10- Nitric Acid

Nitric acid is also known as

aqua fortis

Laboratory preparation

Laboratory preparation using Potassium nitrate & Sodium Nitrate

• KNO₃ + H₂SO₄ (<200 C) → KHSO₄ + HNO₃

• NaNO₃ + H₂SO₄ (<200 C) → NaHSO₄ + HNO₃

Why is the acid obtained slightly yellow

Due to dissolution of reddish brown coloured Nitrogen dioxide gas in tthe acid

How is the yellow colour removed:

Two ways:

• if dry air or CO₂ is bubbled through the yellow acid, the latter turns colourless because it drives out NO₂

• By addition of excess of water, Nitrogen di oxide gas dissolves in water and thus the yellow colour of the acid is removed

Give 3 precautions

• All glass apparatus is used because nitric acid vapours attack rubber and cork

• HCl is not used because its volatile and hence nitric acid vapours will carry HCl vapours

• The temperature of the reaction should not exceed 200 C

What happens if temperature exceeds 200 C

• glass may crack

• decomposition of nitric acid can occur

• fuel is wasted

Catalyst used in Ostwald process

Platinum

Guve reaction for Ostwald process

What happens if pure nitric acid is left in sunlight

4HNO₃ (Sunlight) → 4NO₂ + 2H₂O + O₂

WHy is nitric acid stored in bottle turns yellow

The colour is due to dissolved NO₂ in HNO₃. To avoid the decomposition, nitric acid is generally stored in coloured bottles

How does nitric acid effects litmus paper

Blue → Red

Reaction: Action on Non metals

Two Reactions:

• C + 4HNO₃ → CO₂ + 2H₂O + 4NO₂

• S + 6HNO₃ → H₂SO₄ + 2H₂O + 6NO₃

Reaction: Action of metals

• Cold dilute nitric acid: : 3Cu + 8HNO₃ → 3Cu(NO₃)₂ + 4H₂O + 2NO

• Concentrated Nitric Acid(Hot dilute): Cu + 4HNO₃ → Cu(NO₃)₂ + 2H₂O + 2NO₂

What type of acid is dilute nitric acid and why?

Typical acid because it is a powerful oxidising agent

Reaction of nitric acid with aqua regia

HNO₃ + 3HCl → NOCl + 2H₂O + 2[Cl]