NDA Chemistry · Metals and Non-Metals

Alloys and Their Composition

Alloys are solid mixtures of a metal with one or more other elements — brass, bronze, steel, amalgam — engineered to beat the pure metal on strength, hardness or corrosion resistance.

All Metals and Non-Metals notes NDA Chemistry strategy

Why this matters

A reliable recall pocket — about 4 PYQs. The bank asks the composition of a named alloy (bronze = Cu + Sn), which alloy contains a non-metal (steel = Fe + C), the coolant alloy in nuclear reactors (NaK), and which metal is NOT essential to stainless steel. Learn the name↔composition table and these are one-line answers.

Concept 1 of 2

Common alloys and their composition

Intuition

An alloy mixes a base metal with other elements to improve its properties — brass and bronze are both copper-based, steel adds carbon to iron, amalgam dissolves a metal in mercury. The bank simply asks 'X is an alloy of what?', so memorise each composition.

Definition

The high-frequency name↔composition facts:

Brass = copper + zinc (Cu + Zn).
Bronze = copper + tin (Cu + Sn).
Steel = iron + carbon (Fe + C) — carbon, a non-metal, is the alloying element.
Stainless steel = iron + chromium + nickel (+ carbon); essential components are Fe, Cr and Ni — tin is NOT part of it.
Amalgam = an alloy in which one component is mercury (Hg + another metal).
Solder = lead + tin (Pb + Sn).
Duralumin = aluminium + copper + magnesium + manganese.

Alloy	Composition	Note
Brass	Copper + Zinc	Both metals
Bronze	Copper + Tin	Cu + Sn — the bank's favourite composition question
Steel	Iron + Carbon	Carbon is a non-metal — the 'alloy with a non-metal' answer Steel is the alloy that contains a NON-METAL (carbon). Brass, bronze and amalgam are metal-only.
Stainless steel	Iron + Chromium + Nickel (+ C)	Tin is NOT an essential component Essential components of stainless steel are Fe, Cr and Ni — tin is the odd one out.
Amalgam	Mercury + another metal	Mercury-based alloy
Solder	Lead + Tin	Low-melting joining alloy

Brass = Cu+Zn, Bronze = Cu+Sn, Steel = Fe+C, Stainless steel = Fe+Cr+Ni, Amalgam = Hg-based.

Practice this conceptself-check · 5 quick reps

From the bank · past-year question

Example 1Metals and Non-MetalsEASY

Bronze is an alloy of

[Q103 · Sep · 2022]

Brass vs bronze — don't swap zinc and tin

Brass = copper + zinc; bronze = copper + tin. Both are copper-based, so the trap is mixing up the second metal — zinc for brass, tin for bronze.

Tin is not in stainless steel

Stainless steel's essential metals are iron, chromium and nickel. Tin belongs to bronze and solder, not stainless steel — it is the 'NOT essential' answer.

Drill 2 more on common alloys and their composition

Concept 2 of 2

Special-purpose alloys

Intuition

Some alloys are made for one specific job. The sodium-potassium (NaK) alloy is liquid over a wide range and conducts heat extremely well, so it is used as a coolant to transfer heat in nuclear reactors. The bank tests this one directly: which metal is alloyed with sodium to transfer heat in a reactor?

Definition

Special-purpose alloy facts:

NaK = sodium + potassium. It is liquid over a wide temperature range and is used as a heat-transfer coolant in nuclear reactors.
Type metal = lead + tin + antimony (printing type).
Magnalium = aluminium + magnesium (light, strong).
Nichrome = nickel + chromium (heating elements; high resistance).

Alloy	Composition	Special use
NaK	Sodium + Potassium	Coolant / heat transfer in nuclear reactors Potassium is alloyed with sodium (NaK) to transfer heat in nuclear reactors.
Nichrome	Nickel + Chromium	Heating elements (high resistance)
Magnalium	Aluminium + Magnesium	Light, strong structural parts
Type metal	Lead + Tin + Antimony	Printing type

NaK (sodium + potassium) is the nuclear-reactor heat-transfer coolant.

Practice this concept3 quick reps

From the bank · past-year question

Example 2Metals and Non-MetalsMODERATE

Which one of the following metals is alloyed with sodium to transfer heat in a nuclear reactor?

[Q107 · Apr · 2018]

NaK coolant uses potassium, not calcium

The reactor heat-transfer alloy is sodium + potassium (NaK). Calcium, magnesium and strontium are distractors — the partner metal alloyed with sodium is potassium.

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Reference tables (2)

Common alloys and their composition6 rows

Alloy	Composition	Note
Brass	Copper + Zinc	Both metals
Bronze	Copper + Tin	Cu + Sn — the bank's favourite composition question
Steel	Iron + Carbon	Carbon is a non-metal — the 'alloy with a non-metal' answer Steel is the alloy that contains a NON-METAL (carbon). Brass, bronze and amalgam are metal-only.
Stainless steel	Iron + Chromium + Nickel (+ C)	Tin is NOT an essential component Essential components of stainless steel are Fe, Cr and Ni — tin is the odd one out.
Amalgam	Mercury + another metal	Mercury-based alloy
Solder	Lead + Tin	Low-melting joining alloy

Brass = Cu+Zn, Bronze = Cu+Sn, Steel = Fe+C, Stainless steel = Fe+Cr+Ni, Amalgam = Hg-based.

Special-purpose alloys4 rows

Alloy	Composition	Special use
NaK	Sodium + Potassium	Coolant / heat transfer in nuclear reactors Potassium is alloyed with sodium (NaK) to transfer heat in nuclear reactors.
Nichrome	Nickel + Chromium	Heating elements (high resistance)
Magnalium	Aluminium + Magnesium	Light, strong structural parts
Type metal	Lead + Tin + Antimony	Printing type

NaK (sodium + potassium) is the nuclear-reactor heat-transfer coolant.

Watch out for (3)

Brass vs bronze — don't swap zinc and tin
→ Common alloys and their composition
Tin is not in stainless steel
→ Common alloys and their composition
NaK coolant uses potassium, not calcium
→ Special-purpose alloys

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