Question

Marsh test is used for detecting:
A) As
B) Zn
C) Al
D) $C{H_4}$

Answer 1

A highly sensitive test for testing poisonous content in foods, fruits, vegetables etc. It is done as a quality testing and it is done when the reactant reacts with nitric acid in the present of zinc. In this test an oxide is formed which is poisonous in nature, odorless and easily gets into food drinks etc. We can easily trace it with the help of a simple glass apparatus in which if we react to the substance in presence of zinc and then lighted it, it will show black deposits.

Complete answer:
There is a very interesting story behind this test, we all know that every discovery in science comes through an incident. Like if we talk about the Marsh test, the great scientist “John Bodle” was bought arsenic for poisoning his grand-mother. Yes, this test is for arsenic today and is available as a small amount in every edible item sometimes so as to ensure that any food item is free from arsenic oxide or we call it poison many laboratories and industries which manufacture food items perform marsh test.
This test is performed using a simple glass apparatus which is manufactured to detect minute traces of arsenic and also its quantity. If we try to test a bread slice which is already dropped with arsenic. In the sample if we add zinc it will produce arsenic gas. After that we pass hydrogen gas and also ignite the gas mixture it would oxidize the arsenic particles which are present in a bread slice into arsenic oxide. That arsenic is seen in a cold ceramic bowl as silvery-black deposit.
$A{s_2}{O_3}\, + \,6\,Zn\, + \,12\,HN{O_3}\, \to \,2\,As{H_3}\, + \,6\,Zn{(N{O_3})_2}\, + 3\,{H_2}O$

Note: If we have any idea about the radical’s test we can choose from these options which will be correct and then we can easily tick the right option. Arsenic gives a black color precipitate as its oxide. Zinc doesn’t give marsh test nor aluminum. This test is for poisons detection and we know that aluminum is used in food packaging.