Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

6.2.4Additional lessons

Acids with Reactive Metals — IB Chemistry SL Revision Notes & Topical Questions

5 min read 6 parts Lesson 87 of 98

📚 IB Chemistry SL Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
0%read

Part 1 of 6The General Reaction

Metals above hydrogen in the reactivity series can displace it from dilute acids.

Word equation
  • Word equation Reactive metal + dilute acid → salt + hydrogen.
Magnesium
  • Magnesium Magnesium gives magnesium chloride and hydrogen: Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g).
Zinc
  • Zinc Zinc with sulfuric acid gives: Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g).
Iron
  • Iron Fe(s) + 2HCl(aq) → FeCl₂(aq) + H₂(g), forming iron(II) rather than iron(III).

Part 2 of 6Redox Analysis

Redox Analysis
Oxidation
  • Oxidation The metal loses electrons and its oxidation number increases, for example Mg: 0 → +2.
Reduction
  • Reduction H⁺ gains electrons to form H₂, so hydrogen goes from +1 to 0.
Ionic equation
  • Ionic equation Mg(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂(g); the anion is a spectator.
Reducing agent
  • Reducing agent The metal is the reducing agent and the acid supplies the oxidising agent H⁺.

Part 3 of 6Observations and Tests

1
Effervescence shows that hydrogen gas is being made.
2
The metal slowly dissolves, and the test tube becomes warm because the reaction is exothermic.
3
A lit splint held at the mouth of the tube burns with a squeaky pop.
4
More reactive metals react faster, so rate order is Mg > Zn > Fe.
5
Copper, silver and gold lie below hydrogen and do not react with dilute acids.

Part 4 of 6Linking to Reactivity

Linking to Reactivity
Order of reactivity
  • Order of reactivity Rate of hydrogen production increases from iron to zinc to magnesium, reflecting the ease of oxidation.
Safety
  • Safety Hydrogen is flammable, so the gas should be collected away from flames and tested in small quantities.
Evidence of redox
  • Evidence of redox The disappearance of the metal and the formation of H₂ show electrons being transferred from metal to H⁺.
Sulfuric acid note
  • Sulfuric acid note Dilute sulfuric acid with lead stops quickly because insoluble lead(II) sulfate coats the metal.

Part 5 of 6Worked Example

Question

  • Calculate the volume of hydrogen released at STP when 0.250 g of magnesium reacts with excess dilute hydrochloric acid.
  • Molar volume of a gas at STP is 22.7 dm³ mol⁻¹.

  1. Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g), so 1 mol Mg gives 1 mol H₂.
  2. n(Mg) = 0.250 / 24.31 = 0.01028 mol, so n(H₂) = 0.01028 mol.
  3. V = 0.01028 × 22.7 = 0.233 dm³.

Answer 0.233 dm³ (233 cm³) of hydrogen.

Part 6 of 6Exam Checklist & Tips

6.2.4 – Key Points for the Exam

  • Salt The ionic compound formed when metal replaces hydrogen in an acid.
  • Spectator ion An ion present but not changing in the reaction, such as Cl⁻.
  • Reactivity series The order of metals by ease of oxidation.
  • Effervescence The formation of gas bubbles in a liquid.

Common Mistakes

  • Writing iron(III) chloride as the product with dilute HCl; the product is iron(II) chloride.
  • Saying that all metals react with dilute acids, forgetting that copper does not.
  • Using dilute nitric acid as a typical example: nitrate is reduced, so H₂ is not the usual product.
  • Leaving the equation unbalanced, for example Mg + HCl → MgCl₂ + H₂.

Last updated:

\n