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Concentrated hydchloric acid was titrated against a primary standard of sodium...

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nerdygirl-1996 | Student, Undergraduate | (Level 1) Honors

Posted July 22, 2013 at 3:27 AM via web

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Concentrated hydchloric acid was titrated against a primary standard of sodium carbonate and the following burette volume results were obtained:




1st Accurate

2nd Accurate

3rd Accurate

4th Accurate

Initial reading  (mL)






Final Reading (mL)






Titration volume (mL)

20-0 = 20

33-13.6= 19.4

19.2-0= 19.2

24.5-3.8= 20.1

33.4-14.1= 19.3

In each titration 20 ml of 500ml, 0.05mol/L sodium carbonate solution was pipetted into a conical flask and methyl orange was added. The hydrochloric acid was initially prepared as 500ml of approximatley 0.1 mol/L solution. The purpose of the experiment was to standardise the hydrochloric . Using the equation for this reaction calculate the number of moles of sodium crabonate used in each titration and the number of moles of hydrochloric acid used in the titration 

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llltkl | College Teacher | (Level 3) Valedictorian

Posted July 22, 2013 at 7:20 AM (Answer #1)

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The number of moles of a reagent in a certain volume of its solution is obtained by multiplying its molarity with the volume in litres.

Thus the number of moles of Na2CO3 (primary standard) used in each titration



When methyl orange is used as indicator in the titration of Na2CO3 vs. HCl, replacement of both the sodium ions in Na2CO3 by H+ is recorded.

The strength of HCl is first determined by plugging in the average titre value in the titration equation, i.e. V_1*N_1=V_2*N_2 (Note that, N-terms indicate the strengths in normality, which is twice the molarity for a diacidic base like Na2CO3, but equal to molarity for a monobasic acid like HCl):

Here, among the accurate titration results, the third accurate is not acceptable because its value is discordant from the rest. So, the accepted average titre value is (19.4+19.2+19.3)/3=19.3 mL.

therefore, the strength of HCl solutionin molarity

=(20*0.05*2)/19.3=0.103627 (M)

Hence the number of moles of HCl used in each titration is as follows:

Obs. Schedule            Titre value      Number of moles of HCl used

----------------------   ------------   ----------------------------------

Rough                           20     20*0.103627*10^(-3)=0.002073

1st Accurate                 19.4   19.4*0.103627*10^(-3)=0.00201

2nd Accurate                19.2   19.2*0.103627*10^(-3)=0.00199

3rd Accurate                20.1    20.1*0.103627*10^(-3)=0.002083

4th Accurate                19.3    19.3*0.103627*10^(-3)=0.002



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