Carbon Dioxide Gas

Carbon dioxide is about one and a half times heavier than air, so it can be collected by downward displacement. Fit up a flat-bottomed flask with  a thistle funnel and delivery tube, and set up your apparatus as shown in fig. 31.

flat-bottomed-flask

Weigh out about 25 to 30 grams of marble, broken into small pieces, and transfer carefully to the flask; then pour a little water into the flask, and fit in the thistle funnel and delivery tube. Pour down the thistle funnel some strong hydrochloric acid ; a brisk effervescence follows, and the gas is evolved.

CaCO3 + 2HCl = CaCl2 + H2O + CO2

Collect three jars of the gas. To test when the jars are full, apply a lighted taper to the mouth of each jar; if it is extinguished, you will know the jar is full.

Laboratory Experiment I

Pour a little clear lime-water into a small beaker, dip the end of the delivery tube into this liquid, and allow the carbon dioxide to bubble through it; the clear solution becomes turbid. Continue to pass the gas, and the turbidity disappears after a time. Remove the beaker and boil the clear solution ; the turbidity soon appears again.

equation-2

Laboratory Experiment II

Pour a little blue litmus solution into a small beaker and pass the carbon dioxide gas through it; the solution turns a wine-red colour, differing from the red produced by the action of hydrochloric acid on litmus solution. Boil the wine-red liquid and it becomes blue again.

Laboratory Experiment III

Take a jar of the gas, remove the glass cover, and pour the gas on to a lighted taper; the taper soon goes out.

Laboratory Experiment IV

Pour a little water into another jar of the gas, close the mouth of it with the hand and shake well; invert the jar and place its mouth under water in a trough; remove the hand and the water will rise in the jar showing the solubility of the gas.

Laboratory Experiment V

Take the remaining jar of the gas and pour a little sodium or potassium hydrate solution into it; close its mouth with the hand and shake well, then invert it and bring its mouth under water and remove the hand; the water will rush into the jar, showing that the gas has been absorbed by the solution of sodium or potassium hydrate.

2KOH + CO2 = K2CO3 + H2O

Filter the liquid remaining in the flask, transfer to a porcelain dish and evaporate to dryness, stirring it from time to time to prevent the calcium chloride from sticking to the dish.