**Experiment Setup to Demonstrate Sublimation of Ammonium Chloride**

**Materials Required:**

1. Ammonium chloride (NH4Cl)
2. Heat-resistant container (such as a test tube or beaker)
3. Bunsen burner or heat source
4. Wire gauze or tripod stand
5. Heat-resistant mat
6. Thermometer
7. Glass rod or stirring rod
8. Safety goggles and gloves
9. Stopwatch or timer

**Procedure:**

1. **Preparation of Ammonium Chloride:**
- Measure an appropriate amount of ammonium chloride (NH4Cl) using a balance.
- Ensure that the sample is pure and free from any impurities.

2. **Setting up the Experiment:**
- Place the heat-resistant container (such as a test tube or beaker) on a heat-resistant mat.
- Secure the container using a wire gauze or tripod stand to prevent it from tipping over during heating.
- Attach the Bunsen burner or heat source to a gas supply and position it under the container.
- Ensure that there is proper ventilation in the area to prevent the build-up of potentially harmful gases.

3. **Adding Ammonium Chloride:**
- Carefully transfer the measured ammonium chloride into the heat-resistant container.
- Use a glass rod or stirring rod to spread the ammonium chloride evenly across the bottom of the container.

4. **Heating and Observing:**
- Turn on the Bunsen burner or heat source and adjust the flame to a medium heat setting.
- Observe the ammonium chloride as it starts to heat up.
- Monitor the temperature using a thermometer and record the initial temperature.
- Continuously observe the container for any physical changes, such as the formation of gas or the disappearance of solid crystals.
- Note the time it takes for the solid ammonium chloride to sublimate completely.

5. **Recording Data:**
- Record the final temperature once the sublimation process is complete.
- Calculate the temperature change by subtracting the initial temperature from the final temperature.
- Note down the time taken for complete sublimation.

6. **Safety Precautions:**
- Wear safety goggles and gloves to protect your eyes and hands from potential harm.
- Handle the heat source with caution to prevent burns.
- Ensure proper ventilation to avoid inhaling any potentially harmful gases.

**Explanation:**

The experiment demonstrates the sublimation process, where a solid substance, in this case, ammonium chloride (NH4Cl), directly converts into a gaseous state without passing through the liquid phase. The setup involves heating the ammonium chloride to a temperature higher than its sublimation point.

By heating the ammonium chloride in a heat-resistant container, the solid crystals gradually turn into gas, which is visible through the disappearance of the solid substance. The time taken for complete sublimation and the temperature change during the process provide valuable data about the sublimation characteristics of ammonium chloride.

Overall, this experiment helps to illustrate the sublimation process and provides a practical demonstration of the physical change that occurs when a solid substance directly converts into a gas.

Given in ncert book read carefully in ch 1