Some Basic Concepts Of Chemistry Question 241
Question: A solution containing $ Na _2CO _3 $ 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,,Na _2CO _3=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 $ Na _2CO _3\to NaHCO _3 $
Meq. of $ Na _2CO _3 $ + Meq. of NaOH = Meq. of HCl $ \frac{W}{E}\times 1000+\frac{W}{E}\times 1000=NV $
(Suppose $ Na _2CO _3=a,gm $ , NaOH = b gm) $ \frac{a}{106}\times 1000+\frac{b}{40}\times 1000=300\times 0.1 $ …..(1) (II) Methyl orange indicate complete neutralisation HCl HCl $ N _1V _1=N _2V _2 $ , $ 25\times 0.2=0.1 $ $ \times $ $ V _2,so,{V_2}=50ml $ excess
$ \therefore $ $ \frac{a}{53}\times 1000+\frac{b}{40}\times 1000=350\times 0.1 $ …..(2) From (1) and (2) b =1gm.
