Oxide of Carbon

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In today’s class, we will be talking about the oxide of carbon. Enjoy the class!

OXIDE OF CARBON

CONTENT

• Carbon (iv) oxide
• Carbon (ii) oxide

CARBON (iv) OXIDE

The percentage composition of carbon (iv) oxide in the atmospheric air is about 0.03% by volume while in dissolved air is about 0.50% by volume.

Laboratory preparation

1. Carbon (iv) oxide is prepared in the laboratory by the action of dilute acids on a trioxocarbonate (iv) or a hydrogen trioxocarbonate (iv). Usually CaCO₃, in the form of marble chips, shells or ‘potash’; is used with hydrochloric acid or trioxonitrate (v) acid. The reaction between CaCO₃ and HCl can be carried out in Kipp’s apparatus.

CaCO_3(s)             +        2HCl_(aq)   →    CaCl_2(aq) + H₂O_(l) + CO_2(g)

NaHCO_3(aq)       +     HNO_3(aq)    →     NaNO_3(aq)   +  H₂O_(l)     +    CO_2(g)

2. It is also prepared by heating metallic trioxocarbonates (iv) [except those of Na and K], or the hydrogen trioxocarbonate (iv) of Na or K.

CuCO_3(s)      →   CuO_(s)     +       CO_2(g)

Note: If the gas is required dry, it is pass through potassium hydrogen trioxocarbonate (iv) solution first to remove any acid fumes, and then through a U-tube containing fused Calcium chloride to remove the water vapour. The dry gas is then collected by downward delivery as it is heavier than air.

Method of collection of gases

The method of collection of gases depends on its:

1. Density.
2. Solubility.

There is two methods of collecting gases:

(a) Downward delivery/upward displacement of air: This method is used for collecting gases that are denser than air e.g. CO₂, SO₂, H₂S, NO₂, Cl₂ and HCl etc.

(b) Upward delivery/downward displacement of air: This method is used for collecting gases that are less denser than air e.g. NH₃, H₂, N₂, methane and ethane.

INDUSTRIAL PREPARATION

CO₂ is obtained industrially as a by-product in fermentation processes and when limestone is heated to make quicklime.

PHYSICAL PROPERTIES

(1) CO₂ is a colourless, odourless gas with a sharp refreshing taste.

(2) It is about 1.5 times denser than air.

(3) It is soluble in water. At room temperature and standard pressure, water dissolves its own volume of the gas.

(4) It turns damp blue litmus paper pink because CO₂ dissolves in water to yield trioxocarbonate(iv)acid.

(5) On cooling, it readily liquefies and solidifies (-78⁰C) to form a white solid known as dry ice.

CHEMICAL PROPERTIES

1. Reaction with water: Carbon (iv) oxide is not very active chemically. It dissolves in water to form trioxocarbonate (iv) acid (Soda water). This is a weak, dibasic acid which ionizes slightly.

(a)  CO_2(g)             +     H₂O_(l)    →    H₂CO_3(aq)

(b)  H₂CO_3(aq)     +     H₂O_(l)    →      H₃O⁺_(aq)       +    HCO₃^–_(aq)

(c)  HCO₃^– _(aq)       +     H₂O_(l)         →     H₃O⁺_(aq)     +    CO₃^2-_(aq)

On heating, trioxocarbonate (iv) acid decomposes to form H₂O_(l) and CO_2(g).

2. Reaction with alkalis: It reacts directly with alkalis to yield trioxocarbonate (iv)

CO_2(g)     +  2NaOH_(aq)     →    Na₂CO_3(aq)       +       H₂O_(l)

Limited

Excess CO₂ reacts with alkalis to produce Hydrogen trioxocarbonate (iv) salt.

CO_2(g)       +  NaOH_(aq)     →    NaHCO_3(aq)

Excess.

3. Reaction with burning Na, K or Mg: CO₂ is reduced to carbon by burning Na, K or Mg.

CO_2(g)     +      2Mg_(s)    →    C_(s)      +       2MgO_(s)

Note: CO₂ does not support combustion.

4. Reaction with red hot carbon: CO₂ is reduced to CO If the gas is passed over red hot carbon.

CO_2(g)      +     C_(s)     →    2CO_(g)

The reaction is of great importance in the blast furnace and in the manufacture of gaseous fuels.

Test for CO₂: Bubble the unknown gas through a solution of lime water (Calcium hydroxide)if the lime water turns milky due to the formation of insoluble calcium trioxocarbonate (iv), then the unknown gas is CO₂

Ca(OH)_2(aq)        +      CO_2(g)     →   CaCO_3(s)     +       H₂O_(l).

If the gas is bubbled in excess, the milkiness disappears and turns to a clear solution due to the formation of soluble calcium hydrogen trioxocarbonate (iv).

CaCO_3(s)    +   H₂O_(l)    +   CO_2(g)      →     Ca(HCO₃)_(aq)

Finally, if the clear solution is heated, the milkiness reappears due to the decomposition of soluble Ca(HCO₃)₂ to form insoluble CaCO₃

Ca(HCO₃)_2(aq)      →     CaCO_3(s)    +  H₂O_(l)   +   CO_2(g)

Uses of carbon (iv) oxide

1. It is used as fire extinguishers since it does not support combustion.
2. It gives carbonated (aerated) drinks their refreshing taste. Beer, cider and champagne contains CO₂
3. It is used in the manufacture of Na₂CO₃ (washing soda) by the Solvay process.
4. It is used as a leavening agent in the baking of bread. Yeast and baking powder produces CO₂ which make the dough of bread to rise.
5. It is used in the manufacture of fertilizer (such as urea and (NH₄)₂SO₄.
6. Solid CO₂ (i.e dry ice) is used as a refrigerant for perishable goods e.g. ice cream. (It sublimes on warming and provides a lower temperature).
7. Gaseous CO₂ is used to preserve fruits.
8. CO₂ is also used as a coolant in nuclear reactors.

