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Dr.  Hoda   Bassem   Qasim   / Medicine, / Mcs ./ University of Karbala.

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Preparation of 0.1Nsodium hydroxide and its standardization with standard  HCl  solution

Theory  The hydroxide of sodium and potassium cannot be considered as a primary  materials because they are hydroscopic substances due to their absorption of water   vapour  from atmosphere and formation of carbon dioxide layer thus they present  as impure hydroxides surrounding with H2O and CO2. Therefore, the  standardization of basses in presence of carbonate ion against acid gives imprecise results ;

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It is necessary to obtain a pure  NaOH  or KOH when preparing standard solution.  They are very soluble in water and cheap thus they are used in preparing standard  solutions .

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Procedure   1- Fill the burette with standard  HCl  solution with known normality.  2- Pipette 10 mL of unknown concentration of  NaOH  into conical flask , then add 2 drops of  ph.ph.indicator   solution,apink   colour  is obtained.  3- Titrate with standard  HCl  solution until a  colourless  solution is obtained and record the volume of  HCl  at endpoint.   4- Repeat the above procedure three time until constant readings.   5- Calculate the arithmetic mean of the three reading and calculate the normality of  NaOH .

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V2-V1 Volume of  HCl  (V2)  Volume of  HCl (V1) Volume of  NaOH (mL)  Exp. No. 10 1. 10 2. 10 3.

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Arithmetic mean= Sum of readings/ No. Of readings.   By using dilution law ,calculate the exact normality of HCl  = NaOH   N  HCl   * V  HCl  = N    NaOH * V   NaOH   NHClx (V2-V1)=NNaOHx10

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