StopLearnStopLearnCONTENT
Carbon (IV) Oxide
⦁ Formation/Preparation of Carbon (IV) Oxide (CO2)
⦁ Laboratory Preparation of CO2 Gas
⦁ Physical and Chemical Properties of CO2(g)
⦁ Uses of CO2
⦁ Advantages of Dry Ice Over Popular Ice
Carbon (II) Oxide
⦁ Laboratory Preparation of CO [in the fume cupboard]
⦁ Physical Properties of CO
⦁ Chemical Properties and Uses of CO
⦁ Synthetic Gas
⦁ Separation of the Constituents of Producer Gas and Water
Trioxocarbonates
⦁ Preparation of Metallic Trioxocarbonates
⦁ Properties of Salts
⦁ Trioxocarbonate (IV) Acid
⦁ Uses of Trioxocarbonate (IV) Salts
⦁ Chemical Tests for CO32- Salts
Carbon (IV) Oxide
Formation/Preparation of Carbon (IV) Oxide (CO2)
In excess air, there is complete combustion; carbon (iv) oxide is produced but in the limited supply of air carbon normally reacts with oxygen to produce carbon (ii) oxide. The equation of reaction is given below for the two reactions.
C(s)+ CO2(g) + heat (sufficient supply of air)
2C(s) + 2CO(g) + heat (limited supply of air)
Other methods of preparation of CO2 are:
1. CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
2. The decomposition of trioxocarbonates (IV) salts [except those of Sodium and Potassium] or hydrogen trioxcarbonate(IV) salts, by strong heat e.g
CaCO3(s) → CaO(s) + CO2
2NaHCO3(s) → Na2CO3(s) + H2O +CO2(g)
3. Action of dilute mineral acid on trioxocarbonate (IV) or hydrogentrioxocarbonate (IV) salt e.g.
Na2CO3(s) + 2HCl(aq) → 2 NaCl(aq) + H2O(l) + CO2(g)
KHCO3(s) + HNO3(aq) → KNO3(aq) + H2O(l) + 2CO2(g)
4. The fermentation of glucose by enzyme (zymase)
C6H12O6(ag) → 2C2H5OH(aq) + 2CO2(g)
Laboratory Preparation of CO2 Gas
The equation for the reaction is given as shown below:
CaCO3(s) + HCl(aq) → CaCl2(aq) + H2O + CO2(g)
Pure and dry CO2 is obtained by passing the gas through a solution of potassium hydrogentrioxocarbonate(IV) [KHCO3] to remove the acid impurities, hydrogen chloride and then, through conc. (or fused CaCl2 to dry the gas. It is then collected by downwards delivery, being denser than air as in the diagram above.
Physical Properties of CO2(g)
⦁ It is a colourless and odourless gas.
⦁ It does not support combustion
⦁ It is heavier or denser than air.
⦁ It is easily liquefied at low temperature with pressure higher than 5 atmospheres.
Chemical Properties of CO2(g)
1. It dissolves in water to give trioxocarbonate(IV) acid, H2CO3(aq)
H2O + CO2 → H2CO3(aq) ⇌ 2H+ + CO32-(aq)
∴ CO2 is an acid anhydride of H2CO3
2. It turns damp blue litmus paper red
3. It neutralizes the base [NaOH, KOH] to give salt and water only.
CO2 + 2NaOH(aq) → Na2CO3(aq) + H2O
When a large excess of the gas is used an acid salt is formed as shown in the equation above;
Na2CO3(aq) + H2O + CO2(ag) → 2NaHCO3(aq)
4. It acts as an oxidizing agents as shown in the reaction below.
(a) C(s) + CO2(g) → 2CO2(g)
(b) 2Mg(s) + CO2(g) → 2MgO(s) + C(s)
In this reaction, magnesium is oxidized to its oxide while CO2 is reduced to carbon.
5. It reacts with lime water to form Ca(OH)2, the equation is
CO2(g) + Ca(OH)2 → CaCO3(s) + H2O(l)
When it lasted for long inside lime water Ca(OH)2, the equation is
CaCO3(s) + H2O(l) + CO2(g) → Ca(HCO3)2(aq) colourless
These equations above are the laboratory chemical test for the presence of CO2 gas.
Uses of CO2
⦁ It is used in fire extinguishers because it is heavier than air and it does not support combustion.
