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SOLUTIONS in 2 Hours || BEST for Class 12th Boards || Pure English

PW English Medium・102 minutes read

Physics Walla is a platform for one-shot revision on solutions, focusing on the conceptual part in the session and numerical aspects in the next session. The text covers the definition of solutions, classification, concentration terms, Raoult's Law, Dalton's Law, Henry's Law, vapor pressure, colligative properties, osmotic pressure, and reverse osmosis.

Insights

Solutions are composed of solutes dissolved in solvents, with various concentration terms used to quantify the amount of solute present in the solvent.
Raoult's Law and Dalton's Law provide insights into how vapor pressures change in solutions, with the total vapor pressure being the sum of the partial pressures of each component.
Lowering of vapor pressure, a colligative property, depends on the number of moles of solute and solvent present, affecting the overall vapor pressure in a solution.
Ideal solutions adhere to Raoult's Law, while non-ideal solutions exhibit positive or negative deviations due to interactions post-mixing, impacting the total pressure observed.

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Recent questions

What is a solution?
A homogeneous mixture with solute and solvent.

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Summary

00:00

"Understanding Solutions: Concepts and Concentrations"

Physics Walla platform for one-shot revision on solutions
Focus on conceptual part in this session, numerical part in next
Definition of solution: homogeneous mixture with solute and solvent
Solutions can have one solvent and one or more solutes
Classification of solutions: binary, ternary, quaternary
Default assumption for unspecific solutions is binary
Concentration terms express amount of solute in solvent
Salute is reactive part, solvent provides medium for reaction
Amount of solute in solution represented by concentration
Molarity: moles of solute per liter of solution, formula: moles of solute/volume of solution in liters

17:53

Understanding Solution Concentration Calculations in Chemistry

A 3 molal NaOH solution contains 3 moles of NaOH in 1 kg of solvent, with water typically being the solvent in aqueous solutions.
The term "aqueous" signifies water as the solvent in a solution, with the solute being specified by the compound mentioned.
Mass by volume percentage involves calculating the mass of solute in 100 ml of solution, with mass in grams and volume in milliliters being crucial.
The formula for mass by volume percentage is mass of solute in grams divided by volume of solution in milliliters, multiplied by 100.
Decoding expressions like "10 mass by volume percentage of aqueous NaOH solution" reveals the grams of solute present in 100 ml of solution.
Mass by mass percentage is determined by dividing the mass of solute in grams by the mass of solution in grams, then multiplying by 100.
Expressions like "10% mass by mass aqueous NaOH solution" indicate the grams of NaOH present in 100 grams of solution.
Calculating molality involves finding moles of solute divided by mass of solvent in kgs, while molarity requires moles of solute divided by volume of solution in liters.
Volume by volume percentage calculates the milliliters of solute in 100 ml of solution, with the formula being volume of solute in ml divided by volume of solution in ml, multiplied by 100.
Mole fraction, represented by x or chi, is the fraction of moles of a component in a solution, with the sum of all mole fractions always equating to one.

36:08

Understanding Parts per Million and Vapor Pressure

Parts per million (ppm) is a concentration term used widely nowadays, equivalent to a percentage.
In ppm, the calculation involves determining the grams of solute in 10^6 grams of solution.
The formula for ppm is the mass of solute divided by the mass of solution in grams, multiplied by 10^6.
Decoding ppm values involves understanding the grams of solute in 10^6 grams of solution.
Vapor pressure is the pressure exerted by vapor in equilibrium with a liquid in a closed container.
Vapor pressure depends solely on temperature and the liquid's nature, remaining constant at a specific temperature.
Vapor pressure is not influenced by the container's volume or the liquid's amount, only by temperature and liquid nature.
Raoult's Law explains vapor pressure in solutions, where the total vapor pressure is the sum of the partial pressures of each component.
Mixing volatile components in a container alters their individual vapor pressures due to hindrance from each other.
The total vapor pressure in a mixed solution is the sum of the partial pressures of each component present.

53:13

Calculating Vapor Pressures in Solutions

Raoult's law explains how to calculate vapor pressures of solute and solvent in a solution.
The partial pressure of a component is proportional to its mole fraction in the solution.
If a component has more moles, its partial pressure will be higher.
Raoult's law states that the partial pressure of a component is directly proportional to its mole fraction.
The total pressure of a solution is the sum of the partial pressures of its components.
Dalton's law relates the partial pressure of a component in the vapor phase to its mole fraction and the total pressure.
Equating the partial pressures of components gives expressions for calculating total pressure in terms of mole fractions.
Raoult's law and Dalton's law provide equations for calculating partial pressures in mixtures.
When one component is non-volatile, its partial pressure is zero, affecting the total vapor pressure.
Adding a non-volatile solute decreases the total vapor pressure due to hindrance in vapor formation by the non-volatile component.

