Carbon dioxide (Carbon(IV) oxide)

Preparation of carbon dioxide

Carbon dioxide can be prepared by action of a dilute acid on marble chips (calcium carbonate).
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)

Note

Sulphuric acid is not used in the preparation of carbon dioxide because the salt formed (calcium sulphate) forms a coating on the surface of calcium carbonate and this prevents further reaction between the acid and calcium carbonate as calcium sulphate coating is insoluble.

Potassium hydrogencarbonate solution absorbs any traces of hydrochloric acid from the carbon dioxide.

The gas is then dried by passing it through U-tube packed with anhydrous calcium chloride.

Carbon dioxide is collected by downward delivery because it is denser than air.

PROPERTIES OF CARBON DIOXIDE

(a) Physical properties of carbon dioxide

  1. It is a colourless.
  2. It has odourless.
  3. It is denser than air.
  4. It is slightly soluble in water.
  5. Solid carbon dioxide is referred to as dry ice. Dry ice sublimes changing directly to gas.

(b) Chemical properties of carbon dioxide.

  1. Reaction with water
    CO2 + H2O ⇌ H2CO3
  2. Reaction with oxygen.

    It does not support combustion. It supports the combustion only of strongly burning metals like magnesium.

    The reaction is possible because the heat supplied by burning magnesium first decomposes carbon dioxide to carbon and oxygen which then reacts with magnesium to form magnesium oxide.

    2Mg(s) + CO2(g) → 2MgO(s) (white ash)+ C(s)(black)
    A white ash and black specks of carbon are formed.

  3. Carbon dioxide reacts with alkalis to form carbonates and in excess the bicarbonate (hydrogencarbonate) are formed.
    (a) NaOH + CO2 → Na2CO3 + H2O
    Na2CO3 + H2O + CO2(in excess) → NaHCO3.

    (b) Ca(OH)2 + CO2 → CaCO3 + H2O
    In excess of CO2 the following reaction occurs:
    CaCO3 + H2O + CO2 → Ca(HCO3)2

    4. Test for carbon dioxide

    Carbon dioxide turns lime water milky.
    Ca(OH)2 (aq)(lime water)+ CO2(g) → CaCO3(s)(milky) + H2O(l)

    Uses of carbon dioxide

    1. It is used in fire extinguisher because it does not support combustion.
    2. It used in the manufacture of aerated drinks because the solution of the gas in water has a pleasant taste.
    3. It used as in refrigerators as dry ice (carbon dioxide ) because dry ice sublimes slowly leaving no residue.
    4. Carbon dioxide is used by plants during photosynthesis.
    5. It is used in making baking powder.
    6. It is used to rain.
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