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Copper reacts with concentrated nitric acid and gives copper(II) nitrate, brown nitrogen dioxide…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Copper reacts with concentrated nitric acid and gives copper(II) nitrate, brown nitrogen dioxide gas and water. The skeleton equation is . Balance it by the oxidation number method.
Need a reminder? The key ideaShow
The total rise in oxidation number equals the total fall: electrons lost equal electrons gained. Match the changes first. Then balance the atoms that did not change, charge, hydrogen and oxygen.
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Oxidation numbers. Copper goes from to , a rise of 2. Nitrogen goes from in to in , a fall of 1.
Step 2. Match. One copper atom loses 2 electrons. Each gains 1. So 2 nitrogen atoms are reduced for each copper atom: .
Step 3. Nitrogen. Two nitrate ions stay in the salt, and two nitrogen atoms go into . So 4 molecules of are needed.
Step 4. Hydrogen and oxygen. Four hydrogen atoms on the left give 2 water molecules. Oxygen: 12 on the left, and on the right.
Answer: . The coefficients asked for are 4, 2 and 2.
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