Not All Metals React with Water

What students typically write

“All metals react with water to produce hydrogen.” Or: “Copper reacts with water slowly.”

Students watch dramatic demonstrations of sodium or potassium reacting with water and generalise this behaviour to all metals. They assume metals further down the reactivity series react the same way, just more slowly.

Why it is wrong

The reactivity series is a ranking, and the boundary between “reacts with water” and “does not react with water” falls at a specific place.

React with cold water: potassium, sodium, lithium, calcium (and barium, not usually in the IGCSE list). These produce a metal hydroxide and hydrogen gas. Example: 2Na + 2H2O goes to 2NaOH + H2.

React with steam but not cold water: magnesium, aluminium, zinc, iron. These are not reactive enough to react with liquid water at room temperature, but the higher energy provided by steam allows the reaction to proceed. They produce a metal oxide and hydrogen. Example: Mg + H2O(steam) goes to MgO + H2.

Do not react with water or steam: copper, silver, gold, platinum. These metals are below hydrogen in the reactivity series. They simply do not have the reducing power to displace hydrogen from water in any form.

Copper pipes carry water in buildings precisely because copper does not react with water. If it did, the plumbing would dissolve.

What the mark scheme actually wants

A typical question: “Describe the reactions of sodium, magnesium and copper with water.” [4]

Marking points:

1. Sodium reacts vigorously with cold water to produce NaOH and H2 (1 mark)
2. Magnesium does not react with cold water (1 mark)
3. Magnesium reacts with steam to produce MgO and H2 (1 mark)
4. Copper does not react with water or steam (1 mark)

An answer that says “all three react with water” immediately loses marks 2 and 4.

Worked example: wrong vs right

Question: Predict whether zinc reacts with cold water, steam, or neither. Explain your answer. [2]

Wrong answer: “Zinc reacts with cold water because all metals react with water.” This scores 0/2.

Right answer: “Zinc does not react with cold water but reacts with steam (1). Zinc is moderately reactive — above hydrogen in the reactivity series but below the metals that react with cold water (1).” This scores 2/2.

How to avoid this mistake

Learn the reactivity series with the water-reaction boundary marked:

• K, Na, Li, Ca — react with cold water (hydroxide + H2)
• Mg, Al, Zn, Fe — react with steam only (oxide + H2)
• Cu, Ag, Au — no reaction with water or steam

This three-tier division appears in prediction questions every series. If you can place a metal in the correct tier, the prediction follows automatically.

For the complete reactivity series and reaction patterns, see reactivity series and reactions of metals.