Question
What is Osmosis? What is Osmotic Pressure? Derive it's formula.
✓
Answer
$\rightarrow$ If semi permeable membrane is placed between the solvent and solution as shown fig. the solvent molecules will flow through the membrane from pure solvent to the solution. This process of flow of the solvent is called osmosis.
$\rightarrow$ The flow will continue till the equilibrium is attained
$\rightarrow$ The flow of the solvent from its side to solution side across a semipermeable membrane can be stopped if some extra pressure is applied on the solution. This pressure that just stops the flow of solvent is called osmotic pressure of the solution.
$\rightarrow$ The osmotic pressure of a solution is the excess pressure that must be applied to a solution to prevent osmosis,
$\rightarrow$ Osmotic pressure is a colligative property as it depends on the number of solute molecules and not on their identity.
$\rightarrow$ osmotic pressure is proportional to the molarity, $C$ of the solution at a given temperature $T.$
$\pi=\text { CRT }$
Where, $\pi=$ Osmotic pressure
$R =$gas constant
$ \therefore \pi =\frac{n_2 R T}{V} \quad\left(\because C=\frac{n_2}{V}\right)$
$\pi =\frac{W_2 R T}{M_2 V}$
$ W _2=$ Wt . of Solute
$M _2=$ Molar mass of Solute
$V =$Volume of Solution$(L)$
$T =$Temperature
$\rightarrow$ The flow will continue till the equilibrium is attained
$\rightarrow$ The flow of the solvent from its side to solution side across a semipermeable membrane can be stopped if some extra pressure is applied on the solution. This pressure that just stops the flow of solvent is called osmotic pressure of the solution.
$\rightarrow$ The osmotic pressure of a solution is the excess pressure that must be applied to a solution to prevent osmosis,
$\rightarrow$ Osmotic pressure is a colligative property as it depends on the number of solute molecules and not on their identity.
$\rightarrow$ osmotic pressure is proportional to the molarity, $C$ of the solution at a given temperature $T.$
$\pi=\text { CRT }$
Where, $\pi=$ Osmotic pressure
$R =$gas constant
$ \therefore \pi =\frac{n_2 R T}{V} \quad\left(\because C=\frac{n_2}{V}\right)$
$\pi =\frac{W_2 R T}{M_2 V}$
$ W _2=$ Wt . of Solute
$M _2=$ Molar mass of Solute
$V =$Volume of Solution$(L)$
$T =$Temperature
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Raoult's law for volatile liquids states that the partial vapour pressure of each component in the solution is directly proportional to its mole fraction, whereas for a non $-$ volatile solute, it states that the vapour pressure of a solution of a non $-$ volatile solute is equal to the vapour pressure of the pure solvent at that temperature multiplied by its mole fraction. Two liquids $A$ and $B$ are mixed with each other to form a solution, the vapour phase consists of both components of the solution. Once the components in the solution have reached equilibrium, the total vapour pressure of the solution can be determined by combining Raoult's law with Dalton's law of partial pressures. If a non $-$ volatile solute $B$ is dissolved into a solvent $A$ to form a solution, the vapour pressure of the solution will be lower than that of the pure solvent. The solutions which obey Raoult's law over the entire range of concentration are ideal solutions, whereas the solutions for which vapour pressure is either higher or lowerthan that predicted by Raoult's law are called non $-$ ideal solutions. Non $-$ ideal solutions are identified by determining the strength of the intermolecular forces between the different molecules in that particular solution.They can either show positive or negative deviation from Raoult's law depending on whether the $A - B$ interactions in solution are stronger or weaker than $A - A$ and $B - B$ interactions.
$i. 20 \ mL$ of a liquid $A$ was mixed with $20 \ mL$ of liquid $B$. The volume of resulting solution was found to be less than $40 \ mL$. What do you conclude from the above data?
$ii$. Which of the following show positive deviation from Raoult's law? Carbon disulphide and Acetone; Phenol and Aniline; Ethanol and Acetone.
$iii$. The vapour pressure of a solution of glucose in water is $750\ mm\ Hg$ at $100^\circ C$. Calculate the mole fraction of solute.
$($Vapour pressure of water at $373 K = 760 \ mm\ Hg)$
OR
$iii$. The boiling point of solution increases when $1$ mol of $\ce{NaCl}$ is added to $1$ litre of water while addition of $1$ mol of methanol to one litre of water decreases its boiling point. Explain the above observations.
→Raoult's law for volatile liquids states that the partial vapour pressure of each component in the solution is directly proportional to its mole fraction, whereas for a non $-$ volatile solute, it states that the vapour pressure of a solution of a non $-$ volatile solute is equal to the vapour pressure of the pure solvent at that temperature multiplied by its mole fraction. Two liquids $A$ and $B$ are mixed with each other to form a solution, the vapour phase consists of both components of the solution. Once the components in the solution have reached equilibrium, the total vapour pressure of the solution can be determined by combining Raoult's law with Dalton's law of partial pressures. If a non $-$ volatile solute $B$ is dissolved into a solvent $A$ to form a solution, the vapour pressure of the solution will be lower than that of the pure solvent. The solutions which obey Raoult's law over the entire range of concentration are ideal solutions, whereas the solutions for which vapour pressure is either higher or lowerthan that predicted by Raoult's law are called non $-$ ideal solutions. Non $-$ ideal solutions are identified by determining the strength of the intermolecular forces between the different molecules in that particular solution.They can either show positive or negative deviation from Raoult's law depending on whether the $A - B$ interactions in solution are stronger or weaker than $A - A$ and $B - B$ interactions.
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$iii$. The vapour pressure of a solution of glucose in water is $750\ mm\ Hg$ at $100^\circ C$. Calculate the mole fraction of solute.
$($Vapour pressure of water at $373 K = 760 \ mm\ Hg)$
OR
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