 

EVALUATION

1. Describe the laboratory preparation of dry carbon (iv) oxide.
2. Write a balanced equation to show the following reactions of CO₂:

(a)  Reaction with sodium hydroxide

(b)  Reaction with burning magnesium

 

CARBON (II) OXIDE

LABORATORY PREPARATION

1. Carbon (ii) oxide can be prepared by passing carbon (iv) oxide through red-hot carbon while the Carbon (iv) oxide is itself reduced to Carbon (ii) oxide. The gaseous mixture is passed through concentrated NaOH to remove the excess Carbon (iv) oxide.

CO_2(g)            +       C_(s)    →    2CO_(g)

The pure Carbon (ii) oxide is collected over water.

2. Carbon (ii) oxide can also be prepared by the dehydration of methanoic (formic) acid or ethanedioic (oxalic) acid, using concentrated tetraoxosulphate (vi) acid.

HCOOH_(l).

$\stackrel{\mathrm{Conc}. \mathrm{H}2\mathrm{SO}4}{\to }$

CO_(g)   +   H₂O

Methanoic acid

Note: The gaseous mixture is passed through concentrated NaOH to remove the CO₂.

Caution: The preparation of CO must be done in a fume cupboard as the gas is poisonous.

The major air pollutants that can result from smoky vehicles are Carbon (ii) oxide and Carbon particles.

When CO is breath in for any length of time, even 1% of it in the air may cause death, which makes it clear how dangerous it can be to run a car engine in a closed garage or a generator in a closed room. Very often the victim collapse without warning so insidious is its effect.

PHYSICAL PROPERTIES OF CO

(1) CO is a poisonous, colourless, tasteless and odourless gas.

(2) It is insoluble in water but dissolves in a solution of ammoniacal copper (i) chloride.

(3) It is neither lighter nor heavier than air.

(4) It is neutral to litmus.

CHEMICAL PROPERTIES OF CO

1. As a reducing agent:

CO is a strong reducing agent. It reduces some metallic oxides to the metals and it is oxidized to CO₂.

PbO_(s)   +    CO_(g)      →    Pb_(s)         +       CO_2(g)

Fe₂O_3(s)  +   3CO_(g)    →     2Fe_(s)        +       3CO_2(g)

CuO_(s)    +    CO_(g)     →    Cu_(s)         +       CO_2(g)

2. Combination reaction:

(a). With oxygen: CO burns in air with a faint pale blue flame to form CO₂.

2CO_(g)      +      O_2(g)    →   2CO_2(g)

(b).  With haemoglobin: CO combines irreversibly with haemoglobin in the red blood cells to form carboxy-haemoglobin thereby preventing the red corpuscle from acting as an oxygen carrier.

3. CO mixed with NaOH at 150⁰C under 50atm pressure to form Sodium formate.

CO_(g)       +     NaOH_(aq)     →    HCOONa_(aq)

This product decomposes into Sodium oxalate and H₂ at 400⁰C

2HCOONa_(aq)      +    H_2(g)  ^4000C  →  COONa

4. CO combined with certain metals (e.g Ni, Fe, Cobalt) when hot to form a volatile carbonyl.

Ni_(s)    +     4CO_(g)    →    Ni(CO)_4(aq)

5. CO is absorbed readily by a solution of Copper (i) Chloride (CuCl) in aqueous NH₃ or conc. HCl forming a compound, CuCl.CO.2H₂O. This reaction is used to separate CO from a mixture of gases.

CO_(g)  +  CuCl_(s)   +  2NH₄OH_(aq)     →      CuCl.CO.2H₂O_(aq)    +   2NH_3(g)

6. CO combined with Chlorine gas when exposed to ultra-violet light or passed over a catalyst of activated charcoal at 150⁰C to form carbonyl chloride.

CO_(g)     +       Cl_2(g)    →   COCl_2(g)

This product, COCl₂, is also known as Phosgene and was employed as a poisonous gas in the First World War. It is now used in the manufacture of dyestuff.

Test for Carbon (ii) oxide

When a lighted splint is inserted into a test tube containing CO_(g) and some lime water added to it and shaken, the CO_(g) burn with a pale-blue flame and turn lime water milky after burning but not before burning.

Uses of Carbon (ii) oxide

(1) CO is used in the extraction of metals from their ores.

(2) It is also an important constituent of gaseous fuels like producer gas and water gas.

(3) CO gas is used in the manufacture of methyl alcohol, synthetic petrol, carbonyl chloride, oxalate and formate.

 

EVALUATION

1. Describe the laboratory preparation of Carbon (ii) oxide.
2. Explain why Carbon (ii) oxide cannot be collected by any method of delivery
3. Write two equations to show the chemical properties of carbon (ii) oxide

 

In our next class, we will be talking about Coal and Fuel Gases.  We hope you enjoyed the class.

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