⦁ It is used in the production of aerated drinks such as Coca-Cola, 7-Up and Pepsi-Cola.
⦁ It is used as effervescence in certain health salts such as Andrew Liver salt or Epson salt.
⦁ It is mixed with tartaric acid and corn starch to form baking powder (NaHCO3); causing bread to rise.
⦁ It is used in the production of Na2CO3 by Solvay process.
⦁ It is necessary for photosynthesis. The dissolved CO2 gas in sea-water provides sea plants with food for photosynthesis.
⦁ Solid CO2 is called Dry ice. It is used as a refrigerant in preserving food stuff. It is used as a coolant in nuclear reactor. It is called dry ice because it sublimes readily, without forming a liquid.
Advantages of Dry Ice Over Popular Ice
Dry ice produces a greater cooling effect than an equal mass of the common ice [ice block], because dry ice can provide a temperature of -790C [194k].
Again, dry ice on warming sublimes [changes from solid to gas] without leaving any liquid; unlike ice which melts to produce water.
CAUTION: Never handle solid CO2, dry ice, with bare hands; it causes painful blisters similar to those caused by hot objects.
EVALUATION
⦁ List the two reactants for the laboratory preparation of carbon(IV) oxide
⦁ Draw a labelled diagram for the laboratory preparation of dry sample of Carbon(IV) oxide.
⦁ Describe the laboratory test for CO2
⦁ Describe what will happen when CO2 is passed into water Ca(OH)2(aq) for a while then in excess
Carbon (II) Oxide
Laboratory Preparation of CO [in the fume cupboard]
Three methods can be used to prepare CO in the lab and they are as follows:
1. Ethanedioc acid crystals, [H2C2O4.2H2O]
decomposed
H2C2O2.2H2O(s) → 3H2O(l) + CO(g) + CO2(g)
Note: That conc. H2SO4 is a drying agent. It is there to remove the elements of water while KOH removes CO2(g)
CO2(g) + 2KOH(aq) → K2CO3(aq) + H2O(l)
2(a). Sodium Methanoate crystals
2HCOONa(s) + H2SO4(aq) → Na2SO4(aq) + 2H2O + 2CO(g)
2(b). Methannoic acid
HCOOH(I) H2SO4−H2O → CO(g) + CO2(g)
Show that H2SO4−H2O removes water, a dehydrating agent
3. Reduction of CO2(g) to CO as shown below
CO2(g) + C(s) → 2CO(g)
Physical Properties of CO
⦁ It is colourless, odourless and tasteless gas.
⦁ It is slightly lighter than air.
⦁ It is only slightly soluble in water, but insoluble in alkalis.
⦁ It is soluble in ammoniacal solution of copper(I) chloride.
⦁ It is a poisonous gas, hence, prepared in fume cupboard.
⦁ It is a neutral gas therefore it does not have any action on the litmus paper.
Chemical Properties and Uses of CO
1. It is used as fuel because it supports combustion.
2. It is a useful reducing agent because it is readily reduced to CO2(g) e.g.
(i) CO(g) + H2O → CO2(g) + H2(g)
(ii) CO(g) + CuO(s) → Cu(s) + CO2(g)
(iii) 3CO(g) + Fe2O3(s) → 2Fe(s) + 3 CO2(g)
(iv) CO(g) + PbO(s) → Pb(s) + CO2(g)
Note: The product of combustion or oxidation of CO is CO2; confirmed by its ability to turn lime water milky.
3. Ni(s) + 4CO(g) → Ni(CO)4(s)
At 1800C, nickel carbonyl decomposes to give carbon(II) oxide
Ni(CO)4(s) → Ni(s) + 4CO(g)
Ni(CO)4(s) nickel carbonyl
4. It combines with chlorine, using finely divided carbon as catalyst to form carbonyl chloride, COCl2[Phosgene]; a poisonous liquid. CO(g) + Cl2(g) → COCl2
Synthetic Gas
Like water gas, synthetic gas is a mixture of CO and hydrogen. It is obtained by passing natural gas [Methane] over steam or air in the presence of Nickels as the catalysts to give a mixture of CO and hydrogen
Ni.900oC
CH2(g) + H2O(g) → CO(g) + 3H2(g)
Ni.900oC
2CH4(g) + O2(g) → 2Co(g) + 4H2(g)
Separation of the Constituents of Producer Gas and Water
Producer gas is a mixture of CO and Nitrogen, while water gas is a mixture of CO and hydrogen.
