elevation of boiling point and molality of solute ΔTb α m

ΔTb= kb m

where kb is the mole elevation constant

when value of m is substituted

ΔTb = 1000. kb. m2/ M2 . m1

where

m2 is mass of solvent in g

m2 is mass of solvent in kg

M₁ is the molar mass of solute

• Depression in Freezing Point- The freezing point of a substance is defined as the temperature at which the vapor pressure of liquid of a substance and vapor pressure of solid in a substance becomes equal.

The difference between the freezing point of pure solvent and solution is the depression in the freezing point.

Consider T⁰f is the boiling point of pure solvent

Tf is the boiling point of the solution

Depression in freezing point can be represented by ΔTf= T⁰f - Tf

Depression in freezing point is directly related to ‘m’ molality

ΔTf = 1000. Kf . m2 / M2 . m1

where Kf is the molal depression constant

m₂ is the mass of solvent in g

m₁ is the mass of solvent in Kg

M₂ Is the molar mass of solute

• Osmotic Pressure- When solvent molecules flow from pure solvent to a solution through a semi-permeable membrane, it is called osmosis. Osmotic pressure is the application of extra pressure to restrict this flow of solvent molecules.

Osmotic pressure is represented by n

molarity is represented by c

Temperature is represented by T

Then, π∝CT

Also n= CRT, where R is the gas constant

n=(n2/ V) RT

where v is the volume of solution in liters

n₂ Is the moles of the solute

weight of solute m₂, the molar mass of solute is

Then n2 = m2/M2

n= m2RT/ VM?

Thus by knowing the value of n, m2, T, and V the molar mass of solute can be calculated.

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Raoult’s Law

Raoult’s law was formulated by Francois- Marie Raoult, a French chemist in 1887. The law is useful for the application of the solution of two volatile liquids.

As per Raoult’s Law, the partial vapor pressure of a solution’s each component is directly proportional to the component’s mole fraction”

where = vapor pressure of liquid component 1 at the same temperature

X is the mole fraction of solution components

P is the vapor pressure of solution component

Determination of molecular masses using colligative properties

Molecular mass can be determined from the colligative properties. These are:

• Boiling Point Elevation 

where K_b is the mole elevation constant

W is the weight of the solvent

w is the weight of the solute

• Depression in Freezing Point- 

Where K_f is the molar depression constant

w is the weight of solute that is non-volatile

ΔT_f = depression in freezing point

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Van’t Hoff factor

Solutes effect on colligative properties of the solution is demonstrated by Vant’s Hoff factor. Van’s Hoff factor is represented by ‘i’. The ratio of particle concentration that forms on dissolving a substance in the substance concentration by mass.

Van’s Hoff factor is also the amount to which the substance of solution associates or dissociates. For example- on dissolving a non-electrolytic substance in water, the value of Van’t Hoff factor will be 1. The value of i will equal total ions present in one formula unit of substance. When the solution is formed in water due to the presence of an ionic compound. The value of i for electrolytic solutions will be less in comparison to the estimated value. The more charged ions there are, the more deviation will take place.

What are Association and Dissociation and what are their effects?

• Association- the combining of two or more particles to form a single unit is known as an association. In association, the molar mass is greater than the predicted value of i. The value of i is less than 1. Colligative properties are also lower than the predicted value. Examples of the association are carboxylic acid on dissolving in benzene gives rise to its dimerization.

• Dissociation- When particles are split to form multiple entities, it is known as dissociation. Moar mass value is greater than normal value. Value of i is more than 1. Colligative properties are generally of higher value. Examples of dissociation are- on dissolving sodium chloride in water, the molecules of sodium and chlorine separate.

NEET Sample MCQs on Solution

Question: What are the solution of mercury and other metals known as?

1. Amalgam
2. Saturated Solution
3. Unsaturated Solution
4. Supersaturated solution

Answer: Amalgam

Question: Which amongst the following is a homogeneous mixture?

1. Sewage water
2. Buttermilk in water
3. Starch solution
4. Sugar in water

Answer: Sugar in water

Question: Which solution gives rise to allow?

1. Emulsion
2. Solid Solution
3. Colloidal Solution
4. Heterogeneous mixture

Answer: Solid Solution

Question: What happens when salt is added to water?

1. Freezing point increases
2. Boiling point increases
3. Boiling point decreases
4. No change in boiling point

Answer: Boiling point increases

Question: Which properties are demonstrated by colloidal sols?

• Van der Waals forces
• Tyndall Effect
• Maxwell distribution
• Brownian motion

1. A,b and c
2. a and b
3. a and c
4. b and d

Answer: a and b

Question: the concentration of solution does depend on temperature, what is this phenomenon called?

1. Molar fraction
2. Normality
3. Molarity
4. Molality

Answer: Molality