(2014?Quzhou) Xiaoli uses a large test tube with a small hole at the bottom to formulate a device to produce CO2 gas as shown in Figure A. (1) Before the experiment.

(1) the principle of checking the tightness of the device are based on the pressure difference between the inside and outside of the device to form a column of water or bubbles; therefore, the device to check the tightness of the method is: close the stopcock (or block the catheter with your finger), the bottom part of the test tube through the bottom immersed in water, and then hold the test tube in your hand and observe whether there are bubbles coming out of the bottom of the bottom of the through the test tube. Observed bubbles at the bottom of the test tube, the device is well sealed;

(2) in the collection of CO2 in a soft plastic bottle (as shown in Figure B), add the appropriate amount of NaOH solution, cover the stopper and shake, the bottle deflated, so that the CO2 reacted with the NaOH, Qu questioned the cause of the deflated soft plastic bottles may also be the cause of carbon dioxide soluble in water;

(3) in the soft plastic bottle (as shown in Figure B), the bottle deflated, so that the CO2 reacted with NaOH, Qu questioned the cause of the deflated soft plastic bottles may also be the cause of carbon dioxide dissolved in water;

(3) The reaction between CO2 and NaOH has the production of sodium carbonate, so if you add calcium chloride solution will have a white precipitate, it proves that the reaction between CO2 and NaOH has indeed occurred.

The answers are:

(1) bubbles coming out of the bottom of the test tube;

(2) carbon dioxide dissolves in water;

(3) calcium chloride.