What Happens When Metals React with Acids? (With Equations & Examples)
The Reaction Of Metals With Acids is a classic and highly tested concept in JEE Main Chemistry, showing how metals interact with acids to form salts and hydrogen gas. This predictable transformation is vital for understanding displacement reactions and is closely linked to the chemical properties of metals, the reactivity series, and equations you must master for exams. Let’s break down the mechanism, typical equations, key examples, energetic reactivity, and how metal-acid reactions relate to other acid-base concepts in the JEE syllabus.
What Are Reactions of Metals with Acids?
Metals react with acids to form a salt and hydrogen gas (H2). This process occurs readily with most reactive metals and is easily observed by the characteristic effervescence due to hydrogen evolution. The reactivity depends on both the metal and acid, but the key products are always a salt (metal cation + acid anion) and hydrogen.
General Equation and Word Equation for Acid Metal Reactions
In JEE, you need to remember the universal pattern:
| Format | Example |
|---|---|
| Word Equation | Metal + Acid → Salt + Hydrogen gas |
| General Chemical Equation | M + 2HCl → MCl2 + H2↑ |
| Example: Zinc + Hydrochloric Acid | Zn + 2HCl → ZnCl2 + H2↑ |
This general equation helps you quickly write balanced reactions. The salt’s name comes from the metal and acid—e.g., magnesium + sulfuric acid forms magnesium sulfate.
Mechanism and Why the Reaction Occurs
The reaction of metals with acids is a redox process—the metal is oxidized, losing electrons to form a cation, while H+ from the acid is reduced, gaining electrons to form H2 gas. In effect, the metal “displaces” hydrogen from the acid (single displacement reaction), which is why this is grouped with redox reactions in JEE.
- Only metals above hydrogen in the reactivity series will react with dilute acids.
- Electron transfer is central: M → M2+ + 2e-; 2H+ + 2e- → H2↑.
The rate and vigor of the reaction depend on the metal’s position in the reactivity series and whether the acid is dilute. Highly reactive metals (e.g., sodium, potassium) will react explosively.
Key Examples: Important Metals and Observations
| Metal | Dilute Acid | Salt Formed | Equation | Observation |
|---|---|---|---|---|
| Magnesium | HCl | MgCl2 | Mg + 2HCl → MgCl2 + H2 | Rapid effervescence; metal dissolves quickly. |
| Zinc | H2SO4 | ZnSO4 | Zn + H2SO4 → ZnSO4 + H2 | Bubbles form; zinc granules diminish. |
| Iron | HCl | FeCl2 | Fe + 2HCl → FeCl2 + H2 | Slower reaction; pale green solution. |
| Aluminium | HCl | AlCl3 | 2Al + 6HCl → 2AlCl3 + 3H2 | Initially slow (oxide layer), then vigorous. |
| Sodium | H2SO4 | Na2SO4 | 2Na + H2SO4 → Na2SO4 + H2 | Violent/fires; not done in lab! |
Notice how hydrogen gas is always evolved—often confirmed by a ‘pop’ sound when tested with a burning splint in the lab.
Metals That Don’t React with Acids and Violent Reactivity Traps
- Copper, Silver, and Gold do not react with dilute acids like HCl or H2SO4. They are below hydrogen in the reactivity series.
- Sodium, Potassium react dangerously fast and explosively with acids—never attempt in the school lab!
- Lead shows slow or no reaction with cold dilute acids due to insoluble PbSO4 coating.
The absence or extremity of reaction depends on both the position in the reactivity series and acid concentration. Exam MCQs often test these exceptions.
Applications of Metal-Acid Reactions
- Industrial production of hydrogen gas uses zinc and dilute sulfuric acid.
- Testing for hydrogen gas in lab: ‘pop’ sound acts as confirmatory evidence.
- Cleaning metals before galvanizing—acid removes surface oxides.
- Principle in extraction of metals and metallurgy.
Every example reinforces your ability to balance equations, predict products, and apply safety knowledge backing many practical and industrial JEE questions.
Relation to Other Acid Reactions: Bases, Oxides, and Carbonates
The concept links directly to other key chemistry reactions: Acids, Bases and Salts.
| Reactant | General Reaction | Salt Example | Gas Evolved |
|---|---|---|---|
| Metal | Metal + Acid → Salt + H2 | MgCl2 | Hydrogen (H2) |
| Metal Oxide | Metal Oxide + Acid → Salt + H2O | CuSO4 | None |
| Metal Carbonate | Carbonate + Acid → Salt + H2O + CO2 | CaCl2 | Carbon dioxide (CO2) |
| Base (Alkali) | Base + Acid → Salt + H2O | NaCl | None |
Comparing these reactions helps you avoid confusion between displacement (with metals) and neutralisation (with bases) in JEE MCQs.