01:10:44

Vapor Pressure Lowering in Solutions Explained

Lowering of vapor pressure is calculated as the difference between the initial pressure (p naught) and the final pressure (p dash).
The expression for lowering of vapor pressure can be simplified to p naught times the mole fraction of the non-volatile solute (x b).
The more non-volatile solute present, the greater the lowering of vapor pressure, as it is directly proportional to the mole fraction of the solute.
Lowering of vapor pressure depends on the nature of the solvent and the amount of non-volatile solute, not on the nature of the solute.
Delta p, the lowering of vapor pressure, is a qualitative, colligative property dependent on the number of moles of the solute and solvent.
Relative lowering of vapor pressure (delta p / p naught) is a colligative property with respect to both the solute and solvent, as it depends solely on the moles of solute and solvent.
Henry's Law states that the pressure of a gas in a liquid is directly proportional to its solubility, with pressure being proportional to the mole fraction of the solute.
Henry's Law constant (k h) does not depend on pressure but on temperature, the nature of the gas, and the nature of the liquid.
A gas with a higher van der Waals constant (a) is more easily liquefiable and therefore more soluble in water, leading to increased solubility.
The greater the van der Waals constant (a) value, the more soluble the gas, as solubility is directly related to the mole fraction of the solute.

01:27:50

Gas Behavior and Ideal Solutions Explained

A gas with a higher a value in the van der Waals constant is more liquefiable and soluble, with a lower Henry's Law constant.
An increase in temperature leads to an increase in the Henry's Law constant.
Ideal solutions follow Raoult's Law, with non-ideal solutions deviating from it.
Ideal solutions have equal interactions between solute-solute, solvent-solvent, and solute-solvent bonds, resulting in zero enthalpy mixing and volume change.
The entropy factor measures randomness, with higher entropy indicating more randomness.
Deviation from Raoult's Law can be positive or negative, depending on the strength of interactions after mixing.
Positive deviation results in higher total pressure than calculated for an ideal solution, due to weaker interactions post-mixing.
Negative deviation leads to lower total pressure than expected for an ideal solution, caused by stronger interactions post-mixing.
Positive deviation entails positive enthalpy mixing, positive volume change, and positive entropy.
Examples of ideal solutions include benzene-toluene, n-hexane-n-heptane, and dimethyl ether-dimethyl ether.

01:45:28

Intermolecular Forces and Colligative Properties Explained

Delta H mixing is negative when solute-solute and solvent-solvent bonds are broken, with a stronger force of interactions leading to a decrease in volume.
Molecular attractions increase after mixing, causing molecules to draw closer and volume to decrease, resulting in a positive delta S mixing.
Negative deviation occurs when a volatile solute or stronger electrolyte is dissolved in water, leading to a decrease in total pressure compared to ideal solutions.
Drawing a graph illustrates the negative deviation, showcasing how the total pressure is less than ideal solutions.
Elevation of boiling point is discussed, emphasizing that it depends on the amount of non-volatile solute added, with delta T b being directly proportional to molality.
Boiling point is reached when the vapor pressure equals atmospheric pressure, with the boiling point of a solution being higher than that of the pure solvent.
Depression in freezing point occurs when a non-volatile solute is added, leading to a decrease in freezing point, with delta T f being directly proportional to molality.
Osmotic pressure is explained through the movement of solvent from high concentration to low concentration through a semi-permeable membrane, with the solvent exerting pressure as it moves.

02:03:20

Understanding Osmotic Pressure and Reverse Osmosis

Osmotic pressure is defined as the pressure exerted when a pure liquid moves to the solution side, and it can be stopped by applying pressure equal to the osmotic pressure.
Osmosis occurs through a semi-permeable membrane, with solvent molecules moving from the pure solvent side to the solution side, resulting in osmotic pressure on the solution side.
Reverse osmosis happens when pressure applied on the solution side exceeds the osmotic pressure, causing solvent to flow back from the solution side to the pure solvent side, purifying water in RO systems.

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