A special acid
Metals and nitric acid.
No bubbles of hydrogen
Most metals give hydrogen gas with dilute acids. But with nitric acid, HNO₃, something else happens.
What is different about nitric acid?
What this lesson covers
The idea
Hydrogen gas is not evolved when a metal reacts with nitric acid, because HNO3, a strong oxidising agent, oxidises the H2 to water and is reduced to nitrogen oxides; magnesium and manganese give H2 with very dilute HNO3.
No bubbles of hydrogen
Most metals give hydrogen gas with dilute acids. But with nitric acid, HNO₃, something else happens.
What is different about nitric acid?
- Hydrogen gas is not evolved
- It gives more hydrogen than other acids
- It does not react with any metal
Why no hydrogen
Press Next step.
An oxidising acid
Nitric acid is a strong oxidising agent. When a metal reacts with it, the hydrogen that forms is oxidised to water, and the acid is reduced to nitrogen oxides. So hydrogen gas is not evolved. Magnesium and manganese are the exceptions with very dilute HNO₃.
Hydrogen gas is not evolved when a metal reacts with nitric acid, because HNO₃, a strong oxidising agent, oxidises the H₂ to water and is reduced to nitrogen oxides; magnesium and manganese give H₂ with very dilute HNO₃.
Notes
No hydrogen with nitric acid: it is a strong oxidising agent (H₂ becomes water, HNO₃ becomes nitrogen oxides); Mg and Mn give H₂ with very dilute HNO₃.
Check yourself
Hydrogen gas is not evolved with nitric acid because HNO₃ is ...
The hydrogen produced is oxidised by HNO₃ to ...
Nitric acid itself gets reduced to ...
Which two metals give H₂ with very dilute HNO₃?
- a weak acid. The book says HNO₃ is a strong oxidising agent, which oxidises the hydrogen.
- a base. Nitric acid is an acid; the book gives its strong oxidising nature as the reason.
- a strong oxidising agent — correct. Yes!
- water — correct. Yes!
- oxygen. The book says the H₂ is oxidised to water.
- nitrogen oxide. The nitrogen oxides are what the acid itself is reduced to.
- hydrogen. Hydrogen is not evolved; the acid is reduced to nitrogen oxides.
- nitrogen oxides such as N₂O, NO and NO₂ — correct. Yes!
- sulphur dioxide. Nitric acid contains no sulphur; it is reduced to nitrogen oxides.
- Copper and silver. The book names magnesium and manganese as giving H₂ with very dilute nitric acid.
- Zinc and iron. The book names magnesium and manganese as giving H₂ with very dilute nitric acid.
- Magnesium and manganese — correct. Yes!