20 ml of 0.1 M solution of compound Na2CO3.NaHCO3.2H2O is titrated against 0.05 M HCl, x ml of HCl is used  when phenolphthalein is used as an indicator and y ml of HCl is used when methyl...

20 ml of 0.1 M solution of compound Na2CO3.NaHCO3.2H2O is titrated against 0.05 M HCl, x ml of HCl is used  when phenolphthalein

 is used as an indicator and y ml of HCl is used when methyl orange is the indicator in two separate titrations. What is the value of (y-x)?

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llltkl | College Teacher | (Level 3) Valedictorian

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Titration of Na2CO3 using phenolphthalein as indicator involves the reaction: Na2CO3 + HCl = NaHCO3 + NaCl

so 1 Mole Na2CO3 consumes 1 Mole HCl 

or 20 ml 0.1M Na2CO3 soln consumes 40 ml 0.05 M HCl soln. so x = 40.

Titration of Na2CO3 using methyl orange as indicator involves the reactions: Na2CO3 + 2HCl = H2CO3 + 2NaCl

and also   NaHCO3 + HCl = H2CO3 + NaCl

so 1 Mole Na2CO3 consumes 2 Moles of HCl 

and 1 Mole NaHCO3 consumes 1 Mole of HCl 

or 20 ml 0.1M Na2CO3 soln consumes 40x2 ml 0.05 M HCl soln. and 20 ml 0.1M NaHCO3 soln consumes 40 ml 0.05 M HCl soln. (as the compound contains both Na2CO3 and NaHCO3 in equimolar proportion)

Hence y = 40x2+40 = 120

so y - x = 120 - 40 = 80.

 

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