REACTIONS OF THE GROUP 2 ELEMENTS WITH COMMON ACIDS

This page looks at the reactions of the Group 2 elements - beryllium, magnesium, calcium, strontium and barium - with common acids.

Reactions with dilute hydrochloric acid

All the metals react with dilute hydrochloric acid to give bubbles of hydrogen and a colourless solution of the metal chloride.

X  +  2HCl    XCl₂  +  H₂

As you might expect for elements in this part of the Periodic Table, the reactions get more vigorous as you go down the Group.

Reactions with dilute sulphuric acid

These are more complicated, because of the formation of insoluble sulphates.

Beryllium and magnesium

These are just like the reactions with dilute hydrochloric acid, and you have probably been familiar with the reaction between magnesium and dilute sulphuric acid almost since you started doing chemistry. Bubbles of hydrogen are formed, together with colourless solutions of beryllium or magnesium sulphate.

For example:

Mg  +  H₂SO₄    MgSO₄  +  H₂

Calcium, strontium and barium

Calcium sulphate is sparingly soluble, and you can think of strontium and barium sulphates as being insoluble. That means that you will get a layer of insoluble sulphate on all of these which will slow down the reaction or stop it entirely.

In the calcium case, you will get some hydrogen produced together with a white precipitate of calcium sulphate.

Reactions with nitric acid

These are more complicated. When most metals react with most acids, what they are actually doing is reducing hydrogen ions to hydrogen gas by adding electrons to the hydrogen ions. The metal is, of course, oxidised to positive metal ions because it loses electrons.

But nitrate ions are also easily reduced to products like nitrogen monoxide and nitrogen dioxide.

So metals reacting with nitric acid tend to give oxides of nitrogen rather than hydrogen. If the acid is relatively dilute, you tend to get nitrogen monoxide, although this immediately reacts with oxygen in the air to make brown nitrogen dioxide.

Concentrated nitric acid gives nitrogen dioxide.

Beryllium

There is a lot of disagreement amongst various sources about whether or not beryllium reacts with nitric acid. Beryllium has a strong oxide layer (rather like the more familiar aluminium) which slows reactions down until it has been removed.

Some sources say that beryllium doesn't react with nitric acid. On the other hand, it is easy to find practical details for making beryllium nitrate by reacting beryllium powder with nitric acid. One source uses semi-concentrated nitric acid, and says that the gas evolved is nitrogen monoxide. That is what you would expect.

What seems to be happening is that whether it reacts or not depends on the source of the beryllium (how it was manufactured) - perhaps changing small amounts of impurities in the metal which affect the reaction.

This is all so uncertain that it seems hard to see how a question could be asked about it in an exam.

The other Group 2 metals

These will produce hydrogen from nitric acid provided the acid is very dilute, but even so, it will be contaminated with nitrogen oxides. Colourless solutions of the metal nitrates will be formed.

Taking magnesium as an example, if the solution is very dilute:

Mg  +  2HNO₃    Mg(NO₃)₂  +  H₂

At moderate concentrations (and even with very dilute acid, this will happen to some extent):

3Mg  +  8HNO₃    3Mg(NO₃)₂  +  2NO  +  4H₂O

And with concentrated acid:

Mg  +  4HNO₃    Mg(NO₃)₂  +  2NO₂  +  2H₂O