Question

What colour change does phenolphthalein undergo in nitric acid? What occurs when nitric acid is added to the water? What colour is the universal indicator in nitric acid? What reaction does nitric acid undergo with sodium carbonate?

Answer 1

Phenolphthalein is a compound with the chemical formula $\;{C_{20}}{H_{14}}{O_4}\;$ . Phenolphthalein is generally used as an indicator for acid-base titration. For this application, it turns colorless in acidic solutions and pink in alkaline solutions. It belongs to a class of dyes called phthalocyanine dyes. We will answer the following questions in detail in the solution.

Complete Step By Step Answer:
We know that phenolphthalein is a compound with the chemical formula $\;{C_{20}}{H_{14}}{O_4}\;$ . Phenolphthalein is generally used as an indicator for acid-base titration. It belongs to a class of dyes called phthalocyanine dyes. It is also used in conjunction with methyl red, bromothymol blue, and thymol blue as a component of general indicators. It turns colorless in acidic solution and pink in alkaline solution.
Therefore, nitric acid is a very strong acid. Under strong acid conditions, phenolphthalein is orange.
When nitric acid is added to water, many hydronium ions are formed and the reaction is exothermic in nature. This reaction causes nitric acid to dilute.
When we add a universal indicator to nitric acid, it appears red because nitric acid is acidic in nature.
The reaction of nitric acid and sodium carbonate is as follows:
$HN{O_3}(aq) + NaHC{O_3} \to NaN{O_3}(aq) + C{O_2}(g) \uparrow + {H_2}O(l)$
In this reaction, carbon dioxide is released with vigorous bubbling.

Note:
When the acid dissolves in water, we will obtain an acid solution. When a base dissolves in water, it is a base and forms an alkaline solution. If the solution is neither acidic nor alkaline, it is neutral. Indicator is a chemical substance which changes color when added to an acidic or alkaline solution. Litmus, phenolphthalein, and methyl orange are commonly used indicators in laboratories.