Reaction of Metals with Water and Steam: Class 10

Quick answer: Reactive metals react with water to give hydrogen gas and either a metal hydroxide (with liquid water) or a metal oxide (with steam). Potassium and sodium react violently with cold water; calcium reacts less violently and floats; magnesium reacts only with hot water and also floats; aluminium, iron and zinc react only with steam; and lead, copper, silver and gold do not react with water at all.

The general pattern

The more reactive the metal, the milder the conditions it needs. This follows the reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Ag > Au.

Potassium and sodium: violent reaction with cold water

$\mathrm{2K(s) + 2H_2O(l) \rightarrow 2KOH(aq) + H_2(g)} + \text{heat}$

$\mathrm{2Na(s) + 2H_2O(l) \rightarrow 2NaOH(aq) + H_2(g)} + \text{heat}$

The reaction is so exothermic that the hydrogen produced catches fire immediately.

Because they react so strongly with air and water, sodium and potassium are stored under kerosene.

Calcium: less violent, and calcium floats

$\mathrm{Ca(s) + 2H_2O(l) \rightarrow Ca(OH)_2(aq) + H_2(g)}$

The heat given out is not enough for the hydrogen to catch fire.

Why does calcium float? Bubbles of hydrogen gas stick to the surface of the calcium, and they carry it up to the surface of the water.

Magnesium: reacts with hot water, and floats

Magnesium does not react with cold water. With hot water it gives magnesium hydroxide and hydrogen:

$\mathrm{Mg(s) + 2H_2O(l) \rightarrow Mg(OH)_2(aq) + H_2(g)}$

Magnesium also starts floating, again because hydrogen bubbles stick to its surface.

Aluminium, iron and zinc: react only with steam

These metals react with neither cold nor hot water, but they react with steam to form the metal oxide and hydrogen:

$\mathrm{2Al(s) + 3H_2O(g) \rightarrow Al_2O_3(s) + 3H_2(g)}$

$\mathrm{3Fe(s) + 4H_2O(g) \rightarrow Fe_3O_4(s) + 4H_2(g)}$

Iron forms $\mathrm{Fe_3O_4}$ (iron(II, III) oxide), not $\mathrm{Fe_2O_3}$.

In the laboratory, steam from boiling water is passed over the heated metal, and the hydrogen given off can be collected over water.

Metals that do not react with water

Lead, copper, silver and gold do not react with water at all, even with steam. This is why copper is used for water pipes and why gold and silver keep their shine.

Summary table

Exam tips

• Learn the order K, Na, Ca, Mg, Al, Zn, Fe, Pb, Cu, Ag, Au: it tells you which conditions each metal needs.
• Write state symbols, especially (g) for steam, so the examiner sees you know it is water vapour.
• To explain floating, mention that hydrogen bubbles stick to the metal surface.

Common mistakes

• Writing a hydroxide for the reaction with steam. Steam gives an oxide.
• Writing $\mathrm{Fe_2O_3}$ instead of $\mathrm{Fe_3O_4}$ for iron and steam.
• Saying magnesium reacts with cold water. It needs hot water.
• Forgetting to balance the equations: for example, aluminium and steam need 2, 3, 1, 3.

Frequently Asked Questions

Why does calcium float when it reacts with water?

Bubbles of hydrogen gas formed in the reaction stick to the surface of the calcium, so it floats.

Why is sodium kept in kerosene?

Sodium reacts vigorously with oxygen and with moisture in the air, and can catch fire, so it is stored under kerosene.

What is formed when iron reacts with steam?

Iron(II, III) oxide, Fe₃O₄, and hydrogen gas: 3Fe + 4H₂O → Fe₃O₄ + 4H₂.

Which metals do not react with water at all?

Lead, copper, silver and gold.

Why do metals form oxides with steam but hydroxides with water?

The reaction with steam happens at a high temperature, where metal hydroxides break down into oxides, so the oxide is the product. With liquid water at lower temperature, the hydroxide forms.