NDA Chemistry · Carbon and Its Compounds

Common Carbon Compounds and Pigments

The everyday names, formulas and uses of carbonate and bicarbonate compounds, their waters of crystallization, and the pigments used in paints.

All Carbon and Its Compounds notes NDA Chemistry strategy

Why this matters

Ten PYQs of name↔formula↔use recall — washing soda, baking soda, dry ice, chalk — plus the water-of-crystallization counts and a 'which is not a pigment' trap. This is a memorise-the-table subtopic; the only catch is the hydration numbers.

Concept 1 of 3

Common names, formulas and uses

Intuition

The bank keeps a short list of household carbon compounds and asks the formula, the common name, or the use — any of the three columns. Learn all three for each.

Definition

The high-frequency name↔formula↔use facts:

Washing soda = Na₂CO₃·10H₂O (sodium carbonate decahydrate).
Baking soda = NaHCO₃ (sodium bicarbonate).
Dry ice = solid CO₂ (sublimes directly to gas; used as a refrigerant).
Chalk and marble = CaCO₃ (calcium carbonate).
Vinegar = acetic acid (ethanoic acid, a dilute solution).
Silica gel = a desiccant (drying agent that absorbs moisture).

Common name	Chemical name / formula	Use or identity
Washing soda	Na₂CO₃·10H₂O	Cleaning, water softening
Baking soda	NaHCO₃	Baking, antacid
Dry ice	Solid CO₂	Refrigerant — sublimes, no liquid Dry ice is solid carbon dioxide, NOT frozen water.
Chalk / Marble	CaCO₃	Building, blackboard chalk
Vinegar	Acetic (ethanoic) acid	Food preservative, flavouring
Silica gel	SiO₂ (hydrated)	Desiccant — absorbs moisture

Practice this concept5 quick reps

Practice — Level 1 (5 reps)

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

1.
Chemical formula of washing soda?
2.
Dry ice (in solid form) is which compound?
3.
Chalk and marble are different forms of which compound?
4.
Vinegar is also known as?
5.
Best example of a desiccant?

From the bank · past-year question

Example 1Carbon and Its CompoundsEASY

Which one of the following is the chemical formula of Washing Soda?

[Q67 · Apr · 2018]

Dry ice is CO₂, not ice

'Dry ice' is solid carbon dioxide, not frozen water. It sublimes (solid → gas) with no liquid stage, which is why it is 'dry'.

Drill 5 more on common names, formulas and uses

Concept 2 of 3

Water of crystallization

Intuition

Water of crystallization is the fixed number of water molecules locked into a crystal's structure, written after a dot in the formula. The bank asks for the count for a few specific salts — memorise the numbers.

Definition

The hydration numbers the bank tests:

Blue vitriol (copper sulphate) = CuSO₄·5H₂O → 5.
Washing soda (sodium carbonate) = Na₂CO₃·10H₂O → 10.
Gypsum (calcium sulphate) = CaSO₄·2H₂O → 2.
Plaster of Paris = (CaSO₄)₂·H₂O (i.e. CaSO₄·½H₂O) → one water shared between two formula units of CaSO₄.

Salt	Formula	Water molecules
Blue vitriol (copper sulphate)	CuSO₄·5H₂O	5
Washing soda	Na₂CO₃·10H₂O	10
Gypsum	CaSO₄·2H₂O	2
Plaster of Paris	(CaSO₄)₂·H₂O	1 (shared by two CaSO₄ units) Plaster of Paris has ONE water of crystallization per TWO formula units of CaSO₄ — i.e. CaSO₄·½H₂O.

Practice this concept4 quick reps

Practice — Level 1 (4 reps)

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

1.
Waters of crystallization in copper sulphate (blue vitriol)?
2.
Waters of crystallization in washing soda?
3.
Waters of crystallization in gypsum?
4.
How many water molecules does plaster of Paris share between two CaSO₄ units?

From the bank · past-year question

Example 2Carbon and Its CompoundsMODERATE

Number of molecules of water of crystallization in copper sulphate, sodium carbonate and Gypsum are

[Q144 · Apr · 2020]

Plaster of Paris = half a water per CaSO₄

Plaster of Paris is written (CaSO₄)₂·H₂O — one water molecule shared by two units of CaSO₄. It is not two waters; gypsum (CaSO₄·2H₂O) is the one with two.

