Question

For a given mixture of\[NaHC{{O}_{3}}\]and \[N{{a}_{2}}C{{O}_{3}}\] volume of HCl required is xml with phenolphthalein indicator and further y ml required with methyl orange indicator. Hence, volume for complete reaction of \[NaHC{{O}_{3}}\]is:
A. 2x
B. \[\dfrac{x}{2}\]
C. y
D. (y-x)

Answer 1

Hint: Phenolphthalein is an organic compound which is used as a cathartic. We use phenolphthalein as an indicator in acid base titration. It has the tendency to dissolve alcohols and are slightly soluble in water. the colour of it varies from yellowish white to pale orange. It appears colourless in its liquid form.

Complete step-by-step answer:The methyl orange indicator has the ability to show and indicate the complete neutralization of sodium carbonate and of sodium bicarbonate. But the phenolphthalein tends to show or indicate only the 50% reaction of sodium carbonate and sodium bicarbonate at a stage only.
So let us assume that the required HCl for the reaction of complete neutralization of sodium bicarbonate is = \[{{V}_{1}}\]
Let us assume that the required HCl for the reaction of complete neutralization of sodium carbonate is = \[{{V}_{2}}\]
For the indicator of phenolphthalein which shows 50% reaction for sodium carbonate, the HCl required is = \[\dfrac{{{V}_{2}}}{2}\]=x
For the indicator of methyl orange for further titration the HCl required will be= \[\dfrac{{{V}_{2}}}{2}+{{V}_{1}}\]=y
Now the volume of HCl required for sodium bicarbonate \[{{V}_{1}}\]= (y-x) ml

So the correct answer is option D.

Note:Phenolphthalein is used in Kastle Meyer test.it is considered as a weak acid and the colour of phenolphthalein ion is purple. In the titration is used to determine the end point of the titration. It indicates the end point by forming a pink colour as this compound has the tendency to form pink colour anion on dissolving in water.