Final answer:
The white powder is likely bleaching powder, primarily consisting of calcium hypochlorite, used for its bleaching properties in laundries. The preparation involves reacting chlorine gas with slaked lime to produce bleaching powder, calcium chloride, and water.
Step-by-step explanation:
The white amorphous powder that emits a greenish yellow gas with a smell of chlorine and is used to remove the yellowness of white clothes in laundries is most likely bleaching powder. This powder is commonly composed of calcium hypochlorite [Ca(OCl)2]. The preparation of bleaching powder can be represented by the chemical equation:
2Cl2 + 2Ca(OH)2 → Ca(OCl)2 + CaCl2 + 2H2O
In this reaction, chlorine gas reacts with slaked lime, which is calcium hydroxide. This reaction produces bleaching powder (calcium hypochlorite), along with calcium chloride and water as byproducts. The bleaching agent within the powder, when dissolved in water, releases chlorine which helps in whitening clothes.