2.4.3Additional lessons
Properties of Alloys — IB Chemistry HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 45 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 5What Alloys Are
Alloying changes the arrangement of atoms in a metal and therefore its properties.
Definition
- Definition An alloy is a mixture of a metal with other elements, which are usually metals but may include carbon.
Solid solution
- Solid solution Atoms of the added element are spread through the lattice of the main metal.
Metallic bonding
- Metallic bonding Alloys remain metallic, so they conduct electricity and are shiny.
Purpose
- Purpose Alloys are made to improve strength, hardness or resistance to corrosion.
Part 2 of 5Why Alloys Are Harder
Why Alloys Are Harder
Regular layers
- Regular layers In a pure metal identical atoms form neat layers that slide over each other easily.
Different sizes
- Different sizes Atoms of another element disturb the regular pattern of the lattice.
Blocked movement
- Blocked movement Layers can no longer slide easily, so the alloy is harder and stronger.
Trade-off
- Trade-off The alloy is usually less malleable and ductile than the pure metal.
Part 3 of 5Common Alloys
Brass
- Brass Copper with zinc, used for musical instruments and fittings because it is hard and resists corrosion.
Bronze
- Bronze Copper with tin, used for statues, bearings and ship fittings.
Steel
- Steel Iron with a small percentage of carbon, harder and stronger than pure iron.
Stainless steel
- Stainless steel Iron with chromium and nickel, which resists rusting.
| Alloy | Main metal | Added element |
|---|---|---|
| Brass | Copper | Zinc |
| Bronze | Copper | Tin |
| Steel | Iron | Carbon |
| Solder | Tin | Other metals such as silver |
Part 4 of 5Changes in Other Properties
1
Electrical conductivity is usually lower than that of the pure metal because foreign atoms scatter the moving electrons.
2
The melting point may be lower, which is why solder melts easily and is useful for joining wires.
3
Corrosion resistance can improve, as when chromium forms a protective oxide layer in stainless steel.
4
Careful choice of added elements and proportions allows an alloy to be designed for a specific use.
Part 5 of 5Exam Checklist & Tips
2.4.3 – Key Points for the Exam
- Alloy A mixture of a metal with one or more other elements.
- Pure metal A metal made of a single type of atom in a regular lattice.
- Brass An alloy of copper and zinc.
- Steel An alloy of iron and carbon.
Common Mistakes
- Calling an alloy a compound; it is a mixture with no fixed ratio.
- Saying alloys are harder because atoms are bonded covalently.
- Stating that alloys conduct better than pure metals.
- Forgetting that atoms of different size disrupt the layers.
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