Classwork Series and Exercises {Chemistry – SS1}: Carbon(II)Oxide

Chemistry SS 1 Week 5

Topic: Carbon (II) Oxide

Introduction

In carbon (II) oxide, also known as carbon monoxide, exhibits oxidation state of +2. It is the choking gas produced during the incomplete combustion of gasoline in car engines. Carbon monoxide is a colourless, odourless, and tasteless gas that is slightly less dense than air.

Laboratory Preparation of Carbon (II) Oxide

Carbon (II) oxide (carbon monoxide), CO, is prepared in the laboratory by dehydrating methanoic acid (formic acid), HCOOH or ethanedioic (oxalic) acid and passing carbon(IV) oxide, CO₂, through red-hot carbon.

Dehydration

Methanoic acid, COOH, dehydrated in the presence of a dehydrating agent, concentrated tetraoxosulphate(VI) acid, H₂SO₄.

HCOOH(l) + conc. H₂SO₄ → CO(g) + H₂O(g)

Ethanedioic acid is heated warmly with concentrated tetraoxosulphate(VI) acid to form a gaseous mixture containing equal volume of carbon(II) oxide and carbon(IV) oxide. The mixture is passed through concentrated sodium hydroxide to separate the carbon(IV) oxide, thus forming carbon(II) oxide.

Large quantity of carbon(II) oxide is produced by incomplete combustion of carbon compounds like petrol. The octane, C₈H₁₈, component of petrol burns in the presence of oxygen to liberate water and form large quantity of carbon(II) oxide.

2C₈H₁₈(l) + 17O₂(g) → 16CO(g) + 18H₂O(l)

Reduction

Carbon(IV) oxide is prepared in the laboratory through the reaction of marble chips with dilute hydrochloric acid. The carbon(IV) oxide is then passed through strongly heated charcoal where it is mostly reduced to carbon(II) oxide.

CO(g) + CO₂(g) → 2CO(g)

But the CO gas is further passed through concentrated sodium hydroxide to remove accompanying carbon(IV) oxide impurities. Finally, the pure carbon (II) oxide is collected over water.

Physical properties of carbon monoxide

• Carbon monoxide is colourless, almost odourless and tasteless gas.
• It is very slightly lighter than air.
• Vapour Density is 14 [fusion_builder_container hundred_percent=”yes” overflow=”visible”][fusion_builder_row][fusion_builder_column type=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none”][Vapour density of air =14.4].
• Carbon monoxide is only very slightly soluble in water. 100 volumes of water can dissolve only 3.5 volumes of the gas at S.T.P
• This is a highly poisonous gas. Air containing even less than 1% of carbon monoxide, can be fatal, if breathed in for about 10 to 15 minutes.

Chemical Properties of Carbon (II) Oxide

The chemical properties of carbon (II) oxide has to do with its combination reactions and its reducing properties as presented below:

• Combination reaction with oxygen — Carbon(II) oxide combines with oxygen by burning in air with a faint blue flame to form carbon(IV) oxide,

2CO(g) + O₂(g) → 2CO₂(g)

• Combination reaction with haemoglobin — Carbon(II) oxide combines with haemoglobin, Hb, in the red blood cells to form carboxyhaemoglobin, COHb.

CO + Hb → COHb

This reaction is responsible for the poisonous nature of carbon(II) oxide as the haemoglobin is converted to a stable carboxyhaemoglobin that cannot transport oxygen across the body.

• Carbon(II) oxide as a reducing agent: Carbon(II) oxide is a strong reducing agent that is oxidized to carbon(IV) oxide in the presence of compounds like metallic oxides, steam and iodine(V) oxide
  It reduces lead(II) oxide, PbO, to lead metal, Pb.PbO(s) + CO(g) → Pb(s) + CO₂(g)It reduces steam to hydrogen gas, H₂.H₂O(g) + CO(g) → H₂(g) + CO₂(g)and also reduces iodine(V) oxide to iodine, I₂,

  I₂O₅(s) + 5CO(g) → I₂(s) + 5CO₂(g

Uses of carbon(II) oxide

• 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.
• It is used as a reducing agent in the extraction of metals. Carbon monoxide reduces the metal oxides to metals. Usually coke is used to generate this gas. In this process coke combines with oxygen to form carbon dioxide, which gets reduced to carbon monoxide due to the lack of oxygen.
• Carbon monoxide is used in the manufacture of methyl alcohol, sodium formate, phosgene, etc.

