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Heating Things Up

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Author: Janice VanCleave

What Effect Does Salt Concentration Have on the Specific Heat of an Aqueous Salt Solution

Category: Physics—Energy—Heat

Project Idea by: Daniel O'Leary and John Paul Carollo

Question: What Effect Does Salt Concentration Have on the Specific Heat of an Aqueous Salt Solution?

Heat is the energy that is transferred between objects because of differences in their temperature. It moves from an object with a higher temperature to one with a lower temperature. Specific heat is a measure of how well a material resists changing its temperature. A material with a low specific heat changes temperature easily; it has to gain or lose only a small amount of heat to increase or decrease its temperature. The opposite is true for a material with a high specific heat.

Pots and pans should be made with materials having low specific heats. That way, it doesn't take much heat to get the pot or pan hot, and most of the heat goes into cooking the food. Wood has a higher specific heat than metal. When the same amount of heat is added, a wooden handle on a pot does not get as hot as a metal handle.

Water has a very high specific heat: 1 cal/g °C. One calorie of heat is needed to raise the temperature of 1 gram of water 1°C. This specific heat is for pure water. A project question might be, "What effect does salt concentration have on the specific heat of an aqueous salt solution?"

Clues for Your Investigation

Design a safe method of measuring temperature changes. One way is to cool the water and water-and-salt solutions instead of heating. Start with a measured amount of distilled water at room temperature. The water can be cooled by placing the container in the refrigerator or surrounding it with ice. Measure the temperature every 5 minutes for 30 or more minutes. Repeat the experiment using the same amount of water but with different amounts of salt mixed in.

Independent Variable: Amount of salt

Dependent Variable: Temperature change

Controlled Variables: Amount of water, type of containers, method of cooling, time intervals for measuring

Control: Distilled water

Other Questions to Explore

  1. Do other kinds of solutes such as sugar or baking soda affect the specific heat of an aqueous solution?
  2. How can the specific heat of different solids be compared?
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