To study the properties of a base (NaOH) by its reaction with Litmus solutions, Zinc Metal and Hydrochloric Acid

Aim

To study the properties of a base (NaOH) by its reaction with:

1. Litmus solutions (Blue and Red)
2. Zinc metal
3. Hydrochloric Acid

Material and Apparatus Required

Test tubes, test tube stand, a dropper or a glass rod, litmus solutions (blue and red), dilute NaOH soultion, phenolphthalein solution, dilute HCL solution and zinc metal

Theory

Sodium Hydroxide turns red litmus blue while blue litmus remains unchanged.

Zinc metal reacts with sodium hydroxide solution to form sodium zincate and hydrogen gas.
Zn (s) + 2NaOH (aq) -> Na2ZnO2 (aq) + H2 (g)
[Zinc + Sodium Hydroxide -> Sodium Zincate + Hydrogen]

Sodium Hydroxide is a base. It neutralises hydrochloric acid solution to produce sodium chloride (common salt) and water.
HCL (aq) + NaOH (aq) -> NaCl (aq) + H2O (/)
[Hydrochloric Acid + Sodium Hydroxide -> Sodium Chloride + Water]

Procedure

1. With Litmus Solution

Experiment 1:

Take 2 mL of red litmus solution in a test tube and add a few drops of dilute sodium chloride to it. Shake the solutions.

Observation

Red litmus turns blue.

Inference

NaOH is basic in nature.

Experiment 2:

Take 2 mL of blue litmus solution in a test tube and add few drops of NaOH to it. Shake the solutions.

Observation

Colour of blue litmus remains unchanged.

Inference

NaOH does not affect blue litmus, therefore it is a base.

2. With Zinc Metal

Experiment 1:

Take about 5 mL of dilute HCl in a test tube. Add a few pieces of zinc granules to it as shown in Figure.

Observation

Some gas bubbles are formed on the surface of zinc granules.

Inference

Zinc reacts with NaOH and produces gas.

Experiment 2:

Pass the evolved gas through the soap solution. Bring a burning candle near a gas filled soap bubble.

Observation

Gas burns with a pop sound.

Inference

Gas produced is hydrogen.

3. With Hydrochloric Acid

Experiment 1:

Take about 2mL of dilute NaOH solution in a test tube. Add about 2 drops of phenolphthalein solution to it.

Observation

The colour of solution is pink.

Inference

NaOH is alkali.

Experiment 2:

Add dilute HCL solution drop-by-drop to the above solution.

Observation

Pink colour disappear.

Inference

The effect of base (NaOH) is nullified by an (HCL) and vice-versa.

Experiment 3:

Add a few drops of NaOH to the above solution.

Observation

The pink colour of phenolphthalein reappears.

Inference

The effect of base (NaOH) is nullified by an (HCL) and vice-versa.

Conclusion

1. Dilute sodium chloride turns red litmus blue but it does not affect blue litmus. Its shows that sodium hydroxide is a base.
2. Sodium chloride reacts with zinc metal and produces hydrogen gas along with the formation of sodium zincate.
3. The effect of NaOH (a base) is nullified by HCL (an acid) and vide-versa.

Precautions

• Use clean zinc granules.
• Cover zinc metal completely in NaOH solution.
• Handle sodium chloride solution carefully.