EXERCISE VI. 

 CARBON DIOXIDE— A COMPOUND MUCH USED BY PLANTS. 



Supplies for a Laboratory Section of Twelve. A half pound of marble dust; twelve reagent bottles rilled with 

 hydrochloric acid; limewater; twelve elbow tubes; twelve one-hole rubber stoppers; twenty-tour test tubes. 



1. Place some small pieces of marble in a test tube and pour a little hydrochloric acid 

 over them, (a) Observe what happens in the tube. The cause of this action is that the acid 

 acts on the marble, setting carbon dioxide free, (b) Observe the color of the gas. 



2. Lower a burning match into the gas. Observe any effect upon the flame. 



3. Try to light the gas as it is given off. (a) Observe whether or not it will burn, 

 (b) Which of the two gases previously studied does it most resemble? (c) Why? 



4. Place a cork fitted with an elbow tube in the test tube and let the free end of the 

 elbow tube dip into another test tube about haTf filled with limewater. Allow the gas to bub- 

 ble through the limewater for a short time, (a) Observe any change in the appearance of 

 the limewater. This is the only gas present in the atmosphere which affects the limewater 

 this way. 



5. (a) Why is the limewater test necessary in order to distinguish carbon dioxide from 

 nitrogen? (b) How may you distinguish between carbon dioxide and oxygen? (c) Of the 

 three gases studied, which is the most inactive? 



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