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Chemistry 3 Marks Question

Surface Chemistry · CBSE STD 12 Science (CBSE - English Medium). 56 questions.

Questions · Page 2 of 2

3 Marks Question

Question 513 Marks
Do the vital functions of the body such as digestion get affected during fever? Explain your answer.
Answer
The rate of an enzyme reaction is maximum at a particular temperature range, called optimum temperature. On either side of the optimum temperature, the enzyme activity decreases. The optimum temperature range for enzymatic activity is 298-310K. Normal human body temperature being 310K is suited for enzyme-catalysed reactions. If a person is suffering from fever, the temperature will be over 310K. This will adversely affect the enzymatic reactions.
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Question 523 Marks
$SnO_2$ forms a positively charged colloidal sol in acidic medium and a negatively charged sol in the basic medium. Why? Explain.
Answer
$SnO_2$ is amphoteric in nature. It reacts with acids such as $HCl,$ to form $SnCl_4$ in the solution.
The common $Sn^{4+}$ ions are adsorbed on the surface of $SnO_2$ particles to give a positively charged colloidal sol. $\text{SnO}_2+4\text{HCl}\rightarrow\text{SnCl}_4+2\text{H}_2\text{O}$$\text{SnO}_2 +\text{Sn}^{4+}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ \ \ }(\text{SnO}_2):\text{Sn}^{4+}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Positively charged sol}$
$SnO_2$ is amphoteric in nature. It reacts with acids such as $HCl,$ to form $SnCl_4$ in the solution.
The common $Sn_4+$ ions are adsorbed on the surface of $SnO_2$ particles to give a positively charged colloidal sol. $\text{SnO}_2+2\text{NaOH}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }\text{Na}_2\text{SnO}_3+\text{H}_2\text{O}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Sodium stannate}$ $\text{SnO}_2+\text{SnO}^{2-}_3\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }(\text{SnO}_2):\text{SnO}^{2-}_3\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Negatively charged sol}$
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Question 533 Marks
Give four examples of heterogeneous catalysis.
Answer
  1. Oxidation of sulphur dioxide to form sulphur trioxide. In this reaction, Pt acts as a catalyst
$2\text{SO}_{2(\text{g})}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \text{Pt}_{(\text{s})}\ \ \ \ \ \ \ \ }2\text{SO}_{3(\text{g})}$
  1. Formation of ammonia by the combination of dinitrogen and dihydrogen in the presence of finely divided iron.
$\text{N}_{2(\text{g})}+3\text{H}_{2(\text{g})}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \text{Fe}_{(\text{s})}\ \ \ \ \ \ \ \ }2\text{NH}_{3(\text{g})}$

This process is called the Haber's process.
  1. Oswald's process: Oxidation of ammonia to nitric oxide in the presence of platinum.
$4\text{NH}_{3(\text{g})}+5\text{O}_{2(\text{g})}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \text{Pt}_{(\text{s})}\ \ \ \ \ \ \ \ }4\text{NO}_{(\text{g})}+6\text{H}_2\text{O}_{(\text{g})}$
  1. Hydrogenation of vegetable oils in the presence of Ni.
$\text{Vegetable }\text{oil}_{(1)}+\text{H}_{2(\text{g})}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \text{Ni}_{(\text{s})}\ \ \ \ \ \ \ \ }\text{Vegetable }\text{ghee}_{(\text{s})}$
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Question 543 Marks
What type of colloidal sols are formed in the following:
  1. Sulphur vapours are passed through cold water.
  2. White of an egg is mixed with water.
  3. Soap solution.
Answer
  1. Multimolecular because sulphur molecules associate together to form multimolecular colloids.
  2. Macromolecular because protein molecules present in the white of the egg are macromolecules soluble in water.
  3. Associated because RCOO– ions associate together to form micelles.
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Question 553 Marks
Distinguish between the meaning of the terms adsorption and absorption. Give one example of each.
Answer
 
Absorption
Adsorption
1.
It is the phenomenon in which the particles of gas or liquid get uniformly distributed throughout the body of the solid.
It is the phenomenon of higher concentra-tion of particles of gas or liquid on the surface than in the bulk of the solid.
2.
The concentration is the same through the material. Therefore, it is a bulk phenomenon.
The concentration on the surface of the adsorbent is different from that in the bulk. Therefore, it is a surface phenomenon
3.
Absorption occurs at uniform rate.
Adsorption is rapidly in the beginning and its rate slow.ly increases.
Example of adsorption: $NH_3,$ adsorbed by charcoal, $H_2O$ adsorbed by silica, ink adsorbed by chalk.
Example of absorption: $NH_3$ absorbed by water, water absorbed by anhydrous $CaCl_2,$ water absorbed by a sponge.
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Question 563 Marks
What are lyophilic and lyophobic sols? Give one example of each type. Why are hydrophobic sols easily coagulated?
Answer
  1. Lyophilic sols:
Colloidal sols that are formed by mixing substances such as gum, gelatin, starch, etc. with a suitable liquid (dispersion medium) are called lyophilic sols. These sols are reversible in nature i.e., if two constituents of the sol are separated by any means (such as evaporation), then the sol can be prepared again by simply mixing the dispersion medium with the dispersion phase and shaking the mixture.
  1. Lyophobic sols:
When substances such as metals and their sulphides etc. are mixed with the dispersion medium, they do not form colloidal sols. Their colloidal sols can be prepared only by special methods. Such sols are called lyophobic sols. These sols are irreversible in nature. For example: sols of metals.

Now, the stability of hydrophilic sols depends on two things- the presence of a charge and the salvation of colloidal particles. On the other hand, the stability of hydrophobic sols is only because of the presence of a charge. Therefore, the latter are much less stable than the former. If the charge of hydrophobic sols is removed (by addition of electrolytes), then the particles present in them come closer and form aggregates, leading to precipitation.
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