11th Class Chemistry Chapter nine Short Questions with Answers Solved

Question: 1

One molal solution of urea is more dilute as compared to its one molar solution.Why?

Answer: 1

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One molal solution contains one mole of urea per kg of solvent, while one mole solution contains one mole of urea per one dm³ Of solution.In one molal solution amount of water is greater than one molar solution because amount of solution included in it.

Question: 2

Define percentage weight/weight.Give an example?

Answer: 2

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Question: 3

What is critical solution temperature? Give the critical solution temperature of phenol water system?

Answer: 3

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Critical Temperature: The temperature at which two conjugate solutions merge into each other to form homogeneous mixture is called critical solution temperature or consulate temperature.

Phenol-Water system has critical temperature of 65.9°C at which two conjugate solution merge into one another.

Question: 4

One molal solution of urea in water is dilute as compared to one molar solution of urea but the number of practices of solute is same.Justify it?

Answer: 4

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Both one molar and one molal urea solution contains equal number of molecules(6.022x10²³ ).Number of water molecules are different in both cases.One molal solution contains 1000g or 55.5 moles of water.One Molar solution has less number of water molecules than one molal.

Question: 5

Define azeotropic mixture.Give two examples?

Answer: 5

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Azeotropic Mixtures: The liquid mixtures which boil at constant temperature and distil over without changes in composition like a pure compound at any temperature is called azeotropic mixtures.e.g.HCI azeotropic mixture with water.

Question: 6

Calculate percentage by weight of NaCI when 2g of NaCI is dissolved in 20g of water?

Answer: 6

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Mass of NaCl =2g

Mass of water =20g

Mass of solution= 20+2=22g

%by weight of NaCl=2/22x100=9.09%

Question: 7

The concentration in terms of molality is independent of temperature but molarity depends upon temperature .Why?

Answer: 7

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In molality mass of solvent is taken.Mass us independent of temperature.In molarity volume of solution is take.Volume changes by change in temperature.

Question: 8

Answer: 8

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Question: 9

Define consulate solution temperature with example (what is consulate temperature)?

Answer: 9

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Consulate Temperature: The temperature at which two conjugate solutions merge into each other to form homogeneous mixture is called critical solution temperature or consulate temperature.e.g Water -Aniline has consulate temperature 167°C with 15% H₂O.

Question: 10

Polar solids are not dissolved in on-non-polar solvent,give reason?

Answer: 10

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There is a general principal that "like dissolve like".That;s why polar compounds are not dissolve in non-polar solvent because their nature matches with each other.

Question: 11

Differentiate between zeotropic and azeotropic mixture?

Answer: 11

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Zeotropic Mixtures: The liquid mixtures which distills with change in composition is called zeotropic mixtures,e.g.Methyl Alcohol-water solution.

Azeotropic Mixtures: The liquid mixtures which boil at constant temperature and distill over without changes in composition like a pure compound at any temperature is called azeotropic mixtures.eg, HCI formsazeotropic with water.

Question: 12

Define fractional crystallization.How is it useful?

Answer: 12

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Fractional Crystallization: The separation of solid substances from a solution one by one on cooling is called fractional crystallization.This technique is used for separation of impurities from sample.

Question: 13

Differentiate between ideals and non-ideal solutions?

Answer: 13

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Ideal Solution:

The solutions which obey Raoult's law are called ideal solution
In these solution, enthalpy change is zero.

Question: 14

Give conjugate solution with one example.

Answer: 14

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Each liquide layer of solution of two liquids which are not miscible with each other is a saturated solution of the other liquid.Such solutions are called conjugated solutions.On shaking equal volumes of water and ether, two layers are formed which is example of conjugated solution.

Question: 15

Why the solubility of glucose increases on increasing temperature?

Answer: 15

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When glucose is dissolve in water it show endothermic heat of solution.Solute molecules separate from each other to dissolve in solvent.This process required energy.So when temperature is increased solubility also increases.

Question: 16

Differentiate between continuous and discontinuous solubility curves?

Answer: 16

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Continuous Solubility Curve: These are smooth curves and do not show any sharp break points.(Continuous increase or decreases in solubility with temperature.e.g.Solubility curves of KCIO₃,K₂Cr₂O₇ Etc.

