NDA Chemistry · Industrial and Applied Chemistry

Common Industrial Substances and Alloys

The composition of everyday industrial substances and alloys — plaster of Paris, borax, soft soap and solder — plus the raw materials of Portland cement, all answered by knowing one formula or element list per item.

All Industrial and Applied Chemistry notes NDA Chemistry strategy

Why this matters

Five PYQs of pure composition recall. The bank asks 'solder is an alloy of...', 'the formula of plaster of Paris is...', or 'soft soap contains...'. Each is a single fact: solder = Pb + Sn, plaster of Paris = CaSO₄·½H₂O, soft soap = potassium soap, borax = Na, B, O, H.

Concept 1 of 3

Common alloys and their composition

Intuition

An alloy is a mixture of metals. The bank asks the two (or more) metals in a named alloy. Solder is the high-frequency one — learn its pair first, then the rest.

Definition

The alloy composition facts:

Solder = lead (Pb) + tin (Sn) — a low-melting alloy for joining metals.
Brass = copper (Cu) + zinc (Zn).
Bronze = copper (Cu) + tin (Sn).
Steel = iron (Fe) + carbon (C).
Duralumin = aluminium (Al) + copper (Cu) + magnesium + manganese.

Alloy	Composition	Use
Solder	Lead (Pb) + tin (Sn)	Joining/soldering metals Solder is an alloy of lead and tin (Pb + Sn).
Brass	Copper + zinc (Cu + Zn)	Fittings, instruments
Bronze	Copper + tin (Cu + Sn)	Statues, coins, bearings
Steel	Iron + carbon (Fe + C)	Construction, tools
Duralumin	Al + Cu + Mg + Mn	Aircraft (light, strong)

Practice this conceptself-check · 4 quick reps

Try it yourself

Name the metals in solder and in brass.

Practice — Level 1 (4 reps)

Quick reps to lock in the method. Try each, then check.

1.
Solder is an alloy of which two metals?
2.
Brass is an alloy of which two metals?
3.
Bronze is an alloy of which two metals?
4.
Steel is iron alloyed with what?

From the bank · past-year question

Example 1Industrial and Applied ChemistryEASY

Solder is an alloy of

[Q60 · Apr · 2021]

Solder = Pb + Sn, brass = Cu + Zn, bronze = Cu + Sn

Keep the copper alloys apart: brass is copper + ZINC, bronze is copper + TIN. Solder is lead + tin (no copper). The bank swaps these as distractors.

Concept 2 of 3

Plaster of Paris, borax and soft soap

Intuition

A short list of named industrial substances, each with one fact the bank wants: a formula, an element list, or the metal in a soap. Learn one line each.

Definition

The named-substance facts:

Plaster of Paris = CaSO₄·½H₂O (calcium sulphate hemihydrate), made by heating gypsum. Sets hard when mixed with water.
Borax is composed of sodium, boron, oxygen and hydrogen (Na₂B₄O₇·10H₂O).
Soft soap is a potassium soap — it contains potassium (hard soap is the sodium salt). Soft soap is more soluble and used in liquid/shaving soaps.

Substance	Formula / composition	Key fact
Plaster of Paris	CaSO₄·½H₂O	Calcium sulphate hemihydrate; from gypsum Plaster of Paris = CaSO₄·½H₂O (½ water per CaSO₄), not CaSO₄·2H₂O (that is gypsum).
Borax	Na, B, O, H (Na₂B₄O₇·10H₂O)	Sodium tetraborate decahydrate Borax contains sodium, boron, oxygen and hydrogen.
Soft soap	Potassium soap	Contains potassium (K) Soft soap = potassium salt; HARD soap = sodium salt.

Practice this conceptself-check · 4 quick reps

Try it yourself

A sample of 'soft soap' contains which metal — sodium or potassium? What about ordinary hard soap?

Practice — Level 1 (4 reps)

Quick reps to lock in the method. Try each, then check.

1.
What is the chemical formula of plaster of Paris?
2.
Soft soap contains which metal?
3.
Which four elements make up borax?
4.
Plaster of Paris is made by heating which mineral?

From the bank · past-year question

Example 2Industrial and Applied ChemistryEASY

Which one of the following is the chemical formula of Plaster of Paris?

