Chemistry Kenya
Carbon and some of its Compounds
Carbon and some of its Compounds
Carbon and some of its Compounds
Forms of carbon
Although carbon forms less than one percent of the earth’s crust by weight, it is the most interesting of all elements. This is because of the following reasons:
- All living things are made of carbon and its compounds.
- Over ¾ of the world’s power is obtained from carbon and its compounds.
- Over ¾ of all substances in the world are made of carbon.
Carbon is not commonly found in a free state. The free element is mainly found as graphite and diamond. Carbon occurs in a number of other forms, e.g. wood charcoal, animal charcoal, coke, soot (lampblack).
Carbon compounds are found in many naturally occurring substances such as coal, petroleum, wood, coal gas, natural gas, carbonates, shells, organic matter of all kinds, all living things, and occurs in the air to a small, but very important extent (0.03 – 0.04% by volume) as carbon dioxide. The carbohydrates, proteins and lipids in all living things contain carbon.
Pure carbon is found in the form of diamond in Tanzania (Mwadui), Sierra Leone, India, South Africa, Russia and South America; and impure carbon, as graphite, is found in Sri Lanka.
Diamond,graphite and charcoal: structure, physical properties and uses (relate uses to structure and physical properties)
Chemical properties of carbon
Combustion, reaction with acids and reducing action
Preparation and properties of Carbon (IV) oxide (carbon dioxide)(Relate methods of collection to the properties of the gas)
Carbon dioxide is one of the oxides of carbon. The gas is present in the air at a level of approximately 0.03% by volume. It is also found dissolved in water. The gas is one of the by-products of all decaying organic matter. Without carbon dioxide there is no life on earth. It is used by all plants in the process of photosynthesis and both plants and animals evolve carbon dioxide in respiration.
Laboratory preparation of carbon dioxide
Carbon dioxide is prepared in the laboratory by the action of dilute hydrochloride acid on marble (calcium carbonate).
When dilute hydrochloric acid is poured on marble chips, effervescence occurs. Dilute hydrochloric acid reacts with the marble chips to give calcium chloride, water and carbon dioxide.
CaCO3(s) + 2HCl(aq) → CaCl2(g) + H2O(l) + CO2(g)
Physical properties
- Carbon dioxide is a colourless and odourless gas.
- It is denser than air.
- When the gas is cooled to –78°C, it turns straight into the solid (it sublimes). Sublimation is the change of a gas straight into a solid or change of a solid straight into a gas. Solid carbon dioxide is called dry ice. It sublimes when it is heated or exposed to air.
- It has a melting point of –199°C and boiling point of –91.5°C.
- Carbon dioxide does not support combustion. This is why it is used in fire extinguishers.
Chemical properties
Reaction of carbon dioxide with lime water (Test for carbon dioxide)
When a little carbon dioxide gas is bubbled into lime water (calcium hydroxide solution), the solution turns milky. This is due to the formation of a white precipitate of insoluble calcium carbonate.
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
This is a confirmatory test for the presence of carbon dioxide. The test serves to distinguish carbon dioxide from any other gas.
When excess carbon dioxide is bubbled into the lime water, the white perceptible dissolves to form a clear solution of soluble calcium hydrogen carbonate: CaCO3(s) + H2O(l) + CO2(g) → Ca(HCO3)2(aq)
Barium hydroxide can also be used to test for carbon dioxide as it forms a precipitate of barium carbonate: Ba(OH)2(aq) + CO2(g) → BaCO3(s) + H2O(l)
Reaction of carbon dioxide with magnesium
When a burning magnesium ribbon is lowered into a gas jar containing carbon dioxide gas, it continues to burn for a short time with a spluttering flame. A white ash of magnesium oxide and black specks of carbon are formed. The black specks of carbon can be seen on the sides of the gas jar.
2Mg(s) + CO2(g) → 2MgO(s) + C(s)
This clearly shows that carbon dioxide contains carbon and oxygen.
Reaction of carbon dioxide with water
Carbon dioxide reacts with water to form a weak carbonic acid. When carbon dioxide is bubbled into water, it dissolves to form a weakly acidic solution of carbonic acid:
H2O(l) + CO2(g) ⇔ H2CO3(aq)
The solution turns a blue litmus paper pink. This indicates that the solution is slightly acidic and hence too weak to turn the blue litmus paper to red (as strong acids do). The solution has no effect on red litmus paper.
Reactions of the gas with water, calcium hydroxide and alkalis
Uses of carbon (IV) oxide (carbon dioxide)
Preparation and properties of Carbon (II) oxide (carbon monoxide)
Preparation of carbon(II)oxide (carbon monoxide)
Physical properties, chemical properties, combustion, reducing action, poisonous nature such as car exhausts fumes and charcoal fire. NOTE: Only theoretical treatment required because of its poisonous nature.
Carbonates and hydrogen carbonates
Action of heat and dilute acids on carbonates and hydrogen carbonates
Production and manufacture of sodium carbonate (Magadi Soda Company and solvay process). NOTE: Use simple schematic diagrams to illustrate solvay process.
Importance of carbon and its oxides
Carbon cycle
Soft drinks manufacturer
Fire extinguishers
The effects of Carbon(IV)oxide (carbon dioxide) and carbon(II)oxide (carbon monoxide) on the environment
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