THE GAS THAT TURNS LIME MILKY WATER

The gas which turns lime water milky is: 

- Nitrogen dioxide

- Carbon monoxide

- Carbon dioxide

- Oxygen

Lime manufacture

From the earliest of times, lime has been made by heating limestone to high temperatures.

Production methods have evolved from heating limestone in open fires, to the use of brick lime kilns at the start of the 17th century, to today’s horizontal rotating kilns several metres in diameter and up to 100 metres in length.

These modern kilns operate at a temperature of about 1100-1200°C, allowing rapid conversion of limestone into lime.

CaCO3(s) limestone → CaO(s) lime + CO2(g) carbon dioxide

Lime’s chemical properties

Lime (calcium oxide) is a white solid with strongly basic properties.

The lime reacts readily with water to produce slaked lime, which is the chemical compound calcium hydroxide. A considerable amount of heat energy is released during this reaction.

CO2 is a colourless, odourless, incombustible gas. It is a product of cellular respiration and combustion and is an essential component in photosynthesis.

Important Points

Calcium hydroxide is sparingly soluble in water producing an alkaline solution known as limewater. When carbon dioxide gas is passed through or over limewater, it turns milky due to the formation of calcium carbonate.

CaO(s)

lime

+

H2O(l)

water

→

Ca(OH)2(s)

slaked lime

Ca(OH)2(s)

slaked lime

+

H2O(l)

water

→

Ca(OH)2(aq)

limewater

Ca(OH)2(aq)

limewater

+

CO2(g)

carbon dioxide

→

CaCO3(s)

calcium carbonate