Question

20 questions: wonderfully weird water
analysis:

1. what is the difference between adhesion and cohesion?

1. how was adhesion demonstrated in this lab activity?

1. how was cohesion demonstrated in this lab activity?

1. name a substance that will not dissolve in water and explain why.

1. why is water called the \universal solvent?\

1. what property of water does the water strider (an insect) depend on as it stands and moves across the water’s surface?

1. water is sticky; give me two everyday examples not used in class.

1. challenge yourself: when salt is added to water, the freezing point decreases. why?

Explanation:

1. Defines the two water properties by their interaction targets.
2. Notes a common lab demonstration of adhesion (capillary action in glass).
3. Notes a common lab demonstration of cohesion (surface tension with a needle).
4. Uses oil as an example, explaining polarity incompatibility with water.
5. Explains water's polarity allows it to dissolve most polar/ionic substances.
6. Identifies the property that creates a surface "skin" for water striders.
7. Provides everyday examples of water's adhesive/cohesive "stickiness".
8. Explains how salt disrupts water's ability to form ice crystals.

Answer:

1. Cohesion is attraction between identical water molecules; adhesion is attraction between water molecules and different substances.
2. A common demonstration is water climbing up the inside of a narrow glass tube (capillary action), where water adheres to the glass surface.
3. A common demonstration is floating a small needle on the surface of water, where cohesive forces between water molecules create surface tension that supports the needle.
4. Oil: Water is a polar molecule, while oil is nonpolar. Polar and nonpolar substances do not interact well (like dissolves like rule), so oil does not dissolve in water.
5. Water is called the "universal solvent" because its polar nature allows it to dissolve a wide range of polar and ionic substances, more than most other liquids.
6. The water strider depends on surface tension, a property caused by the cohesive forces between water molecules that creates a rigid, elastic-like surface layer.
7. 1) Water droplets sticking to the side of a drinking glass; 2) A wet paper towel clinging to a countertop.
8. When salt is added to water, the salt ions (Na⁺ and Cl⁻ for table salt) interfere with the ability of water molecules to form the ordered, hexagonal crystal structure of ice. This requires a lower temperature for the water molecules to slow down enough to form ice, thus lowering the freezing point.