Carbon & its compound

Carbon and its compounds

Position:

Carbon belongs to IVA group along with 4 other elements (Silicon, Germanium, Tin & Lead). Electronic configuration of carbon is

1s², 2s², 2p²

It is a p-block element.

Allotropes of carbon

Metal exist in the different form in nature which is different in physical properties but similar in chemical properties. Such phenomenon of existence in nature is known as allotropy.

The different allotropic forms of carbon are

1. Crystalline (Diamond, Graphite, Fullerene)
2. Amorphous (Coal, Charcoal, Coke)

Diamond

• A pure crystalline form of carbon.
• Hardest natural substance.
• Density 3.51 and refractive index 2.45.
• Non-conductor of heat and electricity.
• Changes into graphite when heated over 1800°C.

Structure

It is sp³ hybridized carbon atom covalently bonded to other 4 carbon atom to form a regular tetrahedron with a bond angle of 109°28'. All the carbon atoms are covalently bonded throughout the crystal which makes it so hard. Since the carbon-carbon bond is uniform and short, the whole crystal becomes strong (Bond length = 1.54 Aº & 1Aº= 10^-8). Since, all four electron carbon atom are used to form the covalent bond, no any free electron is left so it is unable to conduct electricity.

Uses

• As a jewelry
• Black diamond help to cut glass and polish other diamond.

Graphite

• Known as black lead or plumbago.
• Soft, grey, crystalline substance which can be found naturally & can be prepared artificially.
• Marks paper black (so used I pencil & known as black lead).

Structure

It is sp² hybridized carbon atom bonded to other 3 carbon atom to hexagonal network with a bond angle of 120°. Layers of graphite are bonded with weak Vanderwall force. Since, one layer of graphite slip over another, it is soft & slippery and hence also used as the lubricant. Since graphite has one free electron, it is able to conduct electricity.

Carbon-carbon bond length = 1.42 Aº & 1Aº= 10^-6 cm

Bond angle =120°

Successive layer = 3.40 Aº

Uses

• Good conductor of electricity so used to make the electrode.
• Used for making graphite crucial that can hold high temperature.
• Since it is slippery, it can be used to make lubricant & as an additive to motor oil.

Fullerene

It is latest discovered crystalline allotrope of carbon. It is nearly spherical containing 60 atoms of carbon covalently bonded to each other & looks like the soccer ball and called bulky ball & cell known as “Buck Minister Fullerene”. It has 12 pentagonal and 20 hexagonal forces and it shows superconductivity.

Amorphous Allotropes of Carbon

Coal:It is obtained by slow decomposition of wood or green matter under the effect of heat, pressure& limited supply of air. It helps to manufacture producer gas (CO + N₂) & water gas (CO + H₂).

Coke:It is the purest amorphous greyish black liquid form of carbon obtained by destructive distillation of coal. It can be used as the reductant in metallurgy.

Charcoal:It is obtained by destructive distillation of wood, sugar, bone etc. It is the porous form of carbon. It can be used to absorb toxic gas & purify liquid.

Types of Charcoal

1. Wood charcoal: obtained by destructive distillation of wood in the limited supply of air.
2. Animal charcoal: obtained by destructive distillation of bone.
3. Sugar charcoal: obtained by heating of sugar in the absence of air or by the addition of concentrated sulphuric acid (H₂SO₄) in sugar.
4. Lamp black: obtained by burning oil in the limited supply of air. Used for making shoe polish, ink etc.

Laboratory preparation of carbon monoxide (CO)

In the lab, carbon monoxide (CO) is prepared by heating oxalic acid crystal ((COOH)₂2H₂O) with concentrated sulphuric acid (H₂SO₄).

$$(COOH)_2⋅2H_2O+H_2SO_4\longrightarrow CO_2\uparrow+CO\uparrow+H_2SO_4⋅3H_2O$$

The gases are passed through the aqueous solution of caustic soda (NaOH) so that carbon dioxide (CO₂) is occupied & carbon monoxide (CO) is freely found.

Procedure

• Take few amount of oxalic acid in a round bottom flask.
• Use a cork to fix thistle funnel & delivery tube.
• Use the thistle funnel to pass concentrated H­₂SO₄ dropwise.
• Heat is passed & then carbon monoxide (CO) & carbon dioxide (CO₂) gas evolve out which pass on through caustic soda (NaOH) solution.
• The NaOH solution occupies the carbon dioxide (CO₂) gas & at last carbon monoxide (CO) is collected by downward displacement of water.

Physical properties

• Colorless gas with the slight smell.
• Lighter than air & soluble in air.
• Highly poisonous gas.

Chemical properties

• It is neutral (neither acidic nor basic in nature).
• It doesn’t support combustion but burns with blue flame & gives carbon dioxide.

$$2CO+O_2\longrightarrow2CO_2+Heat$$

• It reacts with hydrogen to form methanol (CH₃-OH).

$$CO+2H_2\longrightarrow CH_3-OH$$

• It reacts with chlorine to form phosgene (phosgene can be used as deadly weapon)

$$CO+Cl_2\longrightarrow COCl_2$$

• It reacts with caustic soda (NaOH) to form sodium formate (HCOONa).

$$CO+NaOH\longrightarrow HCOONa$$

• It combines with metals like iron, nickel, cobalt to form carbonyls.

$$Fe+5CO\longrightarrow Fe(CO)_5 (Iron\space carbonyl)$$

$$Ni+4CO\longrightarrow Ni(CO)_4 (Nickel\space carbonyl)$$

$$CO+4CO\longrightarrow CO(CO)_4 (Cobalt\space carbonyl)$$

• It reacts as the reductant. It reduces metals oxides into metal.

$$Fe_2O_3+3CO\longrightarrow 2Fe+3Co_2 (Ferric\space oxide\space to\space iron)$$

$$ZnO+CO\longrightarrow Zn+CO_2 (Zinc\space oxide\space to\space zinc)$$

Uses

• Used as fuel.
• Used to prepare weapon ie. Phosgene.
• Purification of nickel by Mond’s process is done with it’s application.

Dry Ice

The solid form of CO₂ is known as dry ice. It is called so because it is similar to ice but doesn’t wet cloth or paper when placed onto them.

Reference:

Bibliography

Pulse, Tracy. Introduction to chemistry. u.s.a: flex book, 2010.

Pathak, Sita Karki. The Text Book of Chemistry. kathmandu: Vidhyarthi Pustak Bhandar, 2012.