Carbon IV oxide at a glance

 CARBON (IV) OXIDE: - About 0.03% of atmospheric air is Carbon (IV) oxide by volume while dissolved air contains about 0.50% by volume. This percentages are usually maintained by processes which use up and releases CO2 into the atmosphere, such processes include burning of fossil fuels and organic materials, respiration, deforestation and Photosynthesis 

 

Laboratory preparation

Carbon (IV) oxide is prepared in the laboratory by the action of dilute hydrochloric acid on CaCO₃ which can be in the form of   marble chips or limestone. 

Reaction between CaCO₃ and HCl can be carried out in a Kipp’s apparatus.

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

Note: The dry gas is obtained by passing the gas through potassium hydrogen trioxocarbonate (IV) solution to remove any acid fumes and then through fused Calcium chloride in a U-tube to dry the gas. The dry gas is then collected by downward delivery because it is heavier than air.

INDUSTRIAL PREPARATION

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

 

PHYSICAL PROPERTIES

(1) CO₂ is a colourless.

(2) It is an odourless gas with a sharp refreshing taste.

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

(4) It is soluble in water.

(5). CO₂ dissolves in water to yield trioxocarbonate (IV) acid.

(6) It readily liquefies and solidifies at -78⁰C on cooling to form a white solid known as dry ice.

 

CHEMICAL PROPERTIES

1). It turns damp blue litmus paper pink because

1. Reaction with water: Carbon (IV) oxide dissolves in water to form trioxocarbonate (IV) acid (Soda water). It is a weak dibasic acid ( i.e it ionizes slightly)

(a)  CO_2(g) + H₂O_(l)→H₂CO_3(aq)

On heating rioxocarbonate (IV) acid it decomposes to form H₂O_(l) and CO_2(g).

 

2. Reaction with alkalis: It reacts to form  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:  when passed over burning Na, K andd Mg CO₂ is reduced to carbon.

      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 when passed over red-hot coke.

          CO_2(g) + C_(s) →2CO_(g)

The reaction is important 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 CO_2(g) is bubbled in excess, the milkiness will disappear and turn to a clear solution. This is 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 is used in making carbonated (aerated) drinks their refreshing taste.

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.

Objective Questions 

1. Kipp’s apparatus is important in the laboratory because it 

(a) allows intermittent supply of gases. 

(b) is used for preparing poisonous gases.

 (c) is used to prepare light gas

. (d) is used to prepare sensitive gas

2.  Where else is CO₂ found in free state apart from the atmosphere?

(a) In carbonated drinks.

 (b) Dissolved form in water. 

(c) In corals. 

(d) In limestone region

Theory Questions 

1) State the property of CO₂ that makes it to be used in

 (i) carbonated drinks (ii) fire extinguishers

(b). State what is observed when 

(i) excess CO₂ is bubbled through lime water. (ii) the solution in b(i) above is heated.