Chemical Properties of Metals

Reaction with oxygen. Nearly every metal burns in or slowly combines with oxygen to form a metal oxide. Most metal oxides are basic — soluble ones turn red litmus blue, and all of them react with acids to give a salt and water. Two CBSE-named oxides break that pattern: $\text{Al}_2\text{O}_3$ (aluminium oxide) and ZnO (zinc oxide) are amphoteric, reacting with both acids and bases.

Reaction with water. Reactivity spreads metals along a graded scale. Sodium and potassium attack cold water so violently that the heat released ignites the hydrogen gas on the spot. Calcium reacts with cold water too, but gently — bubbles rise, no fire. Magnesium needs hot water to respond at a useful rate. Iron reacts only with steam. Metals such as gold and silver do not react with water under any ordinary condition.

where: the state symbols record that sodium is solid, water is liquid, the hydroxide forms in aqueous solution, and hydrogen escapes as a gas — every equation in this chapter must carry these four labels to be considered complete.

Reaction with dilute acids. A metal above hydrogen in reactivity displaces it from a dilute acid, producing a salt and releasing hydrogen gas:

The gas is confirmed with the standard test: bring a burning splint near the mouth of the test tube, and the hydrogen burns with a characteristic "pop." Metals less reactive than hydrogen — copper is the standard CBSE example — do not react with dilute acids at all, no matter how long you wait.

Reaction with metal salt solutions (displacement). A more reactive metal, placed in the salt solution of a less reactive one, pushes the less reactive metal out and takes its place in the compound:

This only proceeds in the direction "more reactive displaces less reactive" — never the reverse. The full ordering of metals by this ability is the reactivity series, built and used in its own article, but every displacement question in this chapter is really asking you to apply it.

Chemical reactivity of a metal comes down to one property: how easily its atoms give up electrons to form positive ions. A metal high on this scale — sodium, potassium, calcium — sheds electrons so readily that even the weak pull of water molecules is enough to trigger a fast reaction, releasing hydrogen and enough heat to ignite it for the most reactive pair. As you move down the scale, the atoms hold their outer electrons a little more tightly, so you need a stronger nudge: hot water instead of cold for magnesium, then steam (higher temperature still) for iron, and finally, for gold and silver, no ordinary aqueous condition works at all because their electrons are held too firmly to be pulled off by water. The same electron-losing tendency explains acids and displacement together. Dilute acids supply hydrogen ions, $\text{H}^+$, that need electrons to become hydrogen gas; only a metal willing to donate electrons more readily than hydrogen itself can complete that exchange, which is why copper — less reactive than hydrogen — is inert to dilute acids while zinc is not. Displacement is the identical idea applied metal-to-metal: iron, being more willing to lose electrons than copper, transfers electrons to the $\text{Cu}^{2+}$ ions already dissolved in solution, turning them into solid copper while iron itself dissolves as $\text{Fe}^{2+}$. A less reactive metal simply cannot pull electrons away from a more reactive one's ion, so the reverse reaction never happens — this one-way rule is exactly what the reactivity series is built to rank and predict.

Question: A strip of zinc metal is dropped into a test tube of dilute hydrochloric acid, and a separate iron nail is left standing in blue copper sulphate solution. For each, predict the outcome, write the balanced equation with state symbols, and name the type of reaction.

Step 1 — Zinc and dilute HCl: predict the reaction type. Zinc sits well above hydrogen in reactivity, so it will displace hydrogen gas from the dilute acid, forming a salt.

Step 2 — Zinc and dilute HCl: build and balance the equation. The skeleton is $\text{Zn} + \text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2$. Since zinc chloride is $\text{ZnCl}_2$, two chlorine atoms are needed on the left, so two HCl molecules are required:

Observations: bubbles of a colourless gas form on the zinc surface, the tube warms slightly (the reaction is exothermic), and a burning splint held at the mouth of the tube produces a "pop," confirming hydrogen.

Step 3 — Iron nail in copper sulphate: identify what is happening. The fading of the blue colour signals that copper sulphate is being converted to a paler iron(II) sulphate, and the reddish-brown coating forming on the nail is metallic copper being deposited out of solution.

Step 4 — Iron nail in copper sulphate: write the equation and name the reaction.

This is a displacement reaction: iron, being more reactive than copper, pushes copper out of its salt solution. The pale green colour of $\text{FeSO}_4(aq)$ accounts for the fading blue, and the reddish-brown solid matches metallic copper exactly.

Answer: Zinc gives $\text{ZnCl}_2(aq) + \text{H}_2(g)$ with the "pop" test confirming hydrogen (a metal + dilute acid reaction); the iron nail gives $\text{FeSO}_4(aq) + \text{Cu}(s)$, a displacement reaction possible only because iron is more reactive than copper.

Competitive stretch

If a strip of copper were dropped into the same zinc chloride solution left over from Step 2, nothing would happen — copper is less reactive than zinc, so it cannot displace zinc from $\text{ZnCl}_2(aq)$. This "no reaction" outcome is exactly as testable as a positive one: examiners often ask you to identify when a displacement will not occur, which requires knowing the relative order, not just the two named metals in front of you.

• Writing metal-acid or displacement equations without state symbols, or without checking that atom counts balance on both sides.
• Treating all metal oxides as purely basic — $\text{Al}_2\text{O}_3$ and ZnO are amphoteric and react with both acids and bases; naming any other metal oxide as amphoteric is a common overreach.
• Flattening the water-reactivity gradient into a single "metals react with water" statement instead of the correct spread: cold water (vigorous, for Na/K) to cold water (gentle, for Ca) to hot water (Mg) to steam (Fe) to no reaction (Au, Ag).
• Predicting a displacement reaction without checking relative reactivity first — a less reactive metal can never displace a more reactive one out of its salt solution, regardless of concentration or time given.

Ask the tutor: Want a quick round of "will these two metals react" questions covering oxygen, water, acids, and displacement together? Ask your AI tutor to quiz you.