A student took a half-filled test tube with dilute hydrochloric acid and a few drops of phenolphthalein in the solution. As he put a few drops of sodium hydroxide into the solution, it turns to pink. again he put a few extra drops of Hydrochloric acid the colour disappears. What caused the colour to disappear from the solution?
Answers
Answer:
Neutralisation or acidification.
Explanation:
Sodium Hydroxide is a base. That's why the phenolphthalein turned pink. When he put Hydrochloric acid, the colour disappears because either he put more Hydrochloric acid than he put Sodium Hydroxide, or he put the same amount and the solution turned to water and then the solution returned to its basic colour (transparent). When an acid is put in phenolphthalein, there is NO COLOUR CHANGE. that might be the reason, or it might be that when he put the same amount of each solution, it might have neutralised in a process called neutralisation, where if an acid and base are mixed together in the same amount, it turns to water (with byproducts such as Carbon Dioxide and heat). It is one of these reasons why the solution turned transparent.
P.S
For futher confirmation, ask the student who performed the experiment :)
Answer:
Neutralisation reaction of Hydrochloric acid and sodium hydroxide.
Explanation:
Titration of dilute hydrochloric acid with sodium hydroxide is given in the question. Here, Phenolphthalein acts as an indicator. In acidic and neutral medium, Phenolphthalein is colourless, while in basic medium it turns pink. As Sodium hydroxide is added, pH of the solution increases to basic pH, hence the pink colour. As more sodium hydroxide is added, neutralisation reaction takes place as follows, hence colour disappears corresponding to neutral medium.
HCl + NaOH ⇄ NaCl + H2O
Hope that helps!