CBSE Class 12 Chemistry Solutions Worksheet Set B

Read and download free pdf of CBSE Class 12 Chemistry Solutions Worksheet Set B. Download printable Chemistry Class 12 Worksheets in pdf format, CBSE Class 12 Chemistry Solutions Worksheet has been prepared as per the latest syllabus and exam pattern issued by CBSE, NCERT and KVS. Also download free pdf Chemistry Class 12 Assignments and practice them daily to get better marks in tests and exams for Class 12. Free chapter wise worksheets with answers have been designed by Class 12 teachers as per latest examination pattern

Solutions Chemistry Worksheet for Class 12

Class 12 Chemistry students should refer to the following printable worksheet in Pdf in Class 12. This test paper with questions and solutions for Class 12 Chemistry will be very useful for tests and exams and help you to score better marks

Class 12 Chemistry Solutions Worksheet Pdf


Very Short Answer

Question. Define isotonic solutions?
Answer. 
Two solutions having same osmotic pressure at a given temperature is called isotonic solutions.

Question. How can we obtain colligative properties?
Answer. 
Colligative properties are obtained by assuming that the non-volatile solute is neither associated nor dissociated.

Question. What is non-ideal solution?
Answer. 
When a solution does not obey Raoult’s law over the entire range of concentration then it is called non-deal solution.

Question. Who gave the quantitative relationship between vapour pressures of liquid solutions?
Answer. 
Francois Marte Raoult gave the quantitative relationship between vapour pressures of liquid solutions.

Question. What is ideal solution?
Answer. 
The solutions which obey Raoult’s law over the entire range of the concentration is known as ideal solution.

 

Short Answer

Question. What are the properties of the solutions which are connected with the decrease of vapour pressure?
Answer. 
There are many properties of the solutions which are connected with the decrease of vapour pressure are:
1. Relative lowering of vapour pressure of the solvent.
2. Depression of freezing point of the solvent.
3. Elevation of boiling point of the solvent.
4. Osmotic pressure of the solution.

Question. What do you understand by Raoult’s law?
Answer. 
Raoult’s law states that for a solution of volatile liquids, the partial vapour pressure of each component of the solution is directly proportional to its mole fraction present in the solution.

Question. What do you mean by the Dalton’s law of partial pressures?
Answer. 
Dalton’s law of partial pressures states that the total pressure over the solution phase in the container will be the sum of the partial pressures of the components of the solution.Real gases do not obey Dalton's law of partial pressures. It is because these gases do not behave ideally and violate some of the rules of the kinetic theory of gases. Real gases behave ideally only under circumstances where the pressure is low and the temperature is high.

Question. Define abnormal molar masses?
Answer. 
Molar masses that are lower or higher than expected values when calculated are called abnormal molar masses. Abnormal molar masses depends upon the total number of moles particles either after dissociation or association of solute molecules in solvent or solution.

Question. What do you mean by the colligative properties?
Answer. 
All these properties depend on the number of solute particles irrespective of their nature relative to the total number of particles present in the solution, so such properties are

 

Long Answer

Question. State the difference between osmosis and reverse osmosis?
Answer. 

1. Osmosis refers to a process by which water molecules of a solvent tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one whereas reverse osmosis refers to a process by which water molecules of a solvent passes through a semipermeable membrane in the direction opposite to that of natural
osmosis when subjected to a hydrostatic pressure greater than the osmotic pressure.
2. The osmosis occurs through a potential gradient whereas reverse osmosis occurs against the potential gradient.
3. Osmosis is a natural process whereas reverse osmosis is an artificial process.
4. Absorption of water from the soil by roots and opening the stomata occurs due to osmosis whereas reverse osmosis is used in the waterpurification systems.
5. Osmosis occurs without an energy requirements whereas reverse osmosis needs energy to supply a pressure

Question. Distinguish the between positive deviation and negative deviation?
Answer. 

1. In positive deviation vapour pressure of solution and partial pressure of the components are more than those expected by the Raoult’s law whereas in negative deviation the vapour pressure of solution and partial pressure of the components are less than those expected by the Raoult’s law.
2. Positive deviation forms minimum boiling azeotrope whereas negative deviation forms maximum boiling azeotrope.
3. In positive deviation on mixing intramolecular attraction decreases whereas in negative deviation on mixing with the intramolecular attraction increases.
4. ΔHmix ≠ 0 and it is positive whereas ΔHmix ≠ 0 and it is negative.
5. ΔVmix = positive whereas ΔVmix = negative.

