Test Hydrochloric acid with Phenolphthalein in ACIDS AND BASES – Class 7 Science Experiment

Chapter Name: ACIDS AND BASES

Activity Name: Test Hydrochloric acid with Phenolphthalein in ACIDS AND BASES

Activity Description:

Test Hydrochloric acid with Phenolphthalein in ACIDS AND BASES - Class 7 Science Experiment

This experiment aims to observe the reaction between hydrochloric acid and phenolphthalein indicator, and then neutralize the acidic solution using a caustic soda solution (sodium hydroxide) until it becomes neutral.

Finally, the neutralized solution will be re-acidified by adding hydrochloric acid drop by drop until it returns to its original acidic state.

Required Items:

  1. Clean test tube
  2. Hydrochloric acid
  3. Phenolphthalein indicator solution
  4. Caustic soda solution (sodium hydroxide)
  5. Dropper

Step by Step Procedure:

  1. Take a clean test tube.
  2. Using a clean dropper, carefully add 10 drops of hydrochloric acid to the test tube.
  3. Add 2 drops of phenolphthalein indicator solution to the test tube.
  4. Observe and note the color of the resulting solution.

Experiment Observations:

  1. Initially, the solution in the test tube will have a certain color due to the presence of hydrochloric acid and phenolphthalein indicator.
  2. Start adding caustic soda solution drop by drop to the test tube.
  3. After each drop, shake the test tube well and observe if there is any change in the color of the solution.
  4. Continue adding caustic soda solution drop by drop until the color of the solution turns pink. The pink color indicates that the hydrochloric acid has been neutralized, and a basic solution is formed.
  5. Now, add one drop of hydrochloric acid to the pink solution and observe if it changes back to its original (colorless) state.
  6. If the solution does not become colorless after adding one drop of hydrochloric acid, add one more drop, and keep doing this until the solution in the test tube becomes colorless again.

Precautions:

  1. Handle hydrochloric acid and caustic soda (sodium hydroxide) with care, as they are corrosive chemicals. Wear appropriate safety equipment such as gloves and goggles.
  2. Perform the experiment in a well-ventilated area to avoid inhaling any fumes.
  3. Use clean and dry equipment to ensure accurate observations.

Lesson Learnt from Experiment:

This experiment demonstrates the concept of neutralization, which occurs when an acid and a base react to form a salt and water. Initially, the hydrochloric acid is acidic and reacts with the phenolphthalein indicator, resulting in a certain color.

As caustic soda (a base) is added to the solution, it neutralizes the acid, turning the solution pink. By adding hydrochloric acid drop by drop, the solution returns to its original colorless acidic state, showcasing the reversible nature of acid-base reactions.

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