Discontinuous Solubility Curves: These are not smooth and shows sudden breaks due to sudden changes in solubilities.e.g.Solubility curves of Na₂SO₄,CaCl_{2 etc.}

Question: 17

Define solubility curve.Name its two types?

Answer: 17

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Solubility Curve: A graphical representation between temperature and solubility of a substance is called solubility curve.These are of two types:

Continuous solubility curve
Discontinuous solubility cure

Question: 18

What is upper consulate temperature and give one example?

Answer: 18

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The temperature of 65.9°C at which two conjugate solutions merge into one another is called critical solution temperature or upper consulate temperature .For Example 34% phenol and 66% water solution.

Question: 19

Why the non-ideal solutions do not obey the Raoult's law?

Answer: 19

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Mnay solutions do not behave ideally as they show deviation from Raoult's law due to difference in their molecular structure I.e. Size, shape and intermolecular forces.During their formation change in volume and enthalpy take place.Hence they show deviation from ideality.

Question: 20

Give two examples of liquid solution?

Answer: 20

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Alcohol in water
Benzene in toluene

Question: 21

The total volume of the solution by mixing 100 cm³ Of water 100 cm³ Of alcohol may not be equal to 200 cm³ Justify it?

Answer: 21

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Alcohol and water are mix in all proportions.However, the properties of such solutions are not strictly additive.Generally, the volume decreases ,mixing but in some cases it increases.Heat may be evolved or absorbed during the formation of such solutions.

Question: 22

Define solubility giving one example?

Answer: 22

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The solubility is defined as the concentration of the solute in the solution when it is in equilibrium with the solid substance at a particular temperature. Solubility is expressed in terms of number of grams of solute in 100g of solvent. At a particular temperature, saturated solution of NaCl in water at O° C contains 37.5g NaCl in 100g of water.

Question: 23

Fractional crystallization technique is used to purify the chemical products.Justify?

Answer: 23

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The separation of solid substance from a solution one by one on cooling is called fractional crystallization.Solubilities depends upon temperature.

E.g.Solubility of KNO₃ Rapidly changes with temperature but solubility of KCI and Kbr changes gradually.Thus one substance may precipitate earlier by cooling, leaving behind others.

Question: 24

Can sugar cannot be dissolved in benzene.Give reason?

Answer: 24

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Can-sugar is apolar covalent substance and it is soluble in polar solvent like water. Sugar dissolve in water due to the formation of H-bonding between solute-solvent,but not in benzene.As we simply say that solubility based upon principle"Like dissolves like".

Question: 25

Describe that NaCI and KNO₃ Are used to lower the melting point of ice?

Answer: 25

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NaCI and KNO₃are used as antifreeze.They depress the freezing point of ice and it melts. This method is used to melt the ice from the roads in winter.

Question: 26

Colligative properties are obeyed when the solute is non-electrolyte and also when the solutions are dilute.Explain?

Answer: 26

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Colligative properties depend upon number of solute, particles in solution of non-electrolyte. Solute do not ionize in solution and its number of particles remain same. E.g1 mole of urea produces 3.02x10²³ Particles in solution.When solution is dilute, less number of solute particles far away from each other and they behave independently and colligative properties are obeyed.

Question: 27

Boiling points of liquid are increased when solute is added to them.Give reason?

Answer: 27

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Because the vapour pressure of solvent decrease due to the pressure of solute.Therefore,we have to supply high temperature in order to equalized the vapour pressure of solvent to external pressure to boil it. This results in the increase of boiling point of solvent in the presence of solute.

Question: 28

Why is the vapour pressure of a solution less than pure solvent?

Answer: 28

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In pure solvent all the surface of solvent is covered by solvent molecules.But when a solute is added to it from a solution.Some surface is occupied by solute particles. Hence escaping tendency of solvent is decreases and thus vapour pressure of solution also lowered.

Question: 29

In summer the antifreeze solutions protect the radiations from boiling over.How?

Answer: 29

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The boiling point of liquid is increased by the addition of solute such as ethylene glycol in water.Therefore in summer the antifreeze liquids protect the water in car radiators from over boiling. Similarly the addition of a solute in water depress its freezing point. During winter it protect a car by preventing the liquid from freezing in radiators.