CARBON (IV) OXIDE

Carbon (IV) Oxide, also known as Carbon Dioxide (chemical formula CO2), is a colourless, odourless gas vital to life on Earth. Carbon dioxide, CO₂, is one of two oxides of the element carbon and is the main product oxide of carbon formed from the combustion of hydrocarbon fuels. Carbon dioxide is present in the atmosphere and is produced by respiration and combustion. However it has a short time in this phase as it is consumed by plants during photosynthesis

Preparation of Carbon Dioxide

Carbon dioxide is prepared

• By treating any metallic carbonate with dilute mineral acids

CaCO3   +   2 HCl   ==>   CaCl2   +   H2O   +   CO2

• By heating carbonates of metals other than alkali metals

MgCO3          ==>   MgO   +   CO2

Physical Properties of Carbon (IV) oxide

Some physical properties of carbon dioxide are:

–          Colourless

–          Odourless

–          Soluble in water, ethanol and acetone

–          Melting point is -78°C

–          Boiling Point is -57°C

Chemical properties

• When bubbled into water it dissolves slightly and some of the carbon dioxide reacts, forming a solution of a weak acid carbonic acid which shows a pH of 5.

H₂O(i) + CO₂(g)   H₂CO₃(aq)

• It supports the combustion of only strongly burning substances such as magnesium. Magnesium metal decomposes the carbon dioxide to provide oxygen for its continued burning in the gas.

2Mg(s) + CO₂(g)   2MgO (s) + C(s)

This reaction is a reduction-oxidation (redox) process in that magnesium is oxidised as carbon dioxide is reduced

• When carbon dioxide is bubbled through lime water (calcium hydroxide solution), a white precipitate (calcium carbonate) is formed. This reaction is used as a test to show that a gas is carbon dioxide.

Ca(OH)₂ (aq) + CO₂(g)  CaCO₃ (s) + H₂O (l).

If carbon dioxide is bubbled through the solution continuously then it will eventually become clear. This is because of formation of soluble calcium hydrogen carbonate solution.
CaCO₃ (s) + H₂O (l) + CO₂ (g)  Ca(HCO₃)₂ (aq)

• Carbon dioxide reacts with strong alkalis, such as sodium hydroxide, to form carbonates. A solution of sodium hydroxide can be used to absorb carbon dioxide from the air. If excess carbon dioxide is bubbled through a solution of sodium hydroxide then a white precipitate of sodium hydrogen carbonate may be obtained.

2NaOH (aq) + CO₂ (g)  Na₂CO₃ (aq) + H2O (l)

Na₂CO₃ (aq) + H₂O (l) + CO₂ (g)  2NaHCO₃ (s)

Uses of carbon dioxide

Carbon dioxide has some important uses, these are:

• To make ‘fizzy’ (carbonated) drinks like Coca-Cola, Pepsi-Cola etc. Carbon dioxide dissolves in water under pressure. Carbon dioxide gives taste to the soft drink

Soft drink

• As dry ice in refrigerators. Solid carbon dioxide sublimes and so it is used as a refrigerant for ice cream meat and soft fruits. It is used for this purpose because it is colder than ice and it sublimes at -78 ^oC, and so it does not pass through a potentially damaging liquid state.
• It is used in fire extinguishers; being denser than air, it blankets the fire and prevents oxygen from reaching it hence putting the fire out.

Fire extinguisher and that of it being used to put out fire

• It is produced insitu by baking powder, and also in health salts. Baking powder consists of a dry mixture of sodium hydrogen carbonate and a solid acid such as tartaric or citric acid. Reaction only takes place when water is added, when the acid reacts with the hydrogen carbonate to form carbon dioxide that makes the dough rise. A similar principle is used in health salts like Andrews Liver Salt. In health salts, carbon dioxide evolved helps in relieving indigestion or constipation
• Carbon dioxide gas is used for transferring heat in some nuclear stations in atomic reactors.

 

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