NCERT solutions for class 12 chemistry chapter 2 Solutions- In our daily life we come across various mixtures like soft drinks, syrups and air. All of them are mixtures of two or more pure substances like air is a mixture of mainly nitrogen and oxygen etc. Also, you know about various types of mixtures or solutions like gaseous solutions, liquid solutions and solid solutions. NCERT solutions for class 12 chemistry chapter 2 Solutions mainly discuss questions based on liquid solutions and their properties. The solutions of NCERT class 12 chemistry chapter 2 Solutions also cover other questions based on important concepts like types of solutions, Raoult's law and Henry's law, the concentration of solutions in different units, solubility, vapour pressure of liquid solutions, ideal and non-ideal solutions, colligative properties, determination of molar mass and abnormal molar masses. These topics of this chapter are not only important for the class 12 CBSE Board exam but also for the various competitive exams like JEE Mains, NEET, BITSAT, VITEEE, etc. In CBSE NCERT solutions for class 12 chemistry chapter 2 Solutions, there are direct answers to the 41 questions which are there in the chapter exercise. To develop a grip on the topic, NCERT solutions for class 12 chemistry chapter 2 Solutions are prepared by chemistry experts in a very comprehensive manner. The students will be able to find step-by-step solutions which will eventually help you to write good answers and get good marks in the CBSE exam. The NCERT solutions which are provided here are free of cost and are easily accessible and if you wish to check other classes solutions, you can just click on the above link.
What are the solutions? - The solutions are mixtures of two or more than two components and solutions are classified as solids, liquids, and gaseous solution. The concentration of the solution is expressed in terms of molarity, molality, mole fraction and in percentages.
Topics and Sub-topics of NCERT Class 12 Chemistry Chapter 2 Solutions-
2.1Types of Solutions
2.2 Expressing Concentration of Solutions
2.4 Vapour Pressure of Liquid Solutions
2.5 Ideal and Non-ideal Solutions
2.6 Colligative Properties and Determination of Molar Mass
2.7 Abnormal Molar Masses
Find NCERT solutions for class 12 chemistry chapter 2 Solutions below:
Solutions to In-Text Questions Exercise 2.1 to 2.12
We know that solute and solvent forms solution.
So mass percentage of benzene (solute) :-
Similarly mass percentage of CCl4 :-
For calculating mole fraction, we need moles of both the compounds.
It is given that benzene is in the solution by mass.
So if we consider 100g of solution then 30g is benzene and 70g is CCl4.
Similarly moles of benzene :
So mole fraction of benzene is given :
of in of solution
For finding molarity we need the moles of solute and volume of solution.
So moles of solute :
of diluted to .
By conservation of moles we can write :
M1V1 = M2V2
Given that M1 = 0.5 M and V1 = 30 ml ; V2 = 500 ml
Let us assume that the mass of urea required be x g.
So moles of urea will be :
we get x = 37
Thus mass of urea required = 37 g.
For finding Henry's constant we need to know about the mole fraction of H2S.
Solubility of H2S in water is given to be 0.195 m .
i.e., 0.195 moles in 1 Kg of water.
At STP conditions, pressure = 1 atm or 0.987 bar
Equation is :
So we get :
We know that ,
Pressure of CO2 = 2.5 atm
We know that :
So, Pressure of CO2 = Pa
By Henry Law we get,
Taking density of soda water = 1 g/ml
We get mass of water = 500 g.
So, Moles of water :
So, moles of CO2 = 0.042 mol
Using relation of mole and given mass, we get
Mass of CO2 = 1.848 g.
Let the composition of liquid A (mole fraction) be xA.
So mole fraction of B will be xB = 1 - xA.
Using Raoult’s law ,
Putting values of ptotal and vapour pressure of pure liquids in the above equation, we get :
600 = 450.xA + 700.(1 - xA)
or 600 - 700 = 450xA - 700xA
or xA = 0.4
and xB = 0.6
Now pressure in vapour phase :
= 450(0.4) = 180 mm of Hg
= 700(0.6) = 420 mm of Hg
And mole fraction of liquid B = 0.70
Given that vapour pressure of pure water,
Moles of water :
Moles of urea :
Let the vapour pressure of water be pw.
By Raoult's law, we get :
or pw = 23.4 mm of Hg.
Relative lowering :- Hence, the vapour pressure(v.P) of water in the solution = 23.4 mm of Hg
and its relative lowering = 0.0173.
Here we will use the formula :
Elevation in temperature = 100 - 99.63 = 0.37
Kb = 0.52 ;
Putting all values in above formula, we get :
Thus 121.67 g of sucrose needs to be added.
Elevation in melting point = 1.5 degree celsius.
Here we will use the following equation :
Putting given values in the above equation :
Thus 5.08 ascorbic acid is needed for required condition.
We know that :
We are given with :-
Volume, V = 0.45 L
Thus osmotic pressure :
NCERT solutions for class 12 chemistry chapter 2 Solutions : Exercises
Solution :- A solution is a homogeneous mixture of two or more non-reacting substances. It has two components :- solute and solvent.
