Chemistry

A.  To prevent leaking of hydrogen being prepared and to prevent any air entry in the   test tubes generating hydrogen, because H2 is highly flammable gas.
B. Zinc reacts with dilute Hydrochloric acid to form Zinc Chloride (Clow, 1952).
C.  In the experiment to generate oxygen, manganese is used as a catalyst to speed up the reaction under lower temperature.  Manganese does not change after the reaction. The most common compound of manganese used as a catalyst in oxygen generation experiments is MnO2. However, when pieces of Manganese are used in the reaction to generate Oxygen react with oxygen to form MnO2 (Kiefer, 2002).
D. 2H2  O2  2H2O.
E. Bromthymol blue is an indicator and therefore as a confirmatory test to for presence of carbon dioxide in the experiment,  where it changes to green and then yellow in the presence of CO2.
F. The solution may be assumed to be neutral when Bromothymol blue is a murky green

GasColorGlowing splintLimewater reactionBromthymol blue reactOxygenColorlessIn the presence of oxygen, the glowing splint is re-ignited or re-lighted.No observable changeIt turns from blue to yellow in colorHydrogenColorlessPop sound is produced when glowing splint is put in a container   containing hydrogen.No observable changeThe color of bromothymol blue turns from blue to yellow in the presence of hydrogen, this because the pH of hydrogen is on neutral scale.Carbon dioxideColorlessWhen put a glowing splint in a substance containing carbon dioxide it goes out.The clear lime water will turns into milky precipitate in the presence of carbon dioxide.Turns from blue  to green then yellow in the presence of  carbon dioxide

Oxygen, hydrogen, and carbon dioxide are colorless. Hydrogen burns a glowing splint by producing pop sound. Oxygen re-ignites the glowing, whereas carbon dioxide puts off the glowing splint since it does not support combustion. Hydrogen and oxygen show no observable change when mixed with lime water. However, carbon dioxide reacts with lime water (calcium bicarbonate) making lime water to turn from clear appearance to cloudy or milky precipitate. Therefore, lime water can be used to detect the presence of CO2 gas. Finally, bromothymol blue indicator turns from blue to yellow in color in the presence of oxygen and hydrogen. The indicator turns from blue to green and then yellow in the presence of CO2.