Compounds of Carbon
Carbon has a variable valency of 2 and 4, and as a result, produces two important kinds of oxides namely carbon monoxide and carbon dioxide. Both these oxides are gases at room temperature.
Carbon monoxide - Occurrence
Normally air does not contain any appreciable amount of carbon monoxide. However, air around volcanic regions may contain a negligible percentage of it. In urban and industrial areas, it may be present in traces due to the incomplete combustion of fuels in industry, as well as in automobiles. You may also find it in the presence of people who smoke, as it is present in traces in tobacco smoke. As a result, you may be exposed to this gas many times even if you are a non-smoker.
Preparation of Carbon Monoxide
Carbon monoxide was first prepared in the laboratory in 1776 by J.M.F. de Lassone, a French chemist. As carbon monoxide is extremely poisonous, its preparation should be carried out only in a fume chamber. Under no circumstances must the gas be inhaled or smelled.
Commercial Preparation of Carbon Monoxide
Carbon monoxide is commercially prepared by burning carbon in excess of oxygen, and then passing the carbon dioxide so formed, over white- hot carbon.
Physical Properties of Carbon Monoxide
Nature Carbon monoxide is colorless, almost odorless and tasteless gas.
Chemical Properties of Carbon Monoxide
Combustibility It is a combustible gas. It burns well in air or oxygen to form carbon dioxide. The formation of carbon dioxide is tested by passing it through a solution of lime water.
Tests for Carbon Monoxide
1. Carbon monoxide is colourless, neutral gas.
2. It burns in air or oxygen with a pale blue flame to form carbon dioxide.
Uses of Carbon Monoxide
Carbon monoxide is used as a fuel by itself, or in the form of producer gas (mixture of carbon monoxide and nitrogen), or water gas (mixture of carbon monoxide and hydrogen). It is also present in fuel gases like coal gas.
Physiological Action of Carbon Monoxide
Carbon monoxide is an extremely poisonous gas as a result of its physical properties, which add to the deadly nature of the gas. As the gas is almost odourless, its presence cannot be detected. Also its vapour density is almost equal to that of air. Hence it mixes easily with air. It neither goes up like ammonia nor goes down like chlorine.
Carbon Dioxide - Occurrence
Jan Baptista van Helmont discovered the presence of carbon dioxide in the year 1630.
Although the percentage of carbon dioxide in air is very small, it plays a vital role in nature. All the food that is produced on the earth is by photosynthesis, which employs carbon dioxide as the basic raw material.
Formation of Carbon Dioxide
By the combustion of carbon or carbonaceous materials
Laboratory Preparation of Carbon Dioxide
In the laboratory, carbon dioxide is usually prepared by the action of dilute hydrochloric acid on marble chips. Marble chips are taken in a round-bottomed flask.
Physical Properties of Carbon Dioxide
Density Carbon dioxide is heavier than air. Its vapour density is 22 (Vapour density of air = 14.4). Hence, it is 1.5 times denser than air. So it tends to move downwards. Certain caves and valleys, which contain carbon dioxide may be fatal to animals, as they get choked to death.
Physiological Action
It is not a poisonous gas. But death can occur in excess of carbon dioxide due to asphyxiation or choking, for lack of oxygen or air.
Chemical Properties of Carbon Dioxide
Nature : Carbon dioxide is slightly acidic. It turns blue litmus paper red. During rainy season, blue litmus paper kept open in the laboratory slowly turns red, due to the presence of carbon dioxide in air.
Tests for Carbon Dioxide
Carbon dioxide is a colourless and almost tasteless gas that puts off a flame.
Uses of Carbon Dioxide
In nature
a) Carbon dioxide is used in photosynthesis by green plants to produce carbohydrates.
b) To induce natural breathing.
Fire Extinguishers
There are 4 types of fire extinguishers available in the market. They are:
a) Soda-acid type
b) Foam type
c) Liquid carbon dioxide type and
d) Solid sodium hydrogen carbonate type.
Carbon Cycle
The cyclic changes that carbon undergoes in nature is referred to as the Carbon cycle. Carbon in the form of carbon dioxide gets added to the air and gets removed from the air constantly. This addition and subtraction is so well balanced that the percentage of carbon dioxide remains remarkable steady at 0.03 to 0.04.
Comparison Between Properties of Carbon monoxide and Carbon dioxide Gases
| Property | carbon monoxide (CO) | carbon dioxide(CO2) |
|---|---|---|
| Vapour density | Almost as dense as air: Vapour density = 14: (Vapour density of air 14.4) | 1.5 times as dense as air; Vapour density = 22 |
| Solubility | Almost insoluble in water even at high pressure | Fairly soluble in water. 1 volume of water dissolves one volume of the gas at 59°F; solubility increases drastically at higher pressures |
Quicklime (Calcium Oxide, CaO)
Preparation
Quicklime is prepared by the thermal decomposition of lime stone (marble, chalk or even sea shells).
Slaked Lime (Calcium Hydroxide)
Preparation
By treating quick lime with water calcium Hydroxide is obtained.
Summary
Carbon shows valencies 2 and 4, and forms two oxides - carbon monoxide (CO) and carbon dioxide (CO2).