Sample JEE-Style Questions for Acid Metal Reactions
- Write the balanced chemical equation: Iron reacts with dilute sulfuric acid.
- Which of the following metals does NOT react with dilute HCl? (a) Mg (b) Ca (c) Cu (d) Zn
- Name the gas evolved when zinc reacts with hydrochloric acid and state the test for it.
- Which metal reacts violently with dilute acids? (a) Na (b) Ag (c) Fe (d) Pb
- Give an example of a metal that does not evolve hydrogen gas with dilute acids.
Practicing such questions is key for scoring in application and recall portions of JEE Main Chemistry.
Summary Table: Metal + Acid → Salt + Hydrogen
| Metal Example | Equation | Vigor of Reaction |
|---|---|---|
| Mg + HCl | Mg + 2HCl → MgCl2 + H2 | Rapid |
| Fe + H2SO4 | Fe + H2SO4 → FeSO4 + H2 | Moderate |
| Cu + HCl | No observable reaction | None |
Mastering such details helps quickly recall and write equations under exam pressure. For deeper insights, review the chemical properties of metals and the hydrogen gas preparation articles.
- Study the types of redox reactions for more equation tricks.
- Connect with extraction of metals for real-world usage of acid-metal interactions in metallurgy.
- Explore related chemical equations for JEE revision.
The topic “Reaction Of Metals With Acids” is a must-know for routine JEE Main Chemistry problems, so practice writing, balancing, and predicting these reactions with confidence. Vedantu supports your conceptual clarity with more linked resources throughout our JEE Chemistry pages.
FAQs on Reaction of Metals with Acids: Explanation, Equations, and Examples
1. What happens when metals react with acid?
When metals react with acids, they form a salt and hydrogen gas. This classic reaction can be represented by the general equation:
- Metal + Acid → Salt + Hydrogen gas
2. What are 5 examples of acid and metal reactions?
Five common examples of metal reacting with acid and forming salt plus hydrogen gas are:
- Zinc + Hydrochloric acid → Zinc chloride + Hydrogen (Zn + 2HCl → ZnCl2 + H2)
- Magnesium + Sulphuric acid → Magnesium sulphate + Hydrogen (Mg + H2SO4 → MgSO4 + H2)
- Iron + Hydrochloric acid → Iron(II) chloride + Hydrogen (Fe + 2HCl → FeCl2 + H2)
- Aluminium + Hydrochloric acid → Aluminium chloride + Hydrogen (2Al + 6HCl → 2AlCl3 + 3H2)
- Sodium + Hydrochloric acid → Sodium chloride + Hydrogen (2Na + 2HCl → 2NaCl + H2) – highly violent reaction
3. What is the general word equation for metal and acid reaction?
The general word equation for the reaction of metals with acids is:
- Metal + Acid → Salt + Hydrogen
4. Which metal reacts violently with acids?
Metals like sodium and potassium react violently with acids. These are very reactive metals in the reactivity series and can cause explosions or fires when exposed to dilute acids. Precautions are needed when handling such reactions in the lab.
5. Are there metals that do not react with acids?
Yes, some metals do not react with dilute acids under normal conditions. Examples include:
- Copper (Cu)
- Silver (Ag)
- Gold (Au)
6. Why doesn’t copper react with dilute acids, while zinc does?
Copper does not react with dilute acids because it is less reactive than hydrogen. In the reactivity series of metals:
- Zinc is above hydrogen, so it displaces hydrogen from acids easily.
- Copper is below hydrogen, so it cannot displace hydrogen from acids.
7. Can all acids react with all metals?
No, not all acids react with all metals.
- Only acids capable of releasing hydrogen ions (like hydrochloric acid and sulphuric acid) can generally react with reactive metals.
- Not all metals are reactive enough; for example, gold does not react with regular acids.
- Some acids (like nitric acid) can give different products due to their oxidising nature.
8. Why is hydrogen gas not produced when nitric acid reacts with metals?
Hydrogen gas is usually not evolved when metals react with nitric acid because nitric acid is a strong oxidising agent. Instead of hydrogen gas, other gases such as nitrogen dioxide (NO2) or nitric oxide (NO) are released because nitric acid oxidises the hydrogen to water.
9. How are reactions of metals with acids applied in the lab and industry?
Reactions of metals with acids have several practical uses:
- Hydrogen gas production for lab experiments and industry
- Preparation of salts for various laboratory and industrial purposes
- Metal extraction processes often involve acid treatment (metallurgy)
- Testing metal reactivity and placement in the reactivity series
10. What safety measures should be taken when demonstrating metal-acid reactions?
When demonstrating metal-acid reactions, important safety measures include:
- Always wear safety goggles and lab gloves
- Use dilute acids only to minimize the risk
- Add acid to water, not the other way around
- Avoid very reactive metals such as sodium or potassium in open demonstrations
- Ensure good ventilation to safely disperse hydrogen gas
