Acid/Metal Reactions

[Vigo]

I have recently been experimenting with different metal reactions with different acids. Some interesting things that I have noticed:

 

1.)Using 3 molar nitric acid and a small mass of iron, I got a reaction which produced a dark brown substance was produced adn the iron was not completely dissolved.

2.)Also using 3 molar nitric acid and about the same mass of copper, the solution turned a light blue.

None of these things happened when I used sulphuric or hydrochloric acid.

 

Feel free to explain why these things occur or comment on them.

[silkworm]

Well, copper in solution is blue. Probably a similar thing is happening in part 1, but I can't think of the color of iron in solution at the moment. However you should have definitely had the same thing happen when using sulfuric acid.

 

Sulfuric and nitcric acids are commonly used to seperate metals from their oxides , and also used to strip metal jackets placed on by electroplating.

[Vigo]

Sorry, I forgot to mention that the iron in 6 molar sulfuric acid (did not test 3 molar) does to brown, but not to the same degree of darkness as 3 molar nitric. The copper did nothing in sulfuric, but I will retest to verify.

[RyanJ]

I have recently been experimenting with different metal reactions with different acids. Some interesting things that I have noticed:

 

1.)Using 3 molar nitric acid and a small mass of iron' date=' I got a reaction which produced a dark brown substance was produced adn the iron was not completely dissolved.

2.)Also using 3 molar nitric acid and about the same mass of copper, the solution turned a light blue.

None of these things happened when I used sulphuric or hydrochloric acid.

 

Feel free to explain why these things occur or comment on them.[/quote']

 

What comments do you want?

 

I'm guessing #1 formed Iron(III) nitrate and for #2 probably Copper(II) nitrate... other than that I'm not shure what you are asking...

 

What do you want to know, if the metals are dissolving in the other acids or are they in colourless solutions - can you be more specific as to what you would like to know?

 

Cheers,

 

Ryan Jones

[Vigo]

I was just wondering why these certain metals only did this in these acids.

 

I retested copper in sulfuric acid, and it did not turn blue like it did with nitric.

 

Another question that I have: How are metals on the reactivity series classified that way? i.e. - Are they determined how reactive they are by how many sloutions they react with, how quickly they react, how much they react, or what?

[budullewraagh]

aha!

 

here's something that genuinely pisses me off because teachers and many books are too stupid to tell the difference.

 

the "reactivity" series you speak of is actually called an "activity" series. the activity series is based on electromotive potentials required to reduce cations of a metal to the ground state. and no, cesium (or francium if your teacher/book gave the impression that it actually exists in any significant quantity in the same place at a given time) is not the most active metal. that would actually be lithium.

 

reactivity is based on rates of reaction- ie, how fast X will react with Y relative to Z reacting with Y when all reactants are in the same conditions in both reactions.

[Vigo]

Ok that clarifies things a bit.

 

http://www.chemos.co.uk/Reactivity.htm - This is the link that I was using for reference. Obviuosly, it labels caesium as the most reactive metal, which budullewraagh said was wrong.

 

What I did in my experiments was measured out 25 ml of acid into a petri dish. Then I cut relatively similar masses of metals (Mg, Cu, Fe, Pb, Al, and Zn) and let them react fully. Then I measured the volume of the acid left. I was just wondering how I would make my own list of metal activity.

[woelen]

With copper you get copper (II) nitrate. The 3M HNO3 is a sufficiently strong oxidizer to oxidize copper metal to copper (II) ions. The same concentration of H2SO4 or HCl is not capable of doing this. Nitric acid reacts as a stronger oxidizer than the other acids, because the nitrate ion also acts as oxidizer. The nitrate ion is coverted to NO and/or NO2 in this redox reaction. In the other acids only the H(+) ion is the oxidizer: 2H(+) + 2e ---> H2

 

Iron also dissolves in sulphuric acid and hydrochloric acid. Here the simple H(+) ion is sufficiently strongly oxidizing to dissolve the metal.

 

When iron is dissolved in HNO3 then again also NO and/or NO2 are formed. These form a deep brown complex with iron (II) ions and formation of this complex causes the brown color. This brown complex is [Fe(NO)(H2O)5](2+). Iron is in the +1 oxidation state in this complex, the NO(+) ligand contains N in the +3 oxidation state. So, with iron and nitric acid the reaction is much more complicated than with other acids. In the other acids you simply get H2 and Fe(2+), where oxygen from the air oxidizes Fe(2+) further to Fe(3+).