Amorphous Carbon - Wood Charcoal

Wood charcoal is obtained by the destructive distillation of wood. The chief products formed are wood charcoal, wood tar, pyroligneous acid and wood gas (Fig.10.6).

Wood charcoal is black, porous, brittle and soft. Though denser than water it can float on water, as it contains plenty of air bubbles trapped in the pores.

However, if wood charcoal is heated strongly, most of the air gets expelled and then if it is placed in water, it will sink (Fig.10.7).

Wood charcoal can absorb large volumes of gases onto its surface. Wood charcoal, when heated in steam to 900^oC, becomes activated charcoal. It can also be obtained by the destructive distillation of coconut shells. Activated charcoal has a much higher adsorption capacity. It is therefore used in purification of substances. It adsorbs impurities on its active surface from an impure substance so as to make it pure. It works very well especially for absorbing gases.

Experiment 2

The following experiment shows this property of adsorption (Fig.10.8).

Place a jar of dry ammonia over mercury. Adjust the levels of mercury inside and outside the bell jar till they are equal. Carefully, push in a large piece of charcoal, preferably, activated charcoal. You will notice that the level of mercury slowly rises inside the gas jar. This shows that charcoal adsorbs certain gases like ammonia.

Properties of Wood

Charcoal

• Charcoal is not a conductor of electricity.

• It burns in air or oxygen to form carbon dioxide. If the supply of air is limited, it forms carbon monoxide.

• When vapours of sulphur are passed over red-hot wood charcoal, they combine to form carbon disulphide (Fig.10.9).

• It reduces metallic oxide to the respective metals.

You can conduct the following experiment to show the reducing property of wood charcoal.

Experiment 3

Take a large block of charcoal. Make a cavity with a pointed knife, and place lead monoxide powder in the cavity. With the help of a blowpipe, blow a bunsen flame into the cavity. Charcoal reduces lead monoxide to a molten bead of lead. By plunging the charcoal block carefully in cold water, the molten lead solidifies and forms into a small granule of lead (Fig.10.10).

Similarly, it can reduce iron oxide to iron

• When steam is passed over red-hot wood charcoal, the two react to form water gas.

• Red-hot wood charcoal coverts carbon dioxide to carbon monoxide.

The uses of wood charcoal are:

• Wood charcoal is mostly used as a fuel as it catches fire easily.

• It is used in gas masks as an adsorbent.

• It is also used as a decolourising agent for sugar, oils, alcohol, petroleum products, etc.

• It is used in gun powder which is a mixture of charcoal powder, potassium nitrate and sulphur.