To Prepare carbon dioxide gas in the laboratory

Experiment 12: TO PREPARE CARBON DIOXIDE GAS IN THE LABORATORY

OBJECTIVE

TO PREPARE CARBON DIOXIDE GAS IN THE LABORATORY AND INVESTIGATE ITS PROPERTIES.

APPARATUS REQUIRED

Woulfe’s bottle
Thistle funnel
Delivery tube
Cork
Gas jars
Test tube

CHEMICALS REQUIRED

Dilute HCl
Marble chips
NaOH
Litmus paper
Mg ribbon
Lime water

THEORY

Carbonates are decomposed by dilute mineral acids with effervescence. Carbon dioxide is prepared in the laboratory by the action of dilute hydrochloric acid on marble chips. This gas is produced according to the following chemical reaction.

Molecular reaction:

CaCO_{3}+2HCl\rightarrow CaCl_{2}+ H_{2}O+CO_{2}

Ionic reaction:

CO_{3}^{--}+2H^{+}\rightarrow Ca^{++}+ H_{2}O+CO_{2}

Dilute sulphuric acid is not used in this preparation. It is due to the formation of soluble calcium sulphate which covers the marble chips and prevents further contact of chips with acid, hence stopping the further formation of gas.

To Prepare carbon dioxide gas in the laboratory

PROCEDURE

Some marble pieces were placed into the Woulfe’s bottle and water was poured over the marble chips. The apparatus was fitted as shown in the figure. Dilute hydrochloric acid was added through the thistle funnel such that the lower end of the funnel dips under the solution. Reaction occurs with effervescence. Since the gas is soluble in water and heavier than air, it was collected by upward displacement of air.

OBSERVATION TABLE

Experiment	Observation	Inference
1. The physical properties was noted i. Colour ii. Odour iii. Solubility: The gas jar filled with hydrogen gas was inverted over a water trough and moved it up and down for some time.	1. i. No color ii. No odour iii. The level of water slightly raised in the jar.	1. The gas is i. colourless ii. Odourless iii. Slightly soluble in in water.
2. A burning candle was introduced into the gas jar full of CO₂ gas.	2. The burning candle gas extinguished.	2. CO₂ gas is neither combustible nor the supporter of combustion.
3. A piece of burning magnesium was introduced into the jar full of CO₂ gas.	3. Magnesium burned forming black particles and white residue.	3. CO₂ gas can support the combustion of brilliantly burning Mg.
4. Moist blue litmus paper was brought into contact with CO₂ gas.	4. Blue litmus paper turned faintly red.	4. CO₂ gas is weakly acidic.
5. A test tube was filled with CO₂ gas. A few drops of NaOH were added to it. Its mouth was closed with thumb, shaked and inverted over a water trough.	5. The level of water rises up high in the tube.	5. The gas is highly absorbed by NaOH solution.
6. The gas was passed into the lime water taken in a test tube.	6. Lime water turned milky white.	6. Formation of white insoluble carbonate.
7. The gas was continued to pass for some more time.	7. The precipitate disappeared and the solution became colourless.	7. Formation of soluble substances.
8. The clear solution obtained in 7 was heated.	8. Turbid precipitate reappeared.	8. A white insoluble substance was formed again.

REACTIONS INVOLVED

1. Action with water

CO_{2}+H_{2}O\rightarrow \underset{weak\ acid}{H_{2}CO_{3}}

3. CO₂ is decomposed by burning Mg.

CO_{2}+2Mg\rightarrow \underset{white}{2MgO}+\underset{black}{C}

5. Action of NaOH

CO_{2}+2NaOH\rightarrow Na_{2}CO_{3}+H_{2}O

6. Action with lime water

Ca(OH)_{2}+CO_{2}\rightarrow CaCO_{3}+ H_{2}O

7. With excess CO₂

CaCO_{3}+CO_{2}+ H_{2}O\rightarrow \underset{\underset{bicarbonate}{colorless\ soluble}}{Ca(HCO_{3})_{2}}

8. Heating of calcium bicarbonate

Ca(HCO_{3})_{2}\rightarrow CaCO_{3}+H_{2}O+CO_{2}

RESULT

Carbon dioxide gas is prepared in the lab and its properties are studied.

CONCLUSION

In this way, carbon dioxide gas is prepared in the laboratory and its properties are studied.

PRECAUTIONS

Apparatus as fitted must be air-tight.
The lower end of the thistle funnel must be under the surface of water.
Dilute sulphuric acid is not used in this preparation instead of dilute hydrochloric acid.

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