Chemical Reaction Experiments

Activity 1

Take a little mercury in a hard glass test tube. It has a silvery shining colour. Heat the test tube slowly. You will notice that mercury changes into reddish powder. It is because of the combination of mercury with oxygen from air. Mercury and oxygen together form oxide of mercury.

2Hg + O₂ = 2HgO

Mercury + Oxygen ----> Mercury oxide

Activity 2

Take about 5 ml, of hydrogen peroxide (H₂O₂) in a test tube (15 mL). Add to it a little amount of manganese dioxide. You will notice that the bubbles start coming out from the mixture. Take a burning incense stick near the mouth of the test tube. The stick glows indicating the presence of oxygen. In the presence of manganese dioxide, hydrogen peroxide decomposes into water and oxygen as shown in the following equation. .

2H₂O₂ --------------> 2H₂0 + 0₂

hydrogen peroxide --------------> water + oxygen

Activity 3

Take a few zinc granules in a test tube (15ml) and add to it about 5 mL of dilute hydrochloric acid. : Bubbles of a gas will start coming s out. Take a burning candle near the mouth. You will hear a pop sound indicating the presence of hydrogen. In this reaction, zinc replaces hydrogen from the hydrogen chloride (HC1). The replaced hydrogen gets released in the form of a gas and zinc chloride (ZnCl2) formed in the reaction gets dissolved in water.

Zn + 2 HCl-------> ZnC1₂ + H₂

Activity 4

Take 25 mL of dilute solution of sodium hydroxide in a conical flask (250 mL) and add to it a drop of phenolphthalein indicator. The solution will acquire pinkish color. Fill the burette with dilute hydrochloric acid and pour it drop by drop into the flask. As the two solutions get mixed, the pink color gets fainter and fainter. Soon, the pink color disappears. Test this mixture using red and -blue litmus papers. You will notice that both red and blue litmus retain their colors. It means solution is now neutral.

Activity 5

Take a piece of coal and prepare a small pit into it. Put a little red lead into the pit and blow

Fig Reduction of red lead

the flame towards the powder as shown in Fig. You will notice that the colour of the powder changes from red to yellow. As you continue to blow the flame, you will find a greyish liquid in the pit, which on cooling becomes solid. It is lead. The reaction can be : shown by the following equation.

Pb₃O₄ + 2C ~ 3Pb + 2C0₂