Types of solutions are given below :-
Solution of hydrogen in palladium is such an example in which solute is a gas and solvent is solid.
Mole fraction is defined as the ratio of number of moles of a component and total number of moles in all components.
It is defined as the number of moles of solute dissolved per kg (1000g) of solvent
It is independent of temperature.
Molarity is defined as number of moles of solute dissolved per litre(or 1000ml) of solution.
It depends on temperature because volume is dependent on temperature.
Mass percentage is defined as the percentage ratio of mass of one component to the total mass of all the components.
According to given question, in 100 g of solution 68 g is nitric acid and rest is water.
So moles of 68 g HNO3 :-
Density of solution is given to be 1.504.
So volume of 100 g solution becomes :-
Thus, molarity of nitric acid is :
According to question, mass percentage means in 100 g of solution 10 g glucose is dissolved in 90 g water.
Molar mass of glucose (C6H12O6) =
So moles of glucose are :
Mole fraction :-
Molarity :- Volume of 100 g solution :
Total amount of mixture of Na2CO3 and NaHCO3 = 1 g.
Let the amount of Na2CO3 be x g.
So the amount of NaHCO3 will be equal to (1 - x) g.
Now it is given that it is an equimolar mixture.
So, Moles of Na2CO3 = Moles of NaHCO3.
or x = 0.558 g
It is clear that for 1 mol of Na2CO3 2 mol of HCl is required, similarly for 1 mol of NaHCO3 1 mol of HCl is required.
So number of moles required of HCl = 2(0.00526) + 0.0053 = 0.01578 mol
It is given that molarity of HCl is 0.1 which means 0.1 mol of HCl in 1l of solution.
Thus required volume :
According to question we have 2 solute,
Solute 1. : of 300 g gives :
Solute 2. : of 400 g gives :
So total amount of solute = 75 + 160 = 235 g.
Thus mass percentage of solute is :
and mass percentage of water
For finding molality we need to find the moles of ethylene glycol.
Moles of ethylene glycol :
We know that :
Now for molarity :-
Total mass of solution = 200 + 222.6 = 422.6 g
Volume of solution
So molarity :-
Both alcohol and water individually have strong hydrogen bonds as their force of attraction. When we mix alcohol with water they form solution due to the formation of hydrogen bonds but they are weaker as compared to hydrogen bonds of pure water or pure alcohol.
Thus this solution shows a positive deviation from the ideal behaviour.
It is known that dissolution of gas in a liquid is an exothermic process. So, by Le Chatelier principle we know that equilibrium shifts backwards as we increase temperature in case of exothermic process. Thus gases always tend to be less soluble in liquids as the temperature is raised.
Q2.12 State Henry’s law and mention some important applications.
According to Henry's law at a constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas present above the surface of solution or liquid.
i.e., p = khx, Here kh is Henry’s law constant.
Some of its applications are as follows:-
(a) We can increase the solubility of CO2 in soft drinks, the bottle is sealed under high pressure.
(b) To avoid bends (due to blockage of capillaries) and the toxic effects of high concentrations of nitrogen in the blood, the tanks used by scuba divers are filled with air diluted with helium (11.7% helium, 56.2% nitrogen and 32.1% oxygen).
(c) The partial pressure of oxygen is less at high altitudes than that at the ground level. This leads to low concentrations of oxygen in the blood and tissues climbers. Due to low blood oxygen, climbers become weak and unable to think clearly which are symptoms of a condition known as anoxia.
Q2.14 What is meant by positive and negative deviations from Raoult's law and how is the sign of related to positive and negative deviations from Raoult's law?
Positive and negative deviation:- A non-ideal solution is defined as a solution which does not obey Raoult’s law over the entire range of concentration i.e., and . The vapour pressure of these solutions is either higher or lower than that expected by Raoult’s law. If vapour pressure is higher, the solution shows a positive deviation and if it is lower, it shows a negative deviation from Raoult’s law.
Enthalpy relation to positive and negative deviation can be understood from the following example:-
Consider a solution made up of two components - A and B. In the pure state the intermolecular force of attraction between them are A-A and B-B. But when we mix the two, we get a binary solution with molecular interaction A-B.
If A-B interaction is weak than A-A and B-B then enthalpy of reaction will be positive thus reaction will tend to move in a backward direction. Hence molecules in binary solution will have a higher tendency to escape. Thus vapour pressure increases and shows positive deviation from the ideal behaviour.
Similarly, for negative deviation, A-B interaction is stronger than that of A-A and B-B.
molar mass of the solute
In this question we will find molar mass of solute by using Raoult's law .
Let the molar mass of solute is M.
Initially we have 30 g solute and 90 g water.
Moles of water :
By Raoult's law we have :-
or ------------------------------ (i)
Now we have added 18 g of water more, so the equation becomes:
Moles of H2O :
Putting this in above equation we obtain :-
From equation (i) and (ii) we get
M = 23 u
So the molar mass of solute is 23 units.
vapour pressure of water at 298 K.
In the previous part we have calculated the value of molar mass the Raoul's law equation.
