Hydrochloric acid can also be titrated with sodium hydroxide using phenolphthale

Question

Hydrochloric acid can also be titrated with sodium hydroxide using phenolphthalein indicator to determine the endpoint. The Erlenmeyer flask on the left below shows that the only ions present at the start of the titration are H^+(aq) and Cl^-(aq). Indicate the color of the solution at the start. For the second flask, write the chemical formulas for the substances present (other than water) at the endpoint of the titration between hydrochloric acid and sodium hydroxide. Also indicate (by circling) the color of the solution at the endpoint. Before any NaOH(aq) is added, the solution is: pink colorless At the endpoint of the titration, the solution is: pink colorless

Explanation / Answer

When we add phenolphthalene indicator to the first flask containing HCl there is no colour it is colourless.

Since phenolpthalene do not exhibits colour in acidic medium.

The reaction between HCl & NaOH is

HCl (aq) + NaOH (aq) ---> NaCl(aq) + H2O(l)

At the end point all the HCl & NaOH completly reacts to form NaCl which is ionizes in solution as Na+ (aq) & Cl-(aq)

Therefore other than water the solution contains NaCl.

At the end point the colour changes from colourless to pale pink

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