SURFACE CHEMISTRY Quiz-9

SURFACE CHEMISTRY QUIZ-9

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IIT JEE exam which consists of JEE Main and JEE Advanced is one of the most important entrance exams for engineering aspirants. The exam is held for candidates who are aspiring to pursue a career in the field of engineering and technical studies. Chemistry is important because everything you do is chemistry! Even your body is made of chemicals. Chemical reactions occur when you breathe, eat, or just sit there reading. All matter is made of chemicals, so the importance of chemistry is that it's the study of everything..

Q1.526.3 mL of 0.5 m HCl is shaken with 0.5 g of activated charcoal and filtered. The concentration of the filterate is reduced to 0.4 m. The amout of adsorption (x/m) is

•  3
•  6
•  8
•  4

Solution
(d). Mass of HCl acid adsorbed by 10 g charcoal =526.3×10^(-3) (0.5-0.4)×38≈2 (Mw of HCl=38 g mol^(-1)) The amount of adsorption x/m=2/0.5=4

Q2.  In an experiment, addition of 5.0 mL, of 0.006 M BaCl_2 to 10.0 mL of arsenic sulphite sol just causes the complete coagulation in 34 h. The flocculating value of the effective ion is :

•  2
•  3
•  4
•  5

Solution
(a). As2S3 sol is negatively charged owing to preferential adsorption of S^(2-) ions. Cation would be effective ion in coagulation Flocculating value = millimole of the effective ion per litre of sol =(5×0.006×10^3)/(5+10)=2

Q3.The coagulation of 100 mL of a colloidal sol of gold is completely prevented by addition of 0.03 g of Haemglobin to it before adding 1 mL of 10% NaCl solution. Calculate the gold number of Haemoglobin

•   4
•  8
•  3
•  9

Solution
(c). Haemoglobin added to 100 mL of gold sol to prevent coagulation by 1 mL of 10% NaCl=0.03 g=30 mg Haemoglobin required to be added to 10 mL of gold sol to prevent coagulation by 1 mL of 10% NaCl sol=3 mg Therefore, gold number of haemoglobin =3

Q4. From the given following sol how many can coagulate the haemoglobin sol? Fe(OH)3,Ca(OH)2,Al(OH)3, starch, clay, As2S3,CdS, basic dye

•  1
•  3
•  4
•  8

Solution
(c). Haemoglobin is positively charged sol. Hence the sol with negative charge can coagulate haemoglobic, i.e., starch, clay, As2S3,CdS

Q5.For the coagulation of 500 mL of arsenious sulphide sol, 2 mL of 1M NaCl is required. What is the folcculation value of NaCl?

•  3
•  2
•  5
•  4

Solution
 (d). 2 mL of 1 M NaCl contains NaCl=2/1000=2 mmol Thus 500 mL of As_2 S_3 sol require NaCl for complete coagulation = 2 mmol Hence 1 L, i.e., 1000 mL of the sol require NaCl for complete coagulation = 4 mmol Therefore, flocculation value of NaCl=4

Q6. In an adsorption experiment, a graph between log⁡(x/m) versus log⁡P was found to be linear with a slope of 45°. The intercept on the y axis was found to be 0.301. Calculate the amount of the gas adsorbed per gram of charcoal under a pressure of 3.0 atm

•  4
•  2
• 6
•  8

Solution
(c). log⁡(x/m)=log⁡(K)+(1/n)log⁡P

Q7.A chemist studied the phenomenon of adsorption by putting blood charcoal in KCl solution. He observed difference in the behaviour with dilute KCl solution and with concentrated KCl solution. He also studied the adsorption of different gases on solid adsorbent and the effect of temperature on adsorption. He put forward a mathematical relationship relating x/m with equilibrium pressure. Q. Which of the following is correct?

•  Adsorption is always exothermic?
•  Adsorption is always endothermic
•  Physical adsorption is endothermic whereas chemisorptions is exothermic.
•  Chemical adsorption is endothermic whereas physical adsorption is exothermic

Solution
(a). Adsorption is always exothermic

Q8.Colloidal dispersion have been classified into different types depending upon the physical state of the dispersed phase and the dispersion medium. They are prepared in the industry or in the laboratory by a number of methods and then purified. The protective action of lyophilic colloids was studied by zsigmondy and he introduced a term called gold number. Q. Which of the following does not form a lyophilic colloid?

•  Rubber dissolved in benzene 1
•  White of the egg dissolved into water
•  Common salt added into benzene
•  Stannous chloride solution added to gold chloride solution

Solution
(d). SnCl2+AuCl3 react to form gold sol which is a lyophobic sol.

Q9.The catalytic activity and colloidal nature of a substance are surface phenomenon. Both these properties depend upon the property of adsorption. Adsorption may be physisorption or chemisorption. Adsorption is spontaneous and always leads to decrease in entropy along with evolution of heat. Chemisorption is irreversible with temperature, unilayer, specific and directional. Adsorbate molecules adsorb on catalyst surface and thus, lowers the energy of activation of reaction to provide a new pathway for reaction. In colloidal state dispersed phase particles possess the adsorption characteristics at the interface. Q.Select the correct statements : 1. Adsorption is spontaneous at all the temperatures. 2. Gases having high critical temperature possess more tendency for adsorption. 3. An adsorbent possesses more tendency for adsorption if it is in colloidal state. 4. Chemical adsorption first decreases with increase in temperature and then increases. 5. Water molecules are adsorbed in CaCl_2 (s).

•  1,2,3,4,5
•  2,3,4
•  1,2,3,4
•  2,3

Solution
(b). 1. Adsorption decreases with increase in temperature but ∆G= -ve at high temperature. ∆H= -ve and ∆S= -ve,thus T∆S= -ve ∴ ∆G= ∆H-T∆S= -ve-(-ve)=less negative 2. Gases having high critical temperature are easily liquefiable due to higher forces of attractions among molecules and thus, also show more adsorption. 3. Adsorption extent of an adsorbent is more if its surface area is more. 4. Chemisorption requires energy of activation. 5. H2O is absorbed on CaCl2 and nor adsorbed.

Q10. Lyophilic sols are

•  Irreversible sols
•  They are prepared from inorganic compounds
•  Coagulated by adding electrolytes
• Self-stabilising

Solution
(d). Lyophilic sols are self stabilizing because these sols are reversible and are highly hydrated in the solution.

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