There is this question I was asked: how will copper react with nitric acid? I thought, let's answer this question in a blog since there are many aspects to this reaction.
Copper reacts a little differently with dilute and concentrated nitric acid (HNO3). Well, the only difference is really the pH of the product. First let's see what is the difference between dilute and concentrated. Dilute essentially means more water has been added to the solution, and concentrated means there is little to no water present in the solution. Scientifically speaking, in a diluted solution there will be less H+ ions per unit volume, and in a concentrated solution there will be more H+ ions per unit volume.
Before getting into the actual reaction, here is something you should know about nitric acid. HNO3 is a very strong oxidising agent and therefore when metals react with it, hydrogen is not produced. There are exceptions to this of course, only manganese and magnesium produce hydrogen when they react with HNO3. This is because only these two elements are able to displace hydrogen from HNO3.
The reaction of copper with nitric acid according to its equation is this.
4HNO3 + Cu ----> Cu (NO3)2 + 2NO2 + 2H2O
Scientifically, it means 4 moles of HNO3 reacts with 1 mole of Copper to give 1 mole of Copper nitrate, 2 moles of nitrogen-di-oxide and 2 moles of water.
The copper nitrate that is formed is blue in colour like most copper salts. Now, checking the pH of salts formed as a result of copper reacting with dilute acid and concentrated acid.
The Copper nitrate formed by the concentrated acid will be more acidic than the one formed by the dilute acid, because H+ ions are more in concentrated solution.
Usually when metals react with acids, hydrogen gas is produced, here is ideal equation.
Metal + Acid -----> Metal salt + Hydrogen
As mentioned above, HNO3 is a strong oxidising agent and produces hydrogen only when it reacts with Mg and Mn. So, what happens to the hydrogen when HNO3 reacts with other metals? HNO3 oxidises the hydrogen produced, making it water.
Here is a video of the reaction between copper and nitric acid by the Royal Society of Chemistry.
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