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.
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
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
The same idea in a real exam question:
Example 1 · Carbon and Its Compounds · Common Carbon Compounds and Pigments
Dry ice is CO₂, not ice
Concept 2 of 3: Water of crystallization
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
The same idea in a real exam question:
Example 2 · Carbon and Its Compounds · Common Carbon Compounds and Pigments
Plaster of Paris = half a water per CaSO₄
Concept 3 of 3: Pigments and carbon black
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
The same idea in a real exam question:
Example 3 · Carbon and Its Compounds · Common Carbon Compounds and Pigments
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
Test yourself on Carbon and Its Compounds
15 past NDA questions from this chapter, timed at 15 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.