12th Chemistry Exam Questions of Chapter 2

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12th chemistry Chapter 2-Solutions in chemistry

12th chemistry guide exam Important question based on CBSE board curriculum and corresponding to the recent 12 class Chemistry syllabus in text questions.
By rehearsing these Class 12 significant inquiries, understudies will actually want to rapidly survey every one of the thoughts shrouded in the part and plan for the Class 12 Yearly assessments as well as other selection tests like NEET and JEE.

Check our 12th Chemistry exam solution of chapter 1 click here.

What is the significance of Henry’s Law constant KH ? (Chemistry book)

Henry’s Law constant (KH) helps in comparing the relative solubilities of different gases in the same solvent (e.g. water). In general, the lesser the value of KH, the more the solubility of a gas.

Why are aquatic species more comfortable in cold water in comparison to warm water? (Chemistry book)

In contrast to warm water, cold water is more comfortable for aquatic animals. This is due to the fact that when temperature rises, solubility of any gas in water diminishes. Compared to warm or hot water, cold water has a higher oxygen solubility. Because respiration requires oxygen, aquatic creatures may breathe easier in colder water than in warmer water because colder water contains a higher concentration of oxygen. As a result, they prefer cold water to warm water for comfort.

Why is the vapour pressure of an aqueous solution of glucose lower than that of water?(Chemistry book)

Liquid evaporation occurs at the surface. The liquid will evaporate more quickly the more surface area that is available. Glucose is no longer a volatile substance. It takes up a specific amount of the water’s surface. This implies that less water evaporates from the surface and less water vapor is present.

12th chemistry guide

How does sprinkling of salt help in clearing the snow-covered roads in hilly areas? Explain the phenomenon involved in the process(Chemistry book)

The phenomena of a liquid’s freezing point being lowered due to the presence of non-volatile impurities is what causes snow on snow-covered roadways to melt. Snow melts more easily when salt (sodium chloride) is added because it reduces the water’s freezing point temperature.

What is a “semi-permeable membrane”?(Chemistry book)

Semi-permeable membrane refers to those that only permit solvent molecules to pass through them. Seemingly endless sheets or films, the membranes are. Here, the only solute molecules that can pass through are those of the solvent; larger solute molecules cannot.

Explain the terms ideal and non-ideal solutions in the light of forces of interactions operating between molecules in liquid solutions.(Chemistry book)

In the case of ideal solution:

(i) The forces of interaction of the components in the solution are the same as in pure components i.e. A….. B interactions are the same as A….. A and B….B. interactions.

(ii) There is no change in volume on mixing the components i.e. ΔVmixing = 0.

(iii) There is no change in ΔH upon mixing the components i.e. ΔHmixing = 0.

(iv) Components obey Raoult’s Law at all temperatures and concentrations i.e.

PA = PAχ; PB = PBχB

In case of non-ideal solution:

(i) The forces of interaction of the components in the solution different from those present in pure components i.e. A….B interactions are different from A….. A and B…. B interactions.

(ii) There is a change in volume on mixing the components i.e. ΔVmixing ≠ 0

(iii) There is a change in ΔH on mixing the components i.e. ΔHmixing ≠ 0.

(iv) Components deviate from Raoult’s Law i.e.

PA ≠ PAχ; PB ≠ PBχB

Why is it not possible to obtain pure ethanol by fractional distillation? What general name is given to binary mixtures which show deviation from Raoult’s law and whose components cannot be separated by fractional distillation? How many types of such mixtures are there?(Chemistry book)

  • A mixture of ethanol and water is generally obtained when we prepare it commercially with the help of alcoholic fermentation.
  • The two liquids are completely miscible with each other. Their boiling points are 351 K and 373K respectively. Since the two liquids differ in their boiling points by more than 20°, they should be easily separated by a fractional distillation process.
  • However, during the operation, a stage is reached when we get a liquid mixture containing 95 percent ethanol and 5 percent water. This constitutes an azeotropic mixture also called a constant boiling mixture. Both alcohol and water start boiling together at a temperature which is close to the boiling point temperature of alcohol.

The azeotropic mixture shows a positive deviation from Raoult’s Law. In fact there are two types of azeotropic mixtures.

(a) Azeotropic mixture which shows positive deviation from Raoult’s Law (Minimum boiling azeotrope)

(b) Azeotropic mixture which shows negative deviation from Raoult’s Law (Maximum boiling azeotrope)

When kept in water, raisins swell in size. Name and explain the phenomenon involved. Give three applications of the phenomenon.(Chemistry book)

This happens due to a phenomenon known as osmosis. When the reisin is kept in water, it swells in size. Actually water is a hypotonic solution while the liquid or fluid inside the raisin is of hypertonic nature. The outer wall of the raisin acts as a semipermeable membrane. There is an osmosis of water molecules inside the raisin through this membrane and the raisin slowly swells in size.

Applications of osmosis:

  1. In animals circulation of water to all parts of the body takes place due to osmosis.
  2. Osmosis helps in plant growth and germination of seeds.
  3. When the dried fruits and vegetables are placed in water, they slowly swell because of osmosis.

Discuss the biological and industrial importance of osmosis.(Chemistry book)

Biological importance of osmosis

(i) Osmosis plays a significant role in the absorption of water by plant roots from the soil and its movement to different parts of the plant body.

(ii) When placed in water containing less than 0.9% (mass/volume) salt, blood cells collapse due to loss of water by osmosis.

(iii) In animals circulation of water to all parts of the body takes place due to osmosis.

(iv) Osmosis helps in plant growth and germination of seeds.

The industrial importance of osmosis

(i) The phenomenon of osmosis is also useful in some industrial processes. It is employed commercially for the desalination of seawater so that it may become useful for drinking purposes.(reverse osmosis)

(ii) The Reverse Osmosis process is very popular for the purification of drinking water in households.

How can you remove the hard calcium carbonate layer of the egg without damaging its semipermeable membrane? Can this egg be inserted into a bottle with a narrow neck without distorting its shape? Explain the process involved.(Chemistry book)

The hard layer of egg white in colour, consists of calcium carbonate. It can be removed by placing the egg in dilute hydrochloric acid for some time. It dissolves calcium carbonate, leaving behind the egg without damaging its soft semipermeable membrane.

The size of the egg can be reduced or it shrinks by placing it in saline water (contains NaCl) for some time. The fluid from the egg slowly escapes and passes into saline water which is at higher osmotic pressure (hypertonic in nature). Now, the egg with reduced size can be inserted in a bottle with a narrow neck. If the bottle contains water, the egg will regain its original shape and size due to the osmosis of water (hypotonic) through the semipermeable membrane.

Why is the mass determined by measuring a colligative property in case of some solutes are abnormal? Discuss it with the help of the Van’t Hoff factor.(Chemistry book)

Certain solutes do not behave normally in solution in the sense that they may either undergo dissociation or association. As a result, the number of solute particles in the solution changes.

Since the colligative properties are linked with the number of particles, they show abnormal results. In the same way, the molecular masses of these solutes also show abnormal results.

The exact behaviour of the solute in a solution and the extent of association or dissociation can be expressed in terms of Van’t Hoff factor (i).

i = Normal/ calculated molecular mass/ Observed molecular mass.

or i = Observed colligative properties/ Normal colligative properties.

  • If i = 1 , solute behave normally in the solution
  • If i > 1 , solute undergo dissociation in solution
  • If i < 1 , solute undergo association in solution

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