3. Describe in detai the Marsh test (second test). if the test tube interior turns dark back after testing (Marsh test)what does it indicate? What is the positive result for Arsenic in the Marsh lest?

The Marsh test is a qualitative analysis procedure used to detect the presence of arsenic in a sample. It involves the following steps:<br /><br />1. Preparation of the sample: The sample is first treated with concentrated hydrochloric acid (HCl) to dissolve any arsenic-containing compounds present in the sample.<br /><br />2. Addition of ammonium iron(II) sulfate: Ammonium iron(II) sulfate is added to the treated sample. This reagent reacts with arsenic to form a black precipitate of iron(III) arsenide.<br /><br />3. Heating: The mixture is then heated gently to facilitate the formation of the black precipitate.<br /><br />If the test tube interior turns dark brown or black after performing the Marsh test, it indicates the presence of arsenic in the sample. This is because the reaction between arsenic and ammonium iron(II) sulfate produces a black precipitate of iron(III) arsenide.<br /><br />The positive result for arsenic in the Marsh test is indicated by the formation of a black precipitate in the test tube. This black precipitate is the iron(III) arsenide formed from the reaction between arsenic and ammonium iron(II) sulfate.