Topics addressed

1. Density of solids, Density of liquids, Conservation of Matter, Investigation/Explanation
2. Center of Mass, States of Matter

 

Standards:

Event A.             Density and Buoyancy

8. All objects experience a buoyant force when immersed in a fluid. As a basis for understanding this concept:
1. Students know density is mass per unit volume.
2. Students know how to calculate the density of substances (regular and irregular solids and liquids) from measurements of mass and volume.
3. Students know the buoyant force on an object in a fluid is an upward force equal to the weight of the fluid the object has displaced.
4. Students know how to predict whether an object will float or sink.

Event B. Reactions
Chemical reactions are processes in which atoms are rearranged into different combinations of molecules. As a basis for understanding this concept:
5.d. Students know physical processes include freezing and boiling, in which a material changes form with no chemical reaction.

Structure of Matter

3. Each of the more than 100 elements of matter has distinct properties and a distinct atomic structure. All forms of matter are composed of one or more of the elements. As a basis for understanding this concept:

d. Students know the states of matter (solid, liquid, gas) depend on molecular motion.

5. Students know that in solids the atoms are closely locked in position and can only vibrate; in liquids the atoms and molecules are more loosely connected and can collide with and move past one another; and in gases the atoms and molecules are free to move independently, colliding frequently.

Events A & B

Investigation and Experimentation

9. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations.

 

Description of Investigation

1. Floating-

How?

• Two raw eggs are placed on the lab bench. 
• Two beakers of water are on the lab bench.  One beaker contains salt water, and one contains distilled (or tap) water, but this is unknown to the class.  (experiment with salt to water ratios beforehand to ensure that your egg will float)
• Students are asked the root question below, and are given approx 3 minutes to write down an explanation.
• Students then take another 3 min to discuss their answers with their table groups.
• Students discuss their guesses as a class.
• The teacher then places one egg in each beaker.
• The egg in the distilled water will sink, while the egg in the salt water will float. 
• Repeat steps above to illicit student explanations.
• Manipulate materials as needed to demonstrate the validity of student responses.

Why?

• The salt water has a greater density than the egg, while the distilled water have a lower density than the egg.
• By adding salt to the water, the density is increased.  The salt represents more matter per unit of volume. 
• Eggs work well for this demonstration because they have a density that is between distilled water and salt water. 

 

B.  Raw vs. Cooked
How?

• Take one hard boiled egg and one raw egg.
• Pass the eggs to students so that they can verify that there is no obvious difference.
• Tell the class that you would be will to break only one egg over your head…Ask them how you should decide.  (hint: you might want to tell them that you are looking for the hard-boiled egg)
• Brainstorm a list of methods you could use for checking the egg. 
• Before trying others, tell the students that you can pick out the hard-boiled one just by standing the eggs on their ends.  (If you are brave and have some patience)

Why?

• The raw egg will stand on its bottom and the cooked egg will not.
• This is because the raw yolk (liquid) has more of an ability to move around and re-establish its center of gravity.
• The molecules in the cooked egg (solid) are fixed in place and cannot compensate for gravitational changes. 

 

B. How do you tell the difference between

a raw and a hard-boiled egg?