Acid + Metal

[encipher]

Hi,

 

Why do different metals react in odd ways with different acids, example:

 

Zn + HNO3 ---> Zn(NO3)2 + NO2 + H2O

 

Zn + H2SO4 ==> ZnSO4 + H2

 

Zn + HCl ----> ZnCl2 + H2

 

Why does HNO3 give off NO2 gas when reacting with zinc instead of all the NO3- anions going towards making the salt?

 

Now looking at another reaction:

 

Cu + H2SO4 ==> CuSO4 + SO2 + H2O

 

In this reaction Sulfur Dioxide is formed. What's the reason behind this? Again why doesnt all of the SO4 go towards making a salt?

 

Thanks

 

I

[Psycho]

I believe it is to do with the oxidation states of the metals and compounds, it also depends if the products are soluble in water.

[jdurg]

Hi' date='

 

Why do different metals react in odd ways with different acids, example:

 

Zn + HNO3 ---> Zn(NO3)2 + NO2 + H2O

 

Zn + H2SO4 ==> ZnSO4 + H2

 

Zn + HCl ----> ZnCl2 + H2

 

Why does HNO3 give off NO2 gas when reacting with zinc instead of all the NO3- anions going towards making the salt?

 

Now looking at another reaction:

 

Cu + H2SO4 ==> CuSO4 + SO2 + H2O

 

In this reaction Sulfur Dioxide is formed. What's the reason behind this? Again why doesnt all of the SO4 go towards making a salt?

 

Thanks

 

I[/quote']

 

It all has to do with the oxidative properties of the acid. HNO3 is the weakest of the 'strong' acids. As an acid, it isn't all that spectacular. However, HNO3 is a very strong oxidizer. When a metal is added to a solution of HNO3, the HNO3/NO3- is much more favorable to oxidize the metal than the H+ ions are. The result of this is the formation of NO2 gas and water. The remaining NO3- ions in solution balance the charge of the Zn+2 ions in there hence why you get some Zn(NO3)2.

 

HCl, while being a strong acid, is an incredibly poor oxidizer. Therefore, when a metal is placed in a solution of HCl the H+ ion is doing all the oxidation of the metal and the resulting product is H2 gas and a metal chloride.

 

Copper and H2SO4 is a neat little "oddity". Copper metal is not able to be oxidized by hydrogen ions alone. Therefore, in order for it to dissolve in an acid the acid itself must be a fairly potent oxidizing agent. Nitric acid of virtually any concentration is able to dissolve copper because of its strong oxidative properties. Hydrohalic acids (HCl, HBr, HI) cannot dissolve copper because the H+ ion is not a strong enough oxidizer and the halide ions are very poor oxidizers. H2SO4, when dilute, will not dissolve copper to any appreciable extent because the SO4(-2) ion isn't the best of oxidizers, and in a dilute solution not a whole lot of it exists because HSO4- doesn't ionize to any appreciable extent. When you have a concentrated solution and add some heat, however, then the oxidative properties of sulfuric acid are able to oxidize the copper metal. If the Cu is being oxidized, then the sulfuric acid must be reduced and that is why SO2 forms.