Conc & Dil Sulphuric Acid differences

Описание: Distinguish between conc. & dilute Sulphuric acid using single reagent.
Acids in conc & dilute behave differently and produces different results. In this video, we'll see the difference and also learn a few interesting facts that are very important for competitive and board exams. Enjoy the video, Thanks!

SUMMARY:

A quicker and easier method is to use pure (solid) potassium iodide or sodium iodide.
When a little iodide salt is heated gently with conc.H2SO4, purple vapours of iodine (I2) will evolve, along with colorless sulphur dioxide (SO2). The contents of the test tube also turn purple-grey.
2KI + H2SO4 = K2SO4 + 2HI
2HI + H2SO4 = SO2 + I2 + 2H2O
The hydrogen iodide (HI) initially formed by double decomposition is readily oxidised to free iodine by excess conc.H2SO4.
Dilute H2SO4 does not produce any visible chemical change with the iodide salt as it is non-oxidising.
In place of an iodide salt, sodium bromide or potassium bromide can also be used. The bromide salt will give off orange-brown vapours of free bromine on heating with conc.H2SO4 by similar reaction.
Both HBr and HI are strong reducing agents and so they are easily oxidised to free bromine and iodine respectively by hot conc.H2SO4.
A chloride salt is of no use here as HCl, a mild reducing agent, is not easily oxidised by hot conc.H2SO4.

Learning Outcomes:
1. Hot conc. H2SO4 is a moderately strong Oxidising Agent while Dilute H2SO4 is a non-oxidising agent. [The difference]
2. Free Hits:
a) Colours-
i) Iodine (I2): purple vapours
ii) Bromine (Br2): Orange-brown
iii) Sulphur Dioxide(SO2): Colourless

b) HBr and HI are strong reducing agents while HCl is a mild reducing reagent.