Lesson 5.4: Why Does Water Dissolve Sugar?

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Sucrose 1

• The ball-and-stick and first space-filling model show that sucrose is a large molecule made up of carbon, oxygen, and hydrogen.
• Sucrose has many O–H bonds which are polar.
• These polar areas are shown with a + near the hydrogen atom and a − near the oxygen atom.
• The second space-filling model shows two sucrose molecules held together by their opposite polar areas.
• These molecules will separate from each other when sucrose dissolves.

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Water Dissolves Sucrose 1

• Water molecules arrange themselves around the sucrose molecules according to opposite polar areas.
• The attraction of the water molecules and their motion overcome the attraction between sucrose molecules.
• The sucrose molecules dissolve as they are separated from the other molecules and mix into the water.

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Sucrose

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• The sucrose molecule has many oxygen-hydrogen (O–H) bonds which are polar.
• The charge-density model shows the positive areas near the hydrogen atom as blue and the negative area near the oxygen atom as red.
• The sugar molecules are attracted and held together in a crystal by these opposite polar areas.

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Water Dissolves Sucrose 2

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• Water molecules arrange themselves around the sucrose molecules according to opposite polar areas.
• The attraction of the water molecules and their motion overcome the attraction between sucrose molecules.
• The sucrose molecules dissolve as they are separated from each other and mix into the water.

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Water, Alcohol, and Oil

• The water is polar, so it dissolves the polar color and sugar.
• The alcohol has a polar area but a larger non-polar area. It is not a good dissolver of color or sugar.
• The oil is non-polar and does not dissolve the color or sugar.

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Citric Acid

• This is a ball-and-stick model of citric acid.
• Citric acid is dissolved in water in oranges, lemons, grapefruit, and other citrus fruits.
• Citric acid dissolves very well in water.