To study the properties of an acid (HCL) by its reaction with Litmus solutions, Zinc Metal and Solid Sodium Carbonate

Aim

To study the properties of an acid (HCL) by its reaction with:

1. Litmus solutions (Blue and Red)
2. Zinc metal
3. Solid sodium carbonate

Material and Apparatus Required

Test tubes, test tube stand, a dropper or a glass rod, litmus solutions (blue and red), hydrochloric ac zinc metal, sodium carbonate, soap solution, candle, delivery tube.

Theory

Hydrochloric acid turns blue litmus red while it does not affect red litmus. Hydrochloric acid reacts with zinc metal to produce hydrogen gas.
Zn (s) + 2HCL (aq) -> ZnCl2 (aq) + H2 (g)
[Zinc + Hydrochloric Acid -> Zinc Chloride + Hydrogen]

Hydrogen gas burns with a pop when a burning candle is brought in contact with the gas.
2H2(g) + O2(g) -> 2H2O (/)
[Hydrogen + Oxygen -> Water]

Hydrochloric acid reacts with sodium carbonate to produce carbon dioxide.
Na2CO3 (s) + 2HCL (aq) -> 2NaCl (aq) + H2O (/) + CO2 (g)
[Sodium Carbonate + Hydrochloric Acid -> Sodium Chloride + Water + Carbon Dioxide]

Carbon dioxide gas turns lime water [Ca(OH)2] milky.
Ca(OH)2(aq) + CO2 (g) -> →CaCO3(s) + H2O (/)
[Calcium Hydroxide + Carbon Dioxide -> Calcium Carbonate + Water]

Procedure

1. With Litmus Solution

Experiment 1:

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

Observation

Blue litmus turns red.

Inference

HCl is acidic in nature.

Experiment 2:

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

Observation

Red litmus remains unchanged.

Inference

HCl is acidic in nature.

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

The gas produced is hydrogen.

Experiment 2:

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

Observation

Candle is extinguished and gas burns with a pop sound.

Inference

The gas produced is hydrogen.

3. With Sodium Carbonate

Experiment 1:

Take about 0.6 g of sodium carbonate (Na2CO3) in a test tube. Add about 3 mL of dilute HCl to it.

Observation

CO2 is produced with an effervescence (a rapid evolution of gas).

Inference

Gas produced is CO2.

Experiment 2:

Pass this gas through lime

Observation

Lime water turns milky.

Conclusion

1. Hydrochloric acid (HCL) turns blue litmus red while red litmus remains unaffected.
2. HCl reacts with zinc metal and produces H₂ gas.
3. HCl reacts with sodium carbonate and produces carbon dioxide gas.
4. Hydrochloric acid is acidic in nature.

Precautions

• Use clean zinc granules.
• Cover zinc metal completely in HCL solution.
• Always carry out the test for hydrogen with a very small volume of gas.
• Handle hydrochloric acid carefully because it can burn skin and clothes.
• Shake the solutions without spilling.