A metal cannot react with its own salt solution because displacement reactions require a difference in reactivity between two metals. When you place a metal into a solution of its own salt, the metal and the metal ions in solution are chemically identical same element, same position in the activity series, zero driving force for any reaction. Nothing happens.
That’s the short answer. Now let’s understand exactly why, from the ground up.
A displacement reaction happens when a more reactive metal pushes a less reactive metal out of its salt solution. Think of it like a bouncer at a door only someone stronger gets to take the spot.
Here’s the classic example:
Zn + CuSO₄ → ZnSO₄ + Cu
Zinc is more reactive than copper. So zinc “kicks out” copper from copper sulphate, takes its place in the solution, and copper metal deposits out. You’d actually see the blue colour of copper sulphate fade and a reddish-brown copper deposit form on the zinc strip. That’s chemistry you can see with your own eyes.
The rule is simple: a more reactive metal displaces a less reactive metal from its salt solution.
But here’s where students trip up what if you use the same metal?
The activity series (also called the reactivity series) ranks metals from most reactive to least reactive. It’s your most important tool for predicting whether a displacement reaction will occur.
| Metal | Symbol | Reactivity (High to Low) |
|---|---|---|
| Potassium | K | Highest |
| Sodium | Na | Very High |
| Calcium | Ca | High |
| Magnesium | Mg | High |
| Aluminium | Al | Moderate-High |
| Zinc | Zn | Moderate |
| Iron | Fe | Moderate |
| Lead | Pb | Low-Moderate |
| Hydrogen | H | Reference Point |
| Copper | Cu | Low |
| Silver | Ag | Very Low |
| Gold | Au | Lowest |
A metal can displace any metal that sits below it in this list. Zinc can displace copper (zinc is above copper). Copper cannot displace zinc (copper is below zinc). Iron can displace copper. Magnesium can displace zinc, iron, copper all of them.
Now look at what happens when you ask: can zinc displace zinc? Can copper displace copper?
A metal and its own ion occupy the exact same position in the activity series. There’s no “above” and “below.” There’s no difference. And without a difference, there’s no reaction.
Reactivity in metals comes down to how easily a metal loses electrons. A more reactive metal loses electrons more readily, and that’s what drives displacement.
In a displacement reaction, here’s what actually happens at the ionic level:
This electron transfer only happens because zinc “wants” to lose electrons more than copper does. Zinc has a stronger drive to become an ion.
Now put zinc in zinc sulphate. The zinc metal might release Zn²⁺ ions into solution — but Zn²⁺ ions are already sitting there in solution, and they’re equally likely to deposit back as zinc metal. The forward and backward processes happen at exactly the same rate. There’s no net change. You end up with the same zinc metal and the same zinc sulphate you started with.
Chemistry doesn’t change for the sake of changing.
Let’s use copper and copper sulphate (CuSO₄) as the example.
Copper sulphate dissolves in water to give Cu²⁺ ions and SO₄²⁻ ions floating around in solution. Now you drop in a piece of copper metal.
For a reaction to happen, the copper metal (Cu) would need to release electrons and become Cu²⁺ ions. But the Cu²⁺ ions already in solution are simultaneously sitting there, perfectly ready to absorb electrons and become Cu atoms again.
These two processes Cu losing electrons and Cu²⁺ gaining electrons — happen at exactly the same rate. They cancel each other out. The net result: zero change.
No colour change. No deposit. No reaction. Just a copper strip sitting in blue copper sulphate, looking bored.
This is what chemists mean when they say ΔG = 0 for this reaction. The free energy change is zero. There’s no thermodynamic “reason” for the reaction to proceed in any direction.
You’ve probably studied equilibrium: some reactions don’t go to completion, they reach a balance point where the forward and backward reactions happen at the same rate.
When a metal sits in its own salt solution, you don’t even get a meaningful equilibrium you get a situation where the forward reaction (metal → ion) and reverse reaction (ion → metal) are not just balanced, they’re identical processes happening simultaneously with no preference either way.
The system is already at equilibrium before anything starts. Nothing shifts. Nothing changes.
