28 



From these results state your conclusion concerning the 

 effect of oxygen on combustion. 



EXPERIMENT 17. TO MAKE CARBON DIOXIDE 



Put broken bits of marble into a test tube and pour over 

 them hydrochloric acid. Collect the bubbles of gas which 

 are formed, in a second test tube, as shown in Figure 21. 

 What is the color of the gas ? Has it an odor ? Thrust a 



FlG. 21. Making carbon dioxide. 



burning splinter into the test tube containing the gas. 

 Does the gas support combustion ? 



Mention several ways in which carbon dioxide (CO 2 ) and 

 oxygen (O) differ. 



EXPERIMENT 18. TESTING FOR CARBON DIOXIDE 



Carbon dioxide turns limewater milky. 



(a) Put a small quantity of limewater in an evaporating 

 dish and let it remain uncovered on your desk during the 

 laboratory period. Does any change occur in it ? If so, 

 explain why. 



