2006-10-28 19:58:49 · 4 answers · asked by teddie8362 2 in Science & Mathematics ➔ Chemistry
The brown colouration comes from NO2 dissolved in the acid, which tends to happen as the acid ages...if you open the bottle slowly sometimes you will see brown fumes emitted.
2006-10-29 03:32:41 · answer #1 · answered by drjaycat 5 · 0⤊ 0⤋
Epihany has the right idea although the brown colouration can also be due to contamination with iron (as conc sulphuric acid is an oxidising agent and will produce brown iron III sulphate) The NO2 mentioned is the cause of the brown colour of concentrated NITRIC acid rather than sulphuric acid. Pure sulphuric acid is colourless.
2006-10-29 19:08:28 · answer #2 · answered by Examiner 3 · 0⤊ 0⤋
Sulphuric acid is actually colorless. It only becomes brown when organic material gets into contact with it. This is a result of the acid destroying the biological material and setting free carbon.
An easy demonstration experiment is adding H2SO4 conc. to sugar granulates. The sugar turns black (carbon).
So brown sulphuric acid is "old" and should not be used for analytical purposes.
2006-10-29 13:27:22 · answer #3 · answered by Epiphany 1 · 0⤊ 0⤋
Different purities of H2SO4 available. Technical grade H2SO4 is impure and often coloured, hence the brown colour.
2006-10-29 04:47:45 · answer #4 · answered by fionabrown78 2 · 0⤊ 0⤋