Question. State the difference between hydrostatic pressure and osmotic pressure?
Answer. 

1. Hydrostatic pressure is the pressure at any point of a non-flowing liquid due to the force gravity whereas osmotic pressure is the pressure required to prevent a solution from undergoing osmosis.
2. Hydrostatic pressure occurs in both pure solutions and homogenous solutions whereas osmotic pressure cannot be found in pure solutions.
3. Hydrostatic pressure is observed in non-flowing solutions whereas osmotic Pressure is observed in solutions where movement of solutes occurs.
4. Hydrostatic pressure is different in different levels of the same liquid whereas osmotic pressure is the same in everywhere of the liquid; thus, it is calculated considering the whole system.
5. In hydrostatic pressure, a semi-permeable membrane is not involved whereas in osmotic pressure, a semi-permeable membrane is involved.

Question. Distinguish between ideal solution and non-ideal solution?
Answer. 

1. An ideal solution is a solution where interactions between molecules are identical between all the molecules in the solution whereas a non-ideal solution is a solution that has differences in the interactions between molecules of different components in the solution.
2. Ideal solutions have identical interactions between all the molecules of all components whereas non ideal solutions have solvent-solvent, solvent-solute
and solute-solute interactions.
3. The change in enthalpy when an ideal solution forms is zero or approximately zero whereas the change in enthalpy when a non-ideal solution forms is either a positive or negative value.
4. Highly dilute solutions can behave as ideal solutions whereas concentrated solutions behave as non-ideal solutions.

Question. State the difference between hypotonic and hypertonic?
Answer. 

1. Hypotonic solutions are solutions having lower osmotic pressures whereas hypertonic solutions are solutions having comparatively higher osmotic pressures.
2. Hypotonic solutions have a low concentration whereas hypertonic solutions have a high concentration.
3. Hypotonic environments cause cells to swell whereas hypertonic environments cause cells to shrink.
4. Hypotonic solutions are not helpful in food preservation whereas hypertonic solutions are helpful in food preservation since they kill microbes in the food package.
5. Hypotonic water concentration is high whereas hypertonic water concentration is low.

 

KEY CONCEPTS

Solution is the homogeneous mixture of two or more substances in which the components are uniformly distributed into each other. The substances which make the solution are called components. Most of the solutions are binary i.e., consists of two components out of which one is solute and other is solvent.
Ternary solution consists of three components
Solute ‐ The component of solution which is present in smaller quantity.
Solvent – The component of solution present in larger quantity or whose physical state is same as the physical state of resulting solution.
Types of solutions: Based on physical state of components solutions can be divided into 9 types.
Solubility ‐ The amount of solute which can be dissolved in 100grm of solvent at particular temp. to make saturated solution.

Solid solutions are of 2 types ‐
1. Substitutional solid solution e.g. Brass (Components have almost similar size)
2. Interstitial solid solution e.g. steel (smaller component occupies the interstitial voids)

 

Question. What do you mean by Henry’s Law? The Henry’s Law constant for oxygen dissolved in water is 4.34×104 atm at 25o C. If the partial pressure of oxygen in air is 0.2 atm, under atmospheric pressure conditions. Calculate the concentration in moles per Litre of dissolved oxygen in water in equilibrium with water air at 25o C.
Answer. Partial pressure of the gas is directly proportional to its mole fraction in solution at particular temperature.
PA α XA ; KH = Henry’s Law of constant
PA = KH ×A
KH = 4.34×104 atm
PO2 = 0.2 atm
Xo2 = PO2 / KH =0.2 / 4.34×104= 4.6×10‐6
If we assume 1L solution = 1L water
n water = 1000/18 = 55.5
XO2 = nO2 /(nO2+ n H2O ) ~ = nO2 /nH2O
nO2 = 4.6 X 10‐6 X 55.5 = 2.55 X 10‐4 mol
M = 2.55 X 10‐4 M

Question. What is Vant Hoff factor?
Answer. It is the ratio of normal molecular mass to observed molecular mass . H is denoted as ‘i’
i = normal m.m / observed m.m
= no. of particles after association or dissociation / no. of particles before

Question.  What is the Vant Hoff factor in K4[Fe(CN)6] and BaCl2 ?
Answer. 5 and 3

Question. Why the molecular mass becomes abnormal?
Answer. Due to association or dissociation of solute in given solvent .