Drill 1 more on water of crystallization

Concept 3 of 3

Pigments and carbon black

Intuition

Pigments are the insoluble solids that give paint its colour. The bank lists three white pigments and slips in one non-pigment (silica). Carbon black is the black pigment, made by burning hydrocarbons with too little air.

Definition

The pigment facts:

White pigments: zinc oxide, white lead, and chalk (CaCO₃).
Silica is NOT a pigment (it is a filler/abrasive).
Carbon black is a black pigment made by the incomplete combustion of hydrocarbons (burning in a limited supply of air).

Substance	Pigment?	Note
Zinc oxide	Yes (white)	Common white pigment
White lead	Yes (white)	Traditional white pigment
Chalk (CaCO₃)	Yes (white)	Cheap white pigment/filler
Silica	No	A filler/abrasive, not a pigment Of zinc oxide, chalk, white lead and silica, the odd one out (NOT a pigment) is silica.
Carbon black	Yes (black)	Made by incomplete combustion of hydrocarbons

Practice this concept3 quick reps

Practice — Level 1 (3 reps)

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

1.
Which of zinc oxide, chalk, white lead and silica is NOT a pigment?
2.
How is carbon black obtained?
3.
Name a common white pigment.

From the bank · past-year question

Example 3Carbon and Its CompoundsMODERATE

Which one of the following is

\textbf{\text{not}}

a pigment?

[Q88 · Apr · 2022]

Drill 1 more on pigments and carbon black

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 names, formulas and uses6 rows

Common name	Chemical name / formula	Use or identity
Washing soda	Na₂CO₃·10H₂O	Cleaning, water softening
Baking soda	NaHCO₃	Baking, antacid
Dry ice	Solid CO₂	Refrigerant — sublimes, no liquid Dry ice is solid carbon dioxide, NOT frozen water.
Chalk / Marble	CaCO₃	Building, blackboard chalk
Vinegar	Acetic (ethanoic) acid	Food preservative, flavouring
Silica gel	SiO₂ (hydrated)	Desiccant — absorbs moisture

Water of crystallization4 rows

Salt	Formula	Water molecules
Blue vitriol (copper sulphate)	CuSO₄·5H₂O	5
Washing soda	Na₂CO₃·10H₂O	10
Gypsum	CaSO₄·2H₂O	2
Plaster of Paris	(CaSO₄)₂·H₂O	1 (shared by two CaSO₄ units) Plaster of Paris has ONE water of crystallization per TWO formula units of CaSO₄ — i.e. CaSO₄·½H₂O.

Pigments and carbon black5 rows

Substance	Pigment?	Note
Zinc oxide	Yes (white)	Common white pigment
White lead	Yes (white)	Traditional white pigment
Chalk (CaCO₃)	Yes (white)	Cheap white pigment/filler
Silica	No	A filler/abrasive, not a pigment Of zinc oxide, chalk, white lead and silica, the odd one out (NOT a pigment) is silica.
Carbon black	Yes (black)	Made by incomplete combustion of hydrocarbons

Watch out for (2)

Dry ice is CO₂, not ice
→ Common names, formulas and uses
Plaster of Paris = half a water per CaSO₄
→ Water of crystallization

Mastery check — 5 interleaved questions

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

Example 1Carbon and Its CompoundsEASY

Which one of the following is the best example of desiccant?

[Q147 · Apr · 2020]

Example 2Carbon and Its CompoundsMODERATE

Which one of the following is the number of water molecules that share with two formula unit

\text{CaSO}_{4}

in plaster of Paris?

[Q84 · Apr · 2018]

Example 3Carbon and Its CompoundsMODERATE

How is carbon black obtained?

[Q85 · Apr · 2018]

Example 4Carbon and Its CompoundsEASY

The chemical name of baking soda is

[Q126 · Apr · 2017]

Example 5Carbon and Its CompoundsEASY

Vinegar is also known as

[Q73 · Apr · 2020]

Drill every past-year question on this subtopic

10 questions from the bank — paginated, with cart and Word-export support.

Drill the 10 questions