How Salt Affects Freezing of Water

This demonstration compares how quickly plain water and saltwater freeze. By observing two bowls placed in a freezer, students discover that adding salt lowers the freezing point of water, making saltwater take longer to freeze.

1. Label two bowls “Bowl 1” and “Bowl 2.”
2. Pour water into each bowl.
3. Add salt to Bowl 2, stirring until the salt is mostly dissolved.
4. Place both bowls in the freezer at the same time.
5. After one hour, check both bowls to observe any differences in freezing.
6. Optional: use a thermometer to measure and record the temperature of each bowl.
7. Leave the bowls for 24 hours and observe again to see which one froze completely.
8. Discuss how the presence of salt affected the freezing rate and amount of ice formed.

Saltwater Experiment - Susan Evans:

Freezing Point of Water Experiment | Chemistry - The Good and the Beautiful Homeschool Science:

📄 Freezing Water Experiment - Jane Bahrehbar: https://littlebinsforlittlehands.com/freezing-water/

• Try adding different amounts of salt to see how concentration affects freezing rate.
• Test other substances such as sugar, baking soda, or vinegar to compare effects on freezing.
• Measure and record temperature changes over time using a digital thermometer or data logger.

• Handle glass or ceramic bowls carefully to prevent breakage when frozen.
• Do not taste or consume the saltwater samples.
• Wipe up any spilled water promptly to avoid slipping.
• Ensure bowls are placed securely in the freezer to prevent tipping or leaking.

• Which bowl froze faster - plain water or saltwater? (Plain water.)
• Why did the saltwater take longer to freeze? (Salt lowers the freezing point of water.)
• What does this tell us about how salt affects molecular bonding during freezing? (Salt interferes with the ability of water molecules to form ice crystals.)
• How is this concept used in real life, such as when salt is spread on icy roads? (Salt lowers the freezing point of water, helping melt ice and prevent refreezing.)
• Is this a physical or chemical change? (Physical change, because no new substances are formed.)