Question: 30

Why some properties are called colligative properties?

Answer: 30

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Colligative properties are called so because these depend upon the number of solute particle in definite amount of solvent and independent on the nature of solute.For example lowering of vapour pressure of water, caused by the addition of 6g of urea, 18 g of glucose and 34.2 g of sucrose is same although the solute particles are of different nature but their numbers are same.

Question: 31

NaCl and KNO₃ Lowers the melting point of ice.Give reason?

Answer: 31

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When NaCl andKNO₃ Is added to H₂O , is vapour pressure is lowered. Due to lowering of vapour pressure, solution freezes below than the freezing point of water.Hence NaCl and KNO₃ Is used to lower the melting point of ice.

Question: 32

Define Colligative properties.Name important colligative properties?

Answer: 32

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Colligative Properties: The properties of a solution which is based upon the number of solute particles and independent of the nature of solute is called colligative properties.Name of some colligative properties are:

Lowering of vapour pressure
Depression in freezing point
Elevation in boiling point
Osmotic pressure

Question: 33

Give the condition of colligative properties?

Answer: 33

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There are following conditions for colligative properties:

Solution must be dilute.
Solute must be non-volatile.
Solute must be non-electrolyte.

Question: 34

Beckmann's thermometer is used to note the depression in freezing point.Explain with reason?

Answer: 34

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There is a very small difference between freezing point of pure solvent and its dilute solution.Ordinary thermometer can read up to 0.5K.Hence theses cannot differentiate between freezing point of pure solvent and solution.

Beckmann' sthermometer can read up to 0.01K.Hence it cn exactly measure the freezing point of pure solvent and solution.

Question: 35

State ebullioscopeic constant and cryoscopic constant?

Answer: 35

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Ebullioscopic constant: It is elevation in boiling point which is produced,when 1 mole of solute is dissolved in 1 kg of solvent.It is denoted by K_b. Its value is 0.52C° for water.

Cryoscopic constant: It is depression in freezing point which is produced when q mole of solute is dissolved in 1 kg of solvent. It is denoted by K_f

Its value is 1.86 C° for water

Question: 36

What are the names major parts of apparatus used in Landsberger's method for elevation of boiling point?

Answer: 36

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An inner tube with a hole in its side.This tube is graduated.
A boiling flask which send the solvent vapours into the graduated tube through a rosehead..
An outer tube, which receives hot solvent vapours coming from the side hole of the inner tube.
A thermometer which can read up to 0.01K.

Question: 37

Why hydration energy of Na⁺ Ion is less than Li⁺ Ion?

Answer: 37

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Hydration energy of an ion depends upon two parameters .

Ionic Radii
Charge density

Greater the ionic radii of monopositive ions, smaller is the heat of hydration and vice versa. Hence Na⁺ Has greater size than Li⁺ That's why its heat of hydration is low.

Question: 38

Why ethylene glycol is added in radiator of Automobile?

Answer: 38

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The most important application of this phenomenon is the use of antifreeze in the radiator of an automobile.The solute is ethylene glycol, which is not only completely miscible with water but has a very low vapour pressure and non-volatile in character. When mixed with water it lowers the freezing point a swell as raised the boiling point.

Question: 39

Define "heat of solution" and "hydration energy"?

Answer: 39

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The quantity of heat energy that is absorbed or released when a substance forms solution, is termed as heat of solution.

When ionic compound is dissolved in water, the first step is the separation of ions from solid and second step is separated ions are surrounded by solvent molecules.A Hydrated ion is attracted by the solvent dipoles and energy is released, so second step is exothermic. The energy given out by the second step is known as the hydration energy .

Question: 40

The freezing points are depressed due to the presence of solutes.Five reason?

Answer: 40

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Freezing point of a substance also related to its vapour pressure.it is a temperature at which there is equilibrium between a solid and a liquid. At freezing point, vapour pressure of liquid and solid phase is same.When some solute is added to solvent, its vapour pressure decreases and freezing point also decreases.

Question: 41

Define molal freezing point constant giving example.

Answer: 41

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It is depression of freezing point, when one mole of non-volatile and non-electrolyte solute is dissolved in one kg of solvent.

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11th Class Chapter nine Chemistry Short Questions

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