Describe the reactions, if any, of: (a) potassium, sodium and calcium with cold water (b) magnesium with steam (c) magnesium, zinc, iron, copper, silver and gold with dilute hydrochloric acid and explain these reactions in terms of the position of th

Metals – Reactivity Series

The reactivity series is like a ladder that tells us which metals are more eager to give away their electrons. The higher a metal is on the ladder, the more reactive it is.

(a) Potassium, Sodium and Calcium with Cold Water

When these metals touch cold water, they give up electrons to the water molecules, forming hydroxides and releasing hydrogen gas.

MetalReactionObservations
Potassium (K)\$K + 2H2O \rightarrow KOH + H2 \uparrow\$Explosive fireball ⚡️, bright lilac flame.
Sodium (Na)\$Na + 2H2O \rightarrow NaOH + H2 \uparrow\$Flame orange‑red, moderate heat.
Calcium (Ca)\$Ca + 2H2O \rightarrow Ca(OH)2 + H_2 \uparrow\$Slow fizz, no fire.

Why the difference? Potassium is higher on the ladder than sodium, so it reacts faster and more violently. Calcium is lower, so it reacts more gently.

(b) Magnesium with Steam

Magnesium is a mid‑ladder metal. With hot water (steam) it can give up electrons because the high temperature helps.

Reaction:

\$Mg + 2H2O \;(steam) \rightarrow Mg(OH)2 + H_2 \uparrow\$

Observations: A bright white flame and a cloud of white smoke (magnesium hydroxide).

Analogy: Think of magnesium as a “middle‑aged” metal that needs a push (heat) to start dancing with water.

(c) Metals with Dilute Hydrochloric Acid

Only metals higher than hydrogen in the reactivity series will react with dilute HCl.

MetalReactionResult
Magnesium (Mg)\$Mg + 2HCl \rightarrow MgCl2 + H2 \uparrow\$Fizzes, bubbles of H₂.
Zinc (Zn)\$Zn + 2HCl \rightarrow ZnCl2 + H2 \uparrow\$Fizzes, moderate heat.
Iron (Fe)\$Fe + 2HCl \rightarrow FeCl2 + H2 \uparrow\$Slow fizz, needs warm acid.
Copper (Cu)No reaction (Cu is below H in the series).No bubbles.
Silver (Ag)No reaction.No bubbles.
Gold (Au)No reaction.No bubbles.

Why? The reactivity series (from top to bottom): K, Na, Ca, Mg, Al, Zn, Fe, Ni, Sn, Pb, H, Cu, Ag, Au. Metals above H react with acids; those below do not.

Exam Tips

  • Write the balanced equation – check that atoms and charge are balanced.

  • Use the reactivity series to predict the reaction: higher metals give up electrons, lower metals stay put.

  • Remember that heat can help a metal react with water (e.g., Mg with steam).

  • When a metal reacts with HCl, you usually see bubbling of H₂ – a good visual cue.

  • For metals that do not react, write “no reaction” and explain that they are below hydrogen in the series.

Think of the reactivity series as a race track. The top metal (K) is the fastest sprinter, always ready to give away its electron. The bottom metal (Au) is the relaxed marathon runner – it hardly ever gives up its electrons.