Question. Define molarity, how it is related with normality ?
Answer. N = M x Basicity or acidity.

Question. How molarity is related with percentage and density of solution ?
Answer. M = P x d x10/M.M

Question. What role does the molecular interaction play in the solution of alcohol and water?
Answer. Positive deviation from ideal behavior .

Question. What is Vant Hoff factor , how is it related with
a. degree of dissociation b. degree of association
Answer. a. α=i – 1/n‐1 b. α = i ‐1 / 1/n ‐1

Question. Why NaCl is used to clear snow from roads ?
Answer. It lowers f.p of water

Question. why the boiling point of solution is higher than oure liquid
Answer. Due to lowering in v.p


HOTS

Question. Out of 1M and 1m aqueous solution which is more concentrated
Answer. 1M as density of water is 1gm/Ml

Question. Henry law constant for two gases are 21.5 and 49.5 atm ,which gas is more soluble .
Answer. KH is inversely proportional to solubility .

Question. Calculate the volume of 75% of H2SO4 by weight (d=1.8 gm/ml) required to prepare 1L of 0.2M
Answer.
Hint: M1 = P x d x 10 /98
M1 V1 = M2V2
14.5ml

Question. Why water cannot be completely separated from aqueous solution of ethyl alcohol?
Answer. Due to formation of Azeotrope at (95.4%)


SHORT ANSWERS (2 MARKS)

Q.1. How many grams of KCl should be added to 1kg of water to lower its freezing point to ‐8.00C (kf = 1.86 K kg /mol)
Answer. Since KCl dissociate in water completely L=2; m =
m= 8 / 2X1.86 = 2.15mol/kg.
Grams of KCl= 2.15 X 74.5 = 160.2 g/kg.

Q.2. With the help of diagram: show the elevator in boiling point colligative properties ?
Q.3. what do you mean by colligative properties, which colligative property is used to determine m.m of polymer and why?

Q.4. Define reverse osmosis, write its one use.
Answer. Desalination of water.

Q.5. Why does an azeotropic mixture distills without any change in composition.
Hint: It has same composition of components in liquid and vapour phase.

Q.6. Under what condition Vant Hoff’s factor is
a. equal to 1 b. less than 1 c. more than 1

Q.7. If the density of some lake water is 1.25 gm /ml and contains 92gm of Na+ ions per kg of water.
Calculate the molality of Na+ ion in the lake .
Answer. n = 92/23 = 4
m= 4/1 = 4m

Q.8. An aqueous solution of 2% non‐volatile exerts a pressure of 1.004 Bar at the normal boiling point of
the solvent . What is the molar mass of the solute .
Hint: P0
A – PA/P0
A = wB X mA / mB X wA
1.013 – 1.004 / 1.013 = 2X 18 /mB X 98
mB = 41.35gm/mol

Q.9. Why is it advised to add ethylene glycol to water in a car radiator in hill station?
Hint: Anti‐ freeze.

Q.10. what do you mean by hypertonic solution, what happens when RBC is kept in 0.91% solution of sodium chloride?

Q 11. (a). define the following terms.
1. Mole fraction
2. Ideal solutions
(b)15 g of an unknown molecular material is dissolved in 450 g of water. The resulting solution
frrezez at ‐0.34 0c . what is the molar mass of material? Kf for water= 1.86 K Kg mol‐1 .
Answer. 182.35 glmol

Q 12.(a) explain the following :
1. Henry’s law about dissolution of a gas in a liquid .
2. Boling point elevation constant for a solvent
(b)a solution of glycerol (C3h803) in water was prepared by dissolving some glycerol in in 500 g of water.
The solution has a boiling point of 100.42 0c . what mass of glycerol was dissolved to make this solution?
Kb for water = 0.512 k Kg mol‐1
(hint: atb = b*wb*1000/Mb*Wa
Answer. 37.73 gm

Q 13. 2 g of benzoic acid (c6h5cooh) dissolved in 25 g of benzene shows a depression in freezing point equal to 1.62 K . KF for benzene is 4.9 K Kg mol‐1. What is the percentage association of acid if it forms dimer in solution.
Answer. 99.2%

Q14. Osmotic pressure of a 0.0103 molar solution of an electrolite is found to be 0.70 atm at 270c .
calculate Vant Hoff factor.( R=0.082 L atom mol‐1 K‐1)
Answer. 2.76

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