Some Basic Concepts Of Chemistry Question 241

Question: A solution containing Na2CO3 and NaOH requires 300 ml of 0.1 N HCl using phenolpthalein as an indicator. Methyl orange is then added to the above titrated solution when a further 25 ml of 0.2 N HCl is required. The amount of NaOH present in solution is (NaOH=40,,Na2CO3=106) [CPMT 1992]

Options:

A) 0.6 g

B) 1.0 g

C) 1.5 g

D) 2.0 g

Show Answer

Answer:

Correct Answer: B

Solution:

(I) Phenopthalein indicate partial neutralisation of Na2CO3NaHCO3

Meq. of Na2CO3 + Meq. of NaOH = Meq. of HCl WE×1000+WE×1000=NV

(Suppose Na2CO3=a,gm , NaOH = b gm) a106×1000+b40×1000=300×0.1 …..(1) (II) Methyl orange indicate complete neutralisation HCl HCl N1V1=N2V2 , 25×0.2=0.1 × V2,so,V2=50ml excess
a53×1000+b40×1000=350×0.1 …..(2) From (1) and (2) b =1gm.



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