Question

Three test tubes X, Y and Z each contain a small amount of water.
- A small amount of$NaCl$is added to test tube X.
- A small amount of$SiC{{l}_{4}}$ is added to test tube Y
- A small amount of$AlC{{l}_{3}}$is added to test tube Z.
After a short time, two drops of universal indicator solution are added to each test tube.
Which observations are made?
1. The indicator added to test tube X stays green
2. The indicator added to test tube Y turns red
3. The indicator added to test tube Z turns red
A) 1,2 and 3 are correct
B) 1 and 2 only are correct
C) 2 and 3 only are correct
D) 1 only is correct

Answer 1

Hint: The answer for this question can be approached on the basis of the concepts of inorganic chemistry laboratory experiment that deals with the reaction of acidic and neutral compounds with that of universal indicator.

Complete step by step answer:
We have come across the universal indicator which is the pH indicator that gives different colours for the different types of solutions that are acidic, basic or neutral solutions.
Based on this, let us now solve the above question which has the three compounds and let us find out which are acidic and which are basic or which neutral solution is.
- pH indicator also called universal indicator changes the colour according to different pH environments, at low pH it appears red and at higher pH, it appears blue or violet which is again dependent on the strength of base or acids.
- Now in the test tube X, $NaCl$ is added. This compound is actually a neutral compound and by adding this to water which is neutral, it remains a neutral solution itself. Thus, the colour stays green which is the colour for neutral solutions.
- In test tube Y, $SiC{{l}_{4}}$ is added to water and this compound is strong acid and thus adding a small amount of water doesn’t much affect its acidity and hence the colour will turn red.
- In test tube Y, $AlC{{l}_{3}}$ is added which is also a strong acid that is , it is a Lewis acid and thus on adding water the acidity is not much affected and therefore the colour turns red which indicates that both the solutions of $AlC{{l}_{3}}$ and $SiC{{l}_{4}}$ are acidic.

Thus, the correct answer is option A) 1,2 and 3 are correct.

Note: Universal indicator that is pH indicator is also available in the form of a $pH$ paper or also it is a solution which is brown in colour that is a mixture of several indicators which can be added to any substance for the determination of $pH$.