Carbon monoxide (CO) is a colorless, odorless, and highly poisonous gas. It is formed during the incomplete combustion of carbon or carbon-containing compounds.

Carbon monoxide can be prepared in the laboratory by the reaction of concentrated sulfuric acid on formic acid(methanoic acid), or by heating oxalic acid (ethanedioc acid) with concentrated sulfuric acid. The concentrated sulphuric acid aerves as a dehydrating agent:

1. Step 1: Take oxalic acid (H₂C₂O₄) in a flask.
2. Step 2: Add concentrated H₂SO₄ carefully. The acid dehydrates the oxalic acid to produce CO and CO₂:

H₂C₂O₄ → CO₂ + CO + H₂O (in presence of conc. H₂SO₄)

3. Step 3: Pass the mixture of gases through a concentrated NaOH solution to remove CO₂; the remaining gas is CO.
4. Step 4: Collect the gas over water or by downward displacement of air.

• Colorless and odorless gas.
• Slightly lighter than air and insoluble in water.
• Non-flammable but burns in air with a blue flame to give CO₂.
• Highly toxic even at low concentrations.
• It is neutral to litmus paper

• Reaction with Oxygen:
  • Burns in oxygen to produce carbon dioxide:

  2CO + O₂ → 2CO₂

• Reaction with Metals:
  • Reduces metal oxides to metals at high temperatures. This makes it a good reducing agent:

  Fe₂O₃ + 3CO → 2Fe + 3CO₂

• Reaction with Water:
  • Under high pressure and temperature, CO reacts with steam in the water-gas shift reaction:

  CO + H₂O ⇌ CO₂ + H₂

• Reaction with Hemoglobin:
  • CO combines with hemoglobin in the blood to form carboxyhemoglobin (HbCO), which prevents oxygen transport and causes suffocation:

  Hb + CO → HbCO

Carbon monoxide can be identified by its ability to reduce certain metal oxides and by the color of its flame when burned in air.

1. Test: CO burns with a characteristic blue flame to form carbon dioxide which turns lime water milky.

2CO + O₂ → 2CO₂

Observation: The gas burns with a blue flame — confirms CO presence.

2. Reduction of Hot Copper(II) Oxide:
• When CO is passed over hot copper(II) oxide (CuO), the black solid is reduced to red metallic copper while CO is oxidized to CO₂:

CuO + CO → Cu + CO₂

• Observation: The black CuO changes to reddish-brown Cu and lime water turns milky (due to CO₂ formation).

• Used as a reducing agent in metallurgy (extraction of metals from oxides).
• Used in the manufacture of chemicals like methanol.
• Used in fuel gas mixtures (producer gas, water gas) for industrial heating.