Here’s where it all comes together. Let’s compare reactions that work versus ones that don’t:
Reactions that DO occur:
Reactions that do NOT occur:
| Metal | Salt | Reacts with Its Own Salt? | Why Not? |
|---|---|---|---|
| Zinc (Zn) | Zinc Sulphate (ZnSO₄) | No | Same reactivity — no displacement possible |
| Copper (Cu) | Copper Sulphate (CuSO₄) | No | Metal and ion are identical; ΔG = 0 |
| Iron (Fe) | Iron Sulphate (FeSO₄) | No | No difference in reactivity to drive reaction |
| Silver (Ag) | Silver Nitrate (AgNO₃) | No | Metal equals its own ion — no net change |
Every case is the same story. Different metals, same reason.
When an exam question asks you to predict whether a reaction happens, follow these steps:
That’s it. This approach handles every variation an exam can throw at you.
Q: What happens when a copper strip is placed in copper sulphate solution?
Answer: No reaction. Copper cannot displace itself from its own salt.
Q: Will zinc react with zinc sulphate? Justify your answer.
Answer: No. Zinc and the zinc ions in solution are the same element. There’s no difference in reactivity, so no displacement can occur.
Q: Which of the following will show a displacement reaction:
(a) Fe in FeSO₄
(b) Fe in CuSO₄
(c) Cu in FeSO₄?
Answer:Only (b).
Iron is more reactive than copper, so iron displaces copper from copper sulphate. In (a), iron can’t displace itself. In (c), copper is less reactive than iron, so no displacement.
A metal can’t react with its own salt solution because displacement reactions depend on a difference in reactivity between two metals. When the metal and the metal ions in solution are the same element, there’s no reactivity difference. The forward and reverse processes cancel each other out, and no net chemical change occurs.
A displacement reaction is when a more reactive metal takes the place of a less reactive metal in a salt solution. The more reactive metal loses electrons and goes into solution as ions, while the less reactive metal ions gain electrons and come out as solid metal. For example, zinc displaces copper from copper sulphate solution.
The reactivity series is a ranking of metals from most reactive (potassium at the top) to least reactive (gold at the bottom). It tells you which metals can displace which. Any metal higher in the series can displace any metal below it from its salt solution. Hydrogen is included as a reference point metals above it react with acids.
No. Copper metal placed in copper sulphate solution shows no reaction. The copper atoms and copper ions (Cu²⁺) are the same element, so there’s no driving force for any electron transfer. The system is already at equilibrium. No colour change, no deposit, no reaction.
Zinc reacts with copper sulphate because zinc sits above copper in the activity series zinc is more reactive and can displace copper ions from solution. But zinc can’t react with zinc sulphate because zinc and its own ions (Zn²⁺) are the same element. There’s no reactivity gap to exploit, so nothing happens.
Nothing happens. Iron metal and the iron ions (Fe²⁺) in iron sulphate solution are the same element. No displacement is possible because you’d need a more reactive metal to displace iron, and iron can’t be more reactive than itself. The iron strip just sits there unchanged.
Check the activity series. Find the metal being added and the metal in the salt solution. If the added metal is higher in the activity series, displacement occurs. If it’s lower or the same, no reaction occurs. Same metal as the salt? Always no reaction. This method works for every question you’ll see in exams.
The free energy change (ΔG) for a metal reacting with its own salt is zero. In thermodynamics, reactions happen spontaneously only when ΔG is negative. When a metal meets its own ions, the energy cost of the metal going into solution equals the energy released by the ions coming out they’re identical processes. Net energy change: zero. Net reaction: zero.
Zinc displaces copper from copper sulphate (Zn + CuSO₄ → ZnSO₄ + Cu). Iron displaces copper from copper sulphate (Fe + CuSO₄ → FeSO₄ + Cu). Magnesium displaces zinc from zinc sulphate (Mg + ZnSO₄ → MgSO₄ + Zn). In each case, the metal added is higher in the activity series than the metal in the salt.
The metal being added must be more reactive than the metal in the salt solution meaning it must sit higher in the activity series. If the added metal is less reactive or equally reactive (including being the same metal), no reaction occurs. One metal, one salt solution, one condition: higher reactivity wins.
You can summarise everything on this page in a single sentence:
A metal can only displace a metal less reactive than itself and since no metal is less reactive than itself, a metal will never react with its own salt.
That’s the chemistry. That’s the logic. And that’s exactly what your examiner wants to see in your answer.
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