Question

Circles the compounds that are insoluble Pb(NO_3)_2 Na_2S LiBr MgSO_4 BaSO_4 Why was it necessary to clean the wire with acid between flame tests? Fireworks get their color from the compounds that are packed in them. What two elements would be needed to make an orange explosion at a firework display?

Answer 1

1. Out of the given substances, BaSo4 is insoluble in water. Rest of the compound are soluble in water.

Pb(NO3)2- nitrate have good solubility

Na2S and LiBr- boh have cation belonging to alkali metal. so they are soluble

MgSO4- soluble

2. Flame test are used to determine the unknown metal based on the characteristics colour given by the flame. This technique uses a metal wire make a loop, dip the solution in powder or solution and then place in the hottest portion of the flame. The resulting colour is observed which tells about the metal present.

Wire is cleaned with dilHCl and then with distill water. If it is cleaned, then there is burst of colour formed then identification of indiviudal metal become difficult.