[Q144 · Sep · 2021]

Soft soap = potassium, hard soap = sodium

Soft soap is the POTASSIUM salt of a fatty acid (more soluble, used in liquid soaps); ordinary hard bar soap is the SODIUM salt. The bank asks which metal soft soap contains — answer potassium.

Plaster of Paris is ½ water, gypsum is 2 waters

Plaster of Paris is CaSO₄·½H₂O; gypsum is CaSO₄·2H₂O. Picking the 2-water formula for plaster of Paris is the standard mistake.

Drill 2 more on plaster of paris, borax and soft soap

Concept 3 of 3

Raw materials of Portland cement

Intuition

Two of the bank's cement questions are filed here under industrial substances. The raw materials are the same lime–silica–alumina list as the building-materials subtopic — learn it once.

Definition

The raw materials of Portland cement:

Lime (CaO) — from limestone / calcium carbonate.
Silica (SiO₂) — from clay or sand.
Alumina (Al₂O₃) — from clay.
Plus a little iron oxide. A small amount of gypsum is added at the end to control setting time.

Raw material	Provides	Source
Limestone	Lime (CaO)	Calcium carbonate rock
Clay / sand	Silica (SiO₂)	Clay, sand
Clay	Alumina (Al₂O₃)	Aluminosilicate clay
Iron ore + gypsum	Iron oxide; setting control	Added in small amounts Lime, silica and alumina are the essential trio — gypsum is only a setting regulator.

Practice this concept3 quick reps

Practice — Level 1 (3 reps)

Quick reps to lock in the method. Try each, then check.

1.
Name the three essential raw materials of Portland cement.
2.
Which raw material provides lime in cement?
3.
Why is gypsum added to cement?

From the bank · past-year question

Example 3Industrial and Applied ChemistryEASY

The raw materials used for the manufacture of Portland cement are

[Q60 · Sep · 2019]

Lime + silica + alumina is the trio

The essential raw materials of Portland cement are lime, silica and alumina. Gypsum is added only to control setting time — it is not one of the three essential constituents.

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 (3)

Common alloys and their composition5 rows

Alloy	Composition	Use
Solder	Lead (Pb) + tin (Sn)	Joining/soldering metals Solder is an alloy of lead and tin (Pb + Sn).
Brass	Copper + zinc (Cu + Zn)	Fittings, instruments
Bronze	Copper + tin (Cu + Sn)	Statues, coins, bearings
Steel	Iron + carbon (Fe + C)	Construction, tools
Duralumin	Al + Cu + Mg + Mn	Aircraft (light, strong)

Plaster of Paris, borax and soft soap3 rows

Substance	Formula / composition	Key fact
Plaster of Paris	CaSO₄·½H₂O	Calcium sulphate hemihydrate; from gypsum Plaster of Paris = CaSO₄·½H₂O (½ water per CaSO₄), not CaSO₄·2H₂O (that is gypsum).
Borax	Na, B, O, H (Na₂B₄O₇·10H₂O)	Sodium tetraborate decahydrate Borax contains sodium, boron, oxygen and hydrogen.
Soft soap	Potassium soap	Contains potassium (K) Soft soap = potassium salt; HARD soap = sodium salt.

Raw materials of Portland cement4 rows

Raw material	Provides	Source
Limestone	Lime (CaO)	Calcium carbonate rock
Clay / sand	Silica (SiO₂)	Clay, sand
Clay	Alumina (Al₂O₃)	Aluminosilicate clay
Iron ore + gypsum	Iron oxide; setting control	Added in small amounts Lime, silica and alumina are the essential trio — gypsum is only a setting regulator.

Watch out for (4)

Solder = Pb + Sn, brass = Cu + Zn, bronze = Cu + Sn
→ Common alloys and their composition
Soft soap = potassium, hard soap = sodium
→ Plaster of Paris, borax and soft soap
Plaster of Paris is ½ water, gypsum is 2 waters
→ Plaster of Paris, borax and soft soap
Lime + silica + alumina is the trio
→ Raw materials of Portland cement

Mastery check — 2 interleaved questions

Try each one before clicking. Questions are interleaved across the concepts above, not grouped — interleaving sharpens transfer.

Example 1Industrial and Applied ChemistryEASY

Which among the following is the correct composition of Borax ?

[Q106 · Apr · 2024]

Example 2Industrial and Applied ChemistryEASY

A sample of 'soft soap' contains

[Q62 · Sep · 2019]

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