Mixers: Can the Addition of Sugar to Water form a Homogeneous Mixture?

Problem

Can the addition of sugar to water form a homogeneous mixture?

Materials

• spoon
• drinking glass
• dishwashing liquid
• tap water
• paper towel
• distilled water
• 1 teaspoon (5 ml) sugar
• clean drinking straw

Procedure

CAUTION: Never taste anything in a laboratory setting unless you are sure that there are no harmful chemicals or materials and that all containers are properly cleaned. This experiment is safe, since only sugar and water are present.

1. Prepare the materials by washing the spoon and glass in soapy water.
2. Rinse the spoon and glass in clear water, and dry them with the paper towel.
3. Fill the cleaned glass half full with distilled water.
4. Add the sugar to the distilled water.
5. Stir until no sugar particles can be seen.
6. Stand the straw in the glass containing the sugar-water mixture.



7. Collect a sample of the sugar-water mixture by keeping your finger over the top of the straw as you draw the straw out of the glass.
8. Taste the sample and make a mental note of its sweetness.
9. Use the straw to taste samples from the bottom, middle, and top of the sugar-water mixture.
10. Compare the taste of the three samples.

Results

All three samples have the same sweet taste.

Why?

In this experiment, sugar is a solute, a substance that breaks into smaller parts when dissolved in another substance called a solvent—in this case, water. The dissolved particles of a solute move freely throughout the solvent. The combination of a solute with a solvent is called a solution. The molecules in the crystals of sugar separate and move between the molecules of water. The sugar-water solution is homogeneous, meaning the ratio of sugar molecules to water molecules in the solution is the same throughout. Samples of equal volume taken from the solution contain the same ratio of sugar molecules to water molecules regardless of where the samples were taken.

Let's Explore

1. How much sugar will dissolve in water? Use 1 cup (250 ml) of distilled water. Add 1 teaspoon (5 ml) of sugar at a time, stirring after each addition until all the sugar dissolves. Continue to add and record measured amounts of sugar to the water until the particles stop dissolving no matter how much you stir. A solution that will not dissolve any more solute is said to be a saturated solution.
2. Would the amount of sugar needed to make a saturated solution change if the water were not distilled? Repeat the original experiment, using tap water.



3. Does the temperature of the water affect the amount of sugar that will dissolve? Repeat the original experiment three times, using ice water, cold tap water, and warm tap water. Place a thermometer in the water and record the temperature. Remove the thermometer before adding the sugar. Science Fair Hint: You can use a data chart like the one shown to record and display the temperature of each liquid and the amount of sugar needed to produce a saturated solution.

Show Time!

1. Make a diagram such as the one shown to explain the following terms: solute, solvent, solution, dilute, concentrated, saturated, and unsaturated.
2. Solutions are mixtures in which a substance is dissolved in another substance. The sugar-water solution is an example of a solid dissolved in a liquid. Learn about and display other types of solutions such as:
   • a gas dissolved in a liquid (soda)
   • a gas dissolved in a gas (air)
   • a liquid dissolved in a gas (water in air)

Saturated Solutions

Temperature versus Amount of Solute

Check it Out!

A solid dissolved in a solid is called an alloy. When metals are mixed together, their properties change. Brass is an alloy of zinc and copper. It is harder and lasts longer than either zinc or copper alone. Alloys are used instead of pure metal because of their special properties. Find out more about alloys such as brass, bronze, pewter, and alnico. What are their special properties, and how are they used?

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Janice VanCleave's Guide to the Best Science Fair Projects
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