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Lesson 3-3: The Water Molecule and Dissolving

Page history last edited by mariaelizabethbunn@... 5 years, 7 months ago

Lesson 

Time

Engaging the Student (Entry Task) 

Developing the Ideas--Lesson

Checking for Understanding (exit ticket)

Student Handout 
Teacher/Lesson Notes
Materials

1 class period 

 Distribute M&M’s to students and have them look at the outside candy coating. Then have students break an M&M to look closely at the coating from the inside.

Ask students:

  1. What do you think the coating of an M&M is made from? Students will see the layer of color with a layer of white beneath it and suggest that the coating is made of sugar and coloring. Explain that the coating is mostly sugar.
  2. Have you ever noticed what happens to the coating of an M&M when it gets wet? The color comes off and if it gets wet enough, the entire coating comes off, leaving the chocolate behind.

Tell students that in this activity, they will see what happens to the sugar and color coating of an M&M when it is placed in water.


 

Optional:

View the full lesson plan here:

 

View answer key to the student activity sheet here:

 

Summary:

  • Students will observe the dissolving of the sugar coating from an M&M when it is placed in water. Students will then help design an experiment to see if the type of liquid the M&M is placed in affects how much of the coating dissolves.

Objectives:

  • Students will be able to explain, on the molecular level, how the polar characteristic of water and sugar interact so that water dissolves sugar.
  • Students will be able to identify and control the variables in their experiment.
  • Students will also be able to explain why a non-polar liquid, such as mineral oil, is not good at dissolving sugar.

 

  • M&M’s
  • Water
  • Mineral oil
  • Isopropyl alcohol (70%)
  • Small white plastic plate
  • 3 clear plastic cups
  • White paper

 

Links for images used in the Discussion part of lesson:

 

 

 

 


Project the following image of Citric Acid:

 

 

Explain that the projected image is a model of a citric acid molecule. Tell students that citric

acid is the substance that gives lemons, limes, grapefruit, and oranges their tangy sour

taste. Citric acid is very soluble in water and is dissolved in the water in the fruit.

 

On Exit Slip, Ask the students:

 

Why do you think citric acid is so soluble in water?

 

HINT: The chemical formula for citric acid is C6H8O7.

Every place there is an O–H bond, there is an uneven sharing of electrons. The oxygen

atoms in an O–H bond have a slightly negative charge and the hydrogen atoms

in the bond have a slightly positive charge. Because water molecules are also polar,

the positive ends of water molecules are attracted to the negative areas of the citric

acid molecules. The negative ends of water molecules are attracted to the positive

areas of the citric acid molecules. These mutual attractions will overcome the attractions

citric acid molecules have for other citric acid molecules, causing them to mix

thoroughly in the water and dissolve.

 

 

 

 

 

 

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