Chemical Equilibrium

PHYSICAL CHEMISTRY XII (ALL)

IONIC f

EQUILIBRIUM

" A SPECIALLY DESIGNED KIT FOR LEARNING"

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CONTENTS THE KEY

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THEATLAS

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Basic layout of subject. A route map correlating different subtopics in coherent manner. A list of important terms in brief

GLOSSARY

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EXERCISE I

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Introductory problems to getfirsthand experience of problem solving.

PROFICIENCY TEST

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To check you newly acquired concepts.

BEWARE OF SNAKES

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A list of common mistakes made by students's.

EXERCISE II

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A collection of good problems.

EXERCISE III EXERCISE IV L

Basic principles of subjects. An outline of the topics to be discussed in class lectures.

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Test your objective skill. A collection of previous ten years JEE problems. Jj

THE KEY Fundamentals of Acids, Bases & Ionic Equilibrium Acids & Bases When dissolved in water, acids release H+ ions, base release OH" ions. Arrhenius Theory When dissolved in water, the substances which release (i) H+ ions are called acids (ii) OH - ions are called bases Bronsted & Lowry Concept Acids are proton donors, bases are proton acceptors Note that as per this definition, water is not necessarily the solvent. When a substance is dissolved in water, it is said to react with water e.g. HCl + H 2 0 -» H 3 0 + + CI" ; HCl donates H+ to water, hence acid. NH3 + H 2 0 NH4 + + OH" ; NH3 takes H+ from water, hence base. For the backward reaction, NH4+ donates H+, hence it is an acid; OH - accepts H+, hence it is base. NH3 (base) & NH4+ (acid) from conjugate acid base pair. Conjugate acid and bases To get conjugate acid of a given species add H+ to it. e.g. conjugate acid of N2H4 is N2H5+. To get conjugate base of any species subtract H+ from it. e.g. Conjugate base of NH3 is NH2~. Note: Although CI- is conjugate base of HCl, it is not a base as an independent species. In fact, anions of all strong acid likn r of H X O-» I T Y W U W E . 0

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Q.6.4 The equivalent point in a titration of 40.0 mL of a solution of a weak monoprotic acid occurs when 35.0 mL of a 0.10M NaOH solution has been added. The pH of the solution is 5.75 after the addition of 20.0 mL of NaOH solution. What is the dissociation constant of the acid? Q. 6.5 Phenol, C6H5OH, is a weak organic acid that has many uses, and more than 3 million ton are produced annually around the world. Assume you dissolve 0.515 g of the compound in exactly 1 OOrnL of water and then titrate the resulting solution with 0.123M NaOH. C6H5OH (aq) + OH" (aq) C6H5CT (aq) + H,O(0 What are the concentrations of all of thefollowingions at the equivalence point: Na+, H30+, OH" and C 6 H 5 0- ? What is the pH ofthe solution ? [Ka (phenol) =1.3x10" 10 ] Q.6.6 A weak base (50,0mL) was titrated with 0.1 M HCl. The pH ofthe solution after the addition of 10.0 m L and 25.0 mL were found to be 9.84 and 9.24, respectively. Calculate Kb of the base and pH at the equivalence point. Q.6.7 A weak acid (50.0mL) was titrated with 0.1 M NaOH. The pH values when 10.0 mL and 25.0 mL of base have been added are found to be 4.16 and 4.76, respectively. Calculate Ka of the acid and pH at the equivalence point. Q.6.8 CH3COOH (50 ml, 0.1 M) is titrated against 0.1 M NaOH solution. Calculate the pH at the addition of 0 ml, 10 ml 20 ml, 25 ml, 40 ml, 50 mi of NaOH. K a of CH3COOH is 2 * 10~5. H 3 P0 4 + OH- is 1.4 x 10"12 What is the value of ionization constant for the H 3 P0 4 + H 2 0 Q.ll Given the equilibrium constants HgCl+ + CI" ^ HgCl2 ; Kj = 3 x 106 HgCl~ + CI" ^ HgCl3; K2 = 8.9 The equilibrium constant for the dispropotionation equilibrium. 2HgCl2 ^ HgCl+ + HgClf is

>• H2P04~ + H 3 0 + ?

Q.12 Under which set of conditions is the ionic product of water, K^, constant at a given temperature in aqueous system? Q. 13 If the salts M2X, QY2 and PZ3 have same solubilities (« ^

' - 1.0 x , 0 - or

_ 1.0x10 [S2-]J = 5 = 2.5 x 10-15. 4x10

10" M Q.18 Q.20 No it will be >7 Q.19 (a) 0.0175%, (b) 4.757