We had :-
Putting M = 23 u in the above equation we get,
Thus vapour pressure of water = 3.53 kPa.
It is given that freezing point of pure water is 273.15 K.
So, elevation of freezing point = 273.15 - 271 = 2.15 K
solution means 5 g solute in 95 g of water.
Moles of cane sugar :
We also know that -
Now we will use the above procedure for glucose.
of glucose means 5 g of gluocse in 95 g of H2O.
Moles of glucose :
Thus molality :
So, we can find the elevation in freezing point:
Thus freezing point of glucose solution is 273.15 - 4.09 = 269.06 K.
In this question we will use the formula :
Firstly for compound AB2 :-
Similarly for compound AB4 :-
If we assume atomic weight of element A to be x and of element B to be y, then we have :-
x + 2y = 110.87 ----------------- (i)
x + 4y = 196 ----------------- (ii)
Solving both the equations, we get :-
x = 25.59 ; y = 42.6
Hence atomic mass of element A is 25.59u and atomic mass of element B is 42.6u.
According to given conditions we have same solution under same temperature. So we can write :
So, if we put all the given values in above equation, we get
Hence the required concentration is 0.061 M.
n-hexane and n-octane
Since both the compounds are alkanes so their mixture has van der Waal force of attraction between compounds.
The binary mixture of these compounds has van der Waal force of attraction between them.
The given compounds will have ion-dipole interaction between them.
Methanol has -OH group and acetone has ketone group. So there will be hydrogen bonding between them.
Cyclohexane, KCl, CH3OH, CH3CN.
The order will be : Cyclohexane > CH3CN > CH3OH > KCl
In this, we have used the fact that like dissolves like.
Since cyclohexane is an alkane so its solubility will be maximum.
We know the fact that like dissolves in like.
Since phenol is had both polar and non-polar group so it is partially soluble in water.
Since toluene is a non-polar compound i.e., it doesn't have any polar group so it is insoluble in water. (because water is a polar compound)
Since the -OH group in formic acid (polar) can form H-bonds with water thus it is highly soluble in water.
Ethylene glycol is an organic compound but is polar in nature. Also, it can form H-bonds with water molecules, thus it is highly soluble in water.
Chloroform is a non-polar compound so it is insoluble in water.
Pentanol has both polar and non-polar groups so it is partially soluble in water.
We know that, Molality :
So, for moles of solute we have :
Thus, molality :
Molality of Na+ ions is 4m.
We are given,
The dissociation equation of CuS is given by :-
So, the equation becomes :-
Thus maximum molarity of solution is .
Total mass of solution = Mass of aspirin + Mass of acetonitrile = 6.5 + 450 = 456.5 g.
We know that :
Thus the mass percentage of aspirin is
We are given with molality of the solution, so we need to find the moles of Nalorphene.
Molar mass of nalorphene = 19(12) + 21(1) + 1(14) + 3(16) = 311u.
So moles of nalorphene :
So the required weight of water is 3.2 g.
Molar mass of benzoic acid = 7(12) + 6(1) + 2(16) = 122u.
We are given with the molarity of solution.
So mass of benzoic acid :
Hence the required amount of benzoic acid is 4.575 g.
We know that depression in freezing point of water will depend upon the degree of ionisation.
The degree of ionisation will be highest in the case of trifluoroacetic acid as it is most acidic among all three.
The order of degree of ionisation on the basis if acidic nature will be:- Trifluoroacetic acid > Trichloroacetic acid > Acetic acid.
So the depression in freezing point will be reverse of the above order.
Firstly we will find the Vant's Hoff factor the dissociation of given compound.
So we can write,
Putting values of Ka and C in the last result, we get :
At equilibrium i = 1 - a + a + a = 1 + a = 1.0655
Now we need to find the moles of the given compound CH3CH2CHClCOOH.
So, moles =
Thus, molality of the solution :
Now we will use :
Firstly we need to calculate molality in order to get vant's hoff factor.
So moles of CH2FCOOH :
We need to assume volume of solution to be nearly equal to 500 mL. (as 500 g water is present)
Now, we know that :
Now for dissociation constant :-
Put values of C and a in the above equation, we get :
Firstly we will find number of moles of both water and glucose.
Moles of glucose :
and moles of water :
Thus vapour pressure of water after glucose addition = 17.44 mm of Hg
We know that :
We are given value of P and k, so C can be found.
Hence solubility of methane in benzene is .
For calculating partial vapour pressure we need to calculate mole fractions of components.
So number of moles of liquid A :
and moles of liquid B :
Mole fraction of A (xA) :
and mole fraction of B (xB) :
Now, Ptotal = PA + PB
Thus vapour pressure in solution due to A =
0 11.8 23.4 36.0 50.8 58.2 64.5 72.1
0 54.9 110.1 202.4 322.7 405.9 454.1 521.1
632.8 548.1 469.4 359.7 257.7 193.6 161.2 120.7
632.8 603 579.5 562.1 580.4 599.5 615.5 64.18
Plot this data also on the same graph paper. Indicate whether it has positive deviation or negative deviation from the ideal solution.