State a simple experiment to observe melting and boiling points.

State a simple experiment to observe melting and boiling points.

• A. Use a thermometer to measure the temperature as ice melts at 0°C and water boils at 100°C, recording the temperatures during the changes.
• B. Use a thermometer to measure the color change as a substance is heated.
• C. Heat ice to observe melting at 0°C, then heat water to observe boiling at 100°C, recording temperatures during changes.
• D. Heat a substance until it forms crystals and note the temperature.

Answer: (C)

Melting and boiling points are the temperatures at which a pure substance changes phase at a given pressure, so a simple way to see them is to watch a sample as you heat it and measure temperature continuously. Start with ice and use a thermometer. As you add heat, the ice will melt at about 0°C, and the temperature will stay around 0°C while the solid becomes liquid. Once everything is melted, the temperature will rise again until it reaches about 100°C, at which point the liquid starts to boil and the temperature stays near 100°C as it changes to steam. Recording the temperatures during these changes gives you clear observed values for both the melting point and the boiling point. This is why the described experiment—heating ice to observe melting at 0°C, then heating the water to observe boiling at 100°C, with temperatures recorded during the changes—is the best simple demonstration.

Melting and boiling points are the temperatures at which a pure substance changes phase at a given pressure, so a simple way to see them is to watch a sample as you heat it and measure temperature continuously.

Start with ice and use a thermometer. As you add heat, the ice will melt at about 0°C, and the temperature will stay around 0°C while the solid becomes liquid. Once everything is melted, the temperature will rise again until it reaches about 100°C, at which point the liquid starts to boil and the temperature stays near 100°C as it changes to steam. Recording the temperatures during these changes gives you clear observed values for both the melting point and the boiling point.

This is why the described experiment—heating ice to observe melting at 0°C, then heating the water to observe boiling at 100°C, with temperatures recorded during the changes—is the best simple demonstration.