3.1.4Additional lessons
Group 1 Metals with Water — IB Chemistry HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 51 of 172
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.
Part 1 of 5Observations
Each Group 1 metal reacts with cold water to give hydrogen gas and a metal hydroxide solution.
Lithium
- Lithium Lithium floats and fizzes steadily as hydrogen forms, and it dissolves slowly without melting.
Sodium
- Sodium Sodium melts into a silvery ball that darts around the surface, fizzing rapidly as it reacts.
Potassium
- Potassium Potassium reacts so vigorously that the hydrogen ignites with a lilac flame, and the metal melts as it moves.
Solution formed
- Solution formed The resulting solution turns universal indicator purple, showing a strongly alkaline hydroxide with pH about 13 to 14.
Heavier metals
- Heavier metals Rubidium and caesium react explosively, so these experiments are not carried out in school laboratories.
Part 2 of 5Equation and Explanation
1
The general equation is 2M(s) + 2H₂O(l) → 2MOH(aq) + H₂(g), where M is any Group 1 metal.
2
The metal atom loses its single outer electron to form M⁺, so the reaction is an oxidation of the metal.
3
Water is reduced to hydrogen gas, and the OH⁻ ions produced make the solution alkaline.
4
Going down the group the outer electron is further from the nucleus and better shielded, so it is removed more easily.
5
Lower first ionisation energy therefore explains the increasing rate and violence of the reaction.
| Metal | Equation |
|---|---|
| Li | 2Li(s) + 2H₂O(l) → 2LiOH(aq) + H₂(g) |
| Na | 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) |
| K | 2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g) |
Part 3 of 5Safety and Handling
Safety and Handling
Storage
- Storage Group 1 metals are stored under oil to prevent reaction with moisture and oxygen in the air.
Small pieces
- Small pieces Only rice-grain pieces are used, with a safety screen and eye protection, because of the risk of spitting and ignition.
Hydrogen
- Hydrogen Hydrogen is flammable, so the gas collected must be kept away from flames except in a controlled test.
Hydroxides
- Hydroxides The solutions formed are corrosive, and spills should be diluted with plenty of water.
Part 4 of 5Worked Example
Question
- 0.23 g of sodium reacts completely with water to give 100 cm³ of solution.
- Calculate the volume of hydrogen at STP (molar volume 22.7 dm³ mol⁻¹) and the concentration of NaOH.
- n(Na) = 0.23 ÷ 22.99 = 0.0100 mol.
- From 2Na : 1H₂, n(H₂) = 0.00500 mol, so V = 0.00500 × 22.7 = 0.1135 dm³ ≈ 114 cm³.
- n(NaOH) = 0.0100 mol in 0.100 dm³.
- [NaOH] = 0.0100 ÷ 0.100 = 0.100 mol dm⁻³.
Answer
- V(H₂) ≈ 114 cm³;
- [NaOH] = 0.100 mol dm⁻³
Part 5 of 5Exam Checklist & Tips
3.1.4 – Key Points for the Exam
- Alkali metal A Group 1 element, which forms strongly alkaline hydroxides.
- Oxidation Loss of electrons, as when Na becomes Na⁺.
- Metal hydroxide An ionic compound containing M⁺ and OH⁻ ions that dissolves to give an alkaline solution.
- Reactivity Tendency of a metal to lose electrons and form positive ions.
Common Mistakes
- Writing the product as a metal oxide rather than a hydroxide.
- Leaving out state symbols or using (aq) for the metal.
- Explaining the trend by 'larger atom' only, without referring to ionisation energy and shielding.
- Saying the metals sink; they float because they are less dense than water.
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