Sulfur (S) — Atomic Number 16

Sulfur is a chemical element with the symbol S and atomic number 16. It is a bright yellow non-metal solid known since antiquity (biblical “brimstone”). It is the feedstock for sulfuric acid, the most produced chemical worldwide.

At a Glance

Chemical Properties

Key Reactions

1. Combustion: $\text{S}+{\text{O}}_2\to {\text{SO}}_2$ — burns with a blue flame, choking gas
2. With iron: $\text{Fe}+\text{S}\stackrel{\Delta }{\to }\text{FeS}$ (glows red, forms black solid)
3. SO₂ is acidic: ${\text{SO}}_2+{\text{H}}_2\text{O}\to {\text{H}}_2{\text{SO}}_3$

Characteristic Test

SO₂ turns acidified potassium dichromate(VI) from orange to green (reducing agent).

The Contact Process (Making Sulfuric Acid)

1. $\text{S}+{\text{O}}_2\to {\text{SO}}_2$ (burn sulfur)
2. $2{\text{SO}}_2+{\text{O}}_2\rightleftharpoons 2{\text{SO}}_3$ (V₂O₅ catalyst, 450 °C, 1–2 atm)
3. ${\text{SO}}_3+{\text{H}}_2{\text{SO}}_4\to {\text{H}}_2{\text{S}}_2{\text{O}}_7$ (oleum)
4. ${\text{H}}_2{\text{S}}_2{\text{O}}_7+{\text{H}}_2\text{O}\to 2{\text{H}}_2{\text{SO}}_4$

Compounds & Uses

• Vulcanisation of rubber
• Gunpowder (charcoal + sulfur + potassium nitrate)

Environmental Impact

Burning fossil fuels → SO₂ → acid rain. Damages buildings (dissolves limestone), acidifies lakes, harms forests.

IGCSE Essentials

1. Yellow solid, burns with blue flame
2. Contact Process: V₂O₅, 450 °C, 1–2 atm
3. SO₂ causes acid rain
4. Test for SO₂: potassium dichromate turns green

Sources

• Sulfur — Wikipedia
• Sulfur — Ptable.com