Hydrogen is evolved by action of cold dilute HNO3 on
Answers
Answer:
Mg and Mn react with cold dil. HNO3 to give H2.
Explanation:
Mg + 2HNO3 = Mg(NO3)2 + H2
Al usually will not react too much because it will be rendered passive immidietly (except if conc. is really low) due to formation of Al2O3 layer on its surface (due to oxidation by HN03)
Fe will react as follows (Will get oxidized to Fe2+ or Fe3+ by HNO3, depending on many factors, primarily conc.)
4Fe(s]+10HNO3(aq]→4Fe(NO3)2(aq]+N2O(g]+5H2O(l]
Fe(s]+6HNO3(aq]→Fe(NO3)3(aq]+NO2(g]+3H2O(l]
Cu will react in a similar way producing Cu2+.
3Cu + 8 HNO3(dilute) → 3Cu(NO3)2 + 2NO + 4H2O
Remember, remember of H2 by reaction of a metal and HNO3 is rare because H2 will be easily oxidized to h2o by the powerful oxidizing agent, HNO3.
The exact reasons behind the reactions actually lie with electrochemistry.
Certain metals like Mg, say, will be oxidized by the hydrogen ions.Mg2+ has a reduction potential of -2.37V, which is less than H+'s reduction potential of 0V. Hence, H2 gas is produced spontaneously.
However, metals like Iron have a reduction potential(+2.87V) greater than 0V. This means that H+ will no longer be able to oxidize these metals. Instead, the NO3−ion will serve as the oxidizing agent.
Remember, when the reduction potential is higher, tendency of metal to undergo reduction is also higher, and vice versa.
Hydrogen is evolved bt the action of cold dil. HNO3 on Mg [Magnesium]