Question

Assertion In the titration of $\;N{a_2}C{O_3}$ with HCl using methyl orange indicator, the volume of acid required is twice that of the acid required using phenolphthalein as an indicator.
Reason Two moles of HCl are required for the complete neutralization of one mole of $\;N{a_2}C{O_3}$ .
A. Assertion is correct but Reason is wrong
B. Assertion is wrong but Reason is correct
C. Both Assertion and Reason are correct and Reason is the correct explanation of Assertion
D. Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion

Answer 1

In chemistry indicators are chemical compounds that indicate the presence or absence of another compound by a sign of visual change like a change of color of the solution. Such as for acidic and basic solutions. There are some examples of indicators such as methyl blue, phenolphthalein, etc.

Complete step by step answer:
In the case of methyl orange, the volume of the acid required at the equivalence point is twice of the volume required than phenolphthalein. This is because phenolphthalein is a weak organic acid. It can change the color at a very basic basic solution. when $\;N{a_2}C{O_3}$ converts into $\;NaHC{O_3}$ phenolphthalein shows color.
But in the case of methyl orange, it shows color in a weakly acidic solution. Now in medium all bases will be neutralized by acid. so, the volume of acid required doubled in comparison to phenolphthalein.
So, the assertion and reason are correct. But the reason is not the correct explanation of the assertion.

Therefore, the correct option is D.

Additional information:

A universal indicator is a pH indicator of a solution of several compounds. This solution of universal indicator exhibits several color changes from the range of 1-14 in the pH scale. This pH indicator indicates the acidity or basicity of the solution.
According to the pH scale if any solution is with a lower pH value (less than 7) is acidic in nature, and if the pH of the solution is higher (greater than 7) than the solution is basic. For pure water, the pH of the solution is 7.
There are some example of indicators with the pH range as follows

Phenolphthalein	8.2-10
Bromothymol Blue	6.0-8.4
Methyl red	4.2-6.2
Phenol red	6.8-8.4

Now when the color of the solution changes to red then the dilution is acidic. And when the color is blue it is called a basic solution.
Therefore, when a student adds a few drops of the universal indicator to a solution of dilute hydrochloric acid. The color of the solution changes from colorless to Red.

Note: In chemistry, pH is a scale to measure the acidity or basicity of a solution. It is can be calculated by the formula $pH = - \log {\left[ H \right]^ + }$ , where ${\left[ H \right]^ + }$ is the molar concentration of hydrogen ion present in the solution. Molar concentration is also called molarity means the number of moles of a particular solute in a solvent per liter volume of solution.