A. (33) In a titration to determine the Alkalinity using 200 ml I sample water a

Question

A. (33) In a titration to determine the Alkalinity using 200 ml I sample water and titrating with 0.02 N H2S04 the following species were identified. OH 7 mg/L, as calcium carbonate HCO3-= 100 mg/L, as calcium carbonate CO32-= 50 mg/L, as calcium carbonate Answer the following: rst 1. How-mamy-millititers of aeid-were-tised-in-the first-pert-ofthe titre How-thany additional nilliliters ofteid-was-required-to feaehthefinatend-point ofpH 4.52 What was the initial pH of the sample? 2. 3. ONly aNS uwer 3

Explanation / Answer

Concentration of OH- as CaCO3 = 7mg/L = 0.0007g/L

Molar mass of OH- = 17.01g/mol

Molar mass of CaCO3 = 100.09g/mol

CaCO3 to OH- conversion factor = 17.01/100.09 = 0.16995

Mass of OH- = 0.0007g × 0.16995=0.0001190g

No of mole of OH- = 0.0001190g/17.01g/mol = 7.00 ×10^-6

[ OH- ] = 7.00×10^-6M

pOH = 5.15

pH + pOH = 14

pH = 14 - 5.15

= 8.85

  

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