Sublimation

Read the following passage and answer the questions from 31 to 35: During the interactions with a group of standard VI students, Dr. Sarvesh demonstrated various experiments involving physical changes viz. Vapourisation/Evaporation (liquid to gas), Melting (solid to liquid), Sublimation (solid to gas) and Chemical changes viz. Neutralization (reaction between acid and alkali), Precipitation (reaction between ammonium chloride/potassium chloride and silver nitrate). This group enjoyed the session and demanded little more information regarding detection of cations and anions in the given solution. With this demand, Dr. Sarvesh designed three experiments (one by observing the changes in the colours of the test papers and another, just observing the change) to detect the presence of ammonium radical in the given salts. Dr. Sarvesh dissolved a small amount (approximately 0.100 g) of each, solid ammonium chloride and solid potassium chloride separately in 2.0 cm of de-ionised water, in two different test tubes labeled '1' and '2' respectively. Two drops of each of the above solutions were separately taken in three different dry test tubes forming two different sets; one set kept on the extreme left and another on the extreme right. The three test tubes, in each of the two sets, were gently heated on adding six drops of 2 N sodium hydroxide (alkali) to each and the evolved gases were carefully brought in contact, separately, with a moist red litmus paper, a moist turmeric paper and a glass rod dipped in dilute hydrochloric acid. Above the test tubes on the left hand side, in the first case, the paper turned blue (this was exactly opposite to acidic gases which turn moist blue litmus red), in the second case the paper turned brown and in the last case dense white fumes of ammonium chloride were observed. No such changes were observed in the colours of both the papers nor dense white fumes above the test tube on the right. Dr. Sarvesh explained that during the reactions between the reagents gaseous ammonia is liberated which is alkaline in nature and inferred that the solution in the left hand side test tubes contains ammonium radical while that in the right hand side test tube does not. Dr. Sarvesh then asked students to perform the test. In the first experiment, Ms. Riya, in addition to the earlier observations, found red litmus turning blue for the test tube on the right while Mr. Ravi, did not get the desired colour change of the turmeric paper on the left hand side test tube. Dr. Sarvesh explained to the students the proper way to perform the tests. Following the instructions from Dr. Sarvesh, when the students correctly performed the tests, they got the desired results.