Note: A fuel is any substance that burns in air or oxygen to produce heat and light. Producer gas and water gas are examples of gaseous fuels. Examples of solid fuels are wood, coal and coke
⦁ Liquid fuels e.g. producer gas, kerosene, alcohol or methylated spirit.
⦁ Gaseous fuels- e.g. producer gas, water gas, coal gas, natural gas paraffin gas and synthetic gas.
⦁ Human fuels e.g. food items in the form of fat and oil, protein, starch and sugar
⦁ Atomic fuel e.g. uranium
EVALUATION
⦁ Describe 2 methods of laboratory preparation of CO(g)
⦁ What is meant by fuel?
⦁ State the components of each of the following (a) water gas (b) Producer gas (c) coal gas (d) synthesis gas.
Trioxocarbonates
Preparation of Metallic Trioxocarbonates
All trioxocarbonate (IV) salts are insoluble in water except soluble. Hence, they are prepared by double decomposition method, using aqueous Na2CO3 e.g.
Na2CO3(aq) + CuSO4(aq) → CuCO3(s) + Na2SO4(aq)
Na2CO3(aq) + ZnCl2(aq) → ZnCO3(s) + 2NaCl(aq)
White
METHOD 2: Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
Properties of Salts
1. All trioxocarbonate (IV) salts are insoluble in water, except those of Na, K and NH4 which are soluble.
2. They dissolve in water to produce alkaline solutions. This is because they are salts of strong bases and weak acid, hence, they hydrolysed in water to produce alkaline solutions
e.g. K2CO3(s) + 2H2O → 2KOH(aq) + H2CO3(aq)
3. All trioxocarbonate(IV) salts except those of potassium and Sodium, decompose on heating, to liberate CO2(g).
e.g. ZnCO3(s) → ZnO(s) + CO2(g)
(NH4)2CO3(s) → 2NH3(g) + H2O(g) + CO2(g)
Note: Na2CO3 and K2CO3 are not affected by heating, to liberate carbon(IV) oxide e.g.
ZnCO3(s) + 2HCl(aq) → ZnCl2(aq) + H2O(l) + CO2(g)
Ionically: CO3(s)2-+ 2H+(aq) → H2O(l) + CO2(g)
Trioxocarbonate (IV) Acid
Trioxocarbonate (IV) [carbonic acid], H2 CO3 is a very weak diabasic acid. It is obtained when carbon (IV) oxide dissolves in water. It is unsuitable; hence never isolated.
CO2(g) + H2O ⇌ H2CO3(aq ⇌ 2H+(aq) + CO2-3(aq)
The acid forms both the normal and acid salts; i.e the acid ionizes into two stages;
1. H2CO3(aq) ⇌ H2CO3(aq) ⇌ H+(aq) + HCO–3(aq)
2. HCO–3(aq) ⇌ H+(aq) + CO2-3(aq)
Uses of Trioxocarbonate (IV) Salts
⦁ Na2CO3 is used in softening hard water, in making soap and glass, and as an alkali in acid-base titration.
⦁ CaCO3 is used in making quick lime, cement and glass; in agriculture [in liming the soil – to reduce acidity]
Chemical Tests for CO32- Salts
Test on liquid on Solid (dry test) …………… (a)
Small solid sample of salt is put in a test tube and few drops of dilute hydrochloric acid was added. Effervescence occur, then an odourless colourless gas was given off which in turn moist blue litmus paper slightly red and turns lime water. Gas is CO2(g)
Test (wet test) ………….. (b)
Barium chloride solution was added to few drops of solution of salt in test tube. A white precipitate was formed
CO2-3(ag) + BaCl2(aq) → BaCO3(s) + 2Cl–(aq)
The precipitate is soluble in dilute HCl, to give a colourless solution.
BaCO3(s)+ 2HCl(aq) → BaCl2(aq)+ H2CO3(aq)
EVALUATION
⦁ Describe the laboratory preparation of metallic trioxocarbonate (IV) salts
⦁ List two properties of trioxocarbonate (IV) salts
⦁ Give one method for preparation of trioxocarbonate (IV) acid
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