Transcript of "Acids and bases dr.surendran prambadath"
Acids and Bases are two classes of chemicalcompounds that display generally oppositecharacteristics.When aqueous solution of an acid and a base arecombines, a neutralization reaction occurs.This reaction is very rapid and generally produceswater and a salt. HCl + NaOH NaCl + H2O
Acids:----a)Turns blue litmus red,b)Has sour taste,c)Conducts electricity,d)Reacted with certain metals to give offhydrogen gas,e)Reacted with carbonates to evolve carbondioxide gas, andf)Reacted with bases to neutralize them.
Bases:----a)Turns red litmus blue,b)Has bitter taste,c)Conducts electricity,d)Has a soapy, slippery touch, ande)Reacted with acids to neutralize them.
Arrhenius Concept of Acids & Basesa) An acid is a substance which gives hydrogen ions, H+ when dissolved in water.b) A base is a substance which gives hydroxyl ions, OH- when dissolved in water.c) Neutralization is the combination of H+ ions from acid and OH- ions from the base forming H2O.
Lewis Concept of Acids & Basesa) An acid is an electron pair acceptor.b) A base is an electron pair donor.c) During neutralization, base donates an electron pair to the acid forming a co-ordinate bond.
Lewis Acids:----- BF3, AlCl3, SnCl4, H+Lewis Bases:----- NH3, H2O, OH-Neutralization:----- H F H FH N: + B F H N B F H F H F
Strong acids: An acid which is completely ionizedin water and thus produces a large number ofhydrogen ions is called a strong acid. “Strong” means “Degree of ionization” HCl aq H+ aq + Cl- aq H2SO4 aq H+ aq + SO42- aq HNO3 aq H+ aq + NO3- aq
Weak acids: An acid which is partially ionized inwater and thus produces a small number ofhydrogen ions is called a weak acid. HCN aq H+ aq + CN- aq H3PO4 aq H+ aq + PO42- aq CH3COOH aq H+ aq + CH3COO- aq
Strong bases: A base which is completely ionizedin water and thus produces a large number ofhydroxide ions is called a strong base. NaOHaq Na+ aq + OH-aq KOH aq K+ aq + OH-aq
Weak bases: A base which is only partially ionizedin water and thus produces a small number ofhydroxide ions is called a weak base. NH4OHaq NH4+ aq + OH-aq Mg(OH)2 aq Mg2+ aq + OH-aq Ca(OH)2 aq Ca2+ aq + OH-aq
Basicity of an acid is the number of replaceable orionisable hydrogen atoms present in a molecule ofthe acid.HCl, HNO3, CH3COOH ……..Basicity = 1Simply……..Monobasic acidsH2SO4, H2CO3 ………Basicity = 2Simply……..Dibasic acidsH3PO4 ………..Basicity = 3Simply……..Tribasic acids
Acidity of the base is the number of replaceableor ionisable hydroxyl groups present in a moleculeof the base.NaOH, KOH ……..Acidity = 1Simply……..Monoacidic basesCa(OH)2, Mg(OH)2, ………Acidity = 2Simply……..Diacidic basesFe(OH)3, Al(OH)3………..Acidity = 3Simply……..Triacidic bases
Consider two reactions………………. HCl + NaOH NaCl + H2OH2SO4 + 2NaOH Na2SO4 + 2H2OExamine the number of H+ needed to reactwith one molecule of base. Get your answer…!
Consider two more reactions………… 2HCl + Ca(OH)2 CaCl2 + 2H2O2HCl + Na2CO3 2NaCl+ CO2 + H2OExamine the number of OH- or +ve ionneeded to react with one molecule of acid. Get your answer…!
Molecular weightEquivalent weight of an acid = Basicity Molecular weightEquivalent weight of a base = Acidity
According to electronic Concept…….Oxidation means Loss of electronsM M+ + e-Reduction means Gain of electronsM + e- M-
During Redox reaction,Oxidation and reduction will take placetogether.An oxidising agent will get reduced andreducing agent will get oxidised.Understand…….oxidising agent……reducing agent……
Oxidation NumberOxidation number or oxidation state isdefined by the total number of electronsthat an atom either gains or loses in orderto form a chemical bond with anotheratom. Make it by heart……..!
Rules for assigning oxidation number1 The algebraic sum of the oxidation numbers of all atoms in a compound is zero.2 Oxidation number of an element in its elementary state is zero.3 Oxidation number of all metals in all compounds is positive.4 Oxidation number of all non-metals in all compounds is negative.5 Oxidation number of hydrogen is +1, but in hydrides it is -1. (NaH, MgH 2)6 Oxidation number of oxygen is -2, but in peroxides it is -1 and in OF 2 it is +2.7 Oxidation number of first group element is is +1 and that of second group element it is +2.8 The oxidation number of the elements in their molecules like H 2, N2, Cl2, Br2, O2 etc is zero.9 The oxidation number of a simple ion is equal to the charge on the ion.
Find the oxidation numbers of S in i) H2SO4 ii) Na2SO4 iii) H2S O N of H = +1, O = -2…….So O N of S = X In H2SO4, 1x2 + X + -2x4 = 2+X-8 = 0 X-6 = 0, ie, X = 6 O N of Na = +1, O = -2…….So O N of S = X In Na2SO4, 1x2 + X + -2x4 = 2+X-8 = 0 X-6 = 0, ie, X = 6 O N of H = +1, …….So O N of S = X In H2S, 1x2 + X = 2+X = 0 ie, X = -2
Salt bridge –Cell KCl in agarConstruction Provides conduction between half-cellsObserve theelectrodes tosee what isoccurring. Cu Zn 1.0 M CuSO4 1.0 M ZnSO4
What about half-cell What about the sign of reactions? the electrodes? + - Why?cathode half-cell anode half-cellCu+2 + 2e- Cu Zn Zn+2 + 2e-Cu Zn electrodedeposits on What erodeselectrode happened at or dissolves Cu each Zn electrode? 1.0 M CuSO4 1.0 M ZnSO4
Definitions: CATHODE REDUCTION occurs at this electrode ANODE OXIDATION occurs at this electrode
Zn Zn+2 + 2e- Anode Cu+2 + 2e- Cu CathodeZinc plate is eaten away and Copper deposits on thecopper plate. Electrons produced at the zinc anode flowthrough the outer circuit to the copper cathode.Electric Current is assumed to flow from copper to zinc,ie, from positive terminal to negative terminal.
Electricity can be produced by connecting two different metals in solutions of their metal ions. e- e-Copper A Zinc Ion/salt bridgeCopper sulphate solution Zinc sulphate solution
The purpose of the “ion bridge” (“salt bridge”) is tocomplete the circuit. e- e-Copper A Zinc Ion/salt bridgeCopper sulphate solution Zinc sulphate solution
Parts of Daniel cell1.Two half cells, namely zinc half cell and copper half cell. In the former is a zinc rod dipped in a ZnSO4 solution and thelatter is a copper rod dipped in a CuSO4 solution. The twometallic rods are called electrodes.2. The two half cells are connected externally by a metallic wireto a galvanometer through a key and internally by a salt bridge.3. The salt bridge is an inverted U-tube containing an arousesolution of an inert salt like KCl, KNO3, NH4NO3 to which someagar-agar or gelatin has been added to convert it into a semi solid,ie gel. The ends of the U-tube are plugged with glass wool.
1.Permits the passage of electric current internally,2.Maintains the electrical neutrality of the solution,3.Prevents intermixing of the solutions,4.It does not take part in cell reaction. Representation of Daniel Cell Zn(s) / Zn2+(aq) // Cu2+(aq)/Cu(s)
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