Learning Library

# Effect of Temperature and Salinity on Surface Tension of Water

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### Materials:

• 2 clear glass 250 ml beakers (other types of transparent glassware can also be
• used)
• 1 gallon of distilled water
• Aluminum foil cut into small squares measuring approximately 1 cm x 1 cm
• White rice (size of grain does not matter)
• Table salt
• Thermometer
• Graph paper
• Scissors
• Ruler
• Measuring spoon
• Tweezers

### Procedure:

1. Label one beaker “NaCl” (NaCl stands for sodium chloride - otherwise known as salt). Label the other beaker “pure water.”
2. Fill both beakers with 250 ml of distilled water.
3. Add 3 tablespoons of table salt to the beaker labeled “NaCl.” Stir until the salt is dissolved.
4. Put both beakers in the fridge. After a half hour check the temperature of the liquids. Keep them refrigerated until the temperature of the water drops to 15° C.
5. Float a piece of aluminum foil on the surface of the water. See if you can place individual grains of rice on top of the foil. You may want to use a tweezers to grasp the rice grains. How many rice grains can be placed on the foil in the pure water beaker before they sink? How many grains can be placed on the foil in the saltwater beaker before they sink? Write down your results.
6. Let the beakers sit on a counter until the water is room temperature. Repeat step5.
7. Using a hot plate, heat the water until it is 35°C. If you do not have a hotplate, use a microwave, heating the water for 5-second intervals and checking the temperature after every 5 seconds. Repeat step 5. Try this again when the water is 40°C, 45°C, 50°C, and 55°C.
8. Graph your results. The y-axis of your graph can represent temperature and the x- axis can represent number of rice grains. Surface tension is less if fewer grains of rice are needed to upset the aluminum. Which has less surface tension – saline or pure water? How does temperature affect surface tension?
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