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1. 1. pH
2. 2. Ionic product of waterWater undergoes ionization to a very smallextent producing H+ and OH- ions.So there is an equilibrium between these ionsand the un ionized water molecules. H2O H+ + OH-
3. 3. The product of the concentrations of H+and OH- ions in water is called ionicproduct of water, Kw Kw = [H+] [OH-]
4. 4. In pure water [H+] = 10-7 moles per litre at 25oCAnd [OH-] = 10-7 moles per litre at 25oCKw = [H+] [OH-] = 10-7 X 10-7 moles2/liter2
5. 5. In neutral solution, [H+] = [OH-] = 10-7 moles/litreIf [H+] = 10-7, the solution is neutral. In acidic solution, [H+] > [OH-]If [H+] > 10-7, the solution is acidic.In basic solution, [H+] < [OH-]If [H+] < 10-7, the solution is basic.
6. 6. pH ScalepH scale is a method of expressing hydrogen ionconcentration.It is defined as negative logarithm to the base10 of hydrogen ion concentration in moles perlitre. pH = -log10 [H+]
7. 7. pH of pure waterpH of water = -log[H+] = -log 10-7 = -[-7 log 10] = 7Fundamental equations,log Xn = n log X, log X-n = -n log Xlog (XY)= log X + log Ylog (X/Y) = log X-log Ylog 10 = llog 1 = 0
8. 8. pH of an alkaline solution pH of a base < 10-7Suppose if it is 10-8 [H+] = 10-8-log [H+] = -log 10-8 = -(-8) log 10 = 8 log 10 = 8 x1 = 8
9. 9. pH of an acidic solution pH of an acid > 10-7Suppose if it is 10-2 [H+] = 10-2-log [H+] = -log 10-2 = -(-2) log 10 = 2 log 10 = 2 x1 = 2
10. 10. Kw = [H+] [OH-] If [OH-] = 10-3 Kw = [H+] 10-3 10-14 = [H+] 10-3 [H+] = 10-14 = 10-11 10-3-log [H+] = -log 10-11 = -(-11) log 10 = 11 log 10 = 11 x1 = 11
11. 11. Applications/importance of pH value
12. 12. 1. To find out acidic or basic or neutral nature of a medium2. Selection of pH can reduce the rate of corrosion. Solutions with low pH value (acidic Medium) increases the rate of corrosion.3. In the production of potable water, coagulation of impurities by the addition of alum takes place satisfactorily in the slightly acidic pH range.4. Effluents from chemical factories are either acidic or alkaline. If we know the pH of effluents it is very easy to neutralize properly before discharging them into rivers.5. In electroplating pH is one of the factor which affects the character and appearance of the deposit.
13. 13. 6. pH value of the soil is very important in agriculture. If we know the pH of the soil, it will be helpful to select the proper cultivation. It is also important to find out the type of fertilizers to be applied pH of soil in important.7. pH of human gastic juice is between 1 and 3. Increase of pH generally causes vomiting.8. Acidity in water when used for bleaching cotton will do harm to the textiles.9. In food preservation pH is to be known. Because in biological reactions such as digestion of food depends on pH.10. pH of human blood = 7.36 to 7.42, a change in pH by 0.2 units results in death.
14. 14. Important of pH in boilersBoiler metal is corroded by the acidic nature ofwater. In boilers acid is liberated by thehydrolysis of salts of calcium and magnesium athigh temperature. CaCl2 + 2 H2O Ca(OH)2 + 2 HCl MgCl2 + 2 H2O Mg(OH)2 + 2 HCl The boiler corrosion may leads to explosion.
15. 15. Buffer Solution
16. 16. A solution whose pH value remains constant evenafter the addition of small amount of acid or base iscalled buffer solution.It is a solution in which H+ ion concentration remainspractically constant.i) A weak acid and its salt with a strong base. Eg: A mixture of acetic acid and sodium acetate.ii) A weak base and its salt with a strong acid. Eg: A mixture of ammonium hydroxide and ammonium chloride.
17. 17. Problems