Water

Lab and Aquarium Safety

1. Is it safe to clean your aquarium and/or perform a water change while your aquarium heater is plugged in?
   No, because it can cause electrocution.

2. Can fish and other aquatic organisms transfer bacteria to humans?
   Yes, some can carry bacteria and parasites harmful to humans (like Salmonella).

3. When performing aquarium maintenance, what two things should you not do on the same day?
   Don’t clean the filter and change the water on the same day (removes too many beneficial bacteria).

4. What safety equipment should you wear during a lab experiment? What should you not wear?
   Wear: goggles, gloves, closed-toe shoes.
   Do not wear: loose clothing, dangling jewelry, or open shoes.

Water Distribution

5. What percent of the Earth is covered in water?
   ~71%.

6. What percent of all the water on Earth is saltwater?
   ~97%.

7. What percent of the water on Earth is available for human use?
   Less than 1%.

8. What percent of the human body is made of water?
   ~60–70%.

9. Define hydrosphere.
   All the water on Earth (oceans, lakes, rivers, groundwater, glaciers, atmosphere).

Water Properties: Cohesion, Adhesion, Polarity, Surface Tension

10. Definitions:
    a. Polar – A molecule with an uneven distribution of charge (positive and negative ends).
    b. Nonpolar – A molecule with even charge distribution, no poles.
    c. Adhesion – Attraction between water molecules and other substances.
    d. Cohesion – Attraction between water molecules themselves.
    e. Surface Tension – A “skin-like” surface formed by cohesion of water molecules.
    f. Transpiration – Process of water movement through plants and evaporation from leaves.
    g. Capillary Action – Movement of water through narrow spaces due to cohesion and adhesion.

11. What is electronegativity?
    The tendency of an atom to attract electrons in a bond.

12. How do hydrogen bonds work within water molecules? Is it an inter- or intra-molecular force?
    Hydrogen bonds are intermolecular forces (between water molecules, not within a single one).

Water Chemistry: Heat Capacity and Density

13. What is meant by “water has a very high heat capacity”?
    Water can absorb and store large amounts of heat without a big change in temperature. This moderates Earth’s climate.

Density

14. Order from least dense to most dense:
    Ice → Hot Water → Warm Water → Room Temperature Water → Cold Water
    (a, c, d, e, b).

15. If 10 mL of hot water is dropped into room-temperature water, what will it do?
    It will rise to the top (hot water is less dense).

16. Why does ice float?
    Because hydrogen bonding makes ice less dense than liquid water (molecules spread apart into a crystal lattice).

17. What must happen to the average molecular motion to raise water temperature?
    Molecules must move faster (increase kinetic energy).

18. What is a thermocline? At what latitudes is there an absence of a thermocline?
    A thermocline is a layer in water where temperature changes rapidly with depth. Absent at the poles (polar regions).

19. What are the benefits of water acting as a large heat sink?
    It regulates climate, stabilizes ecosystems, and protects aquatic life from extreme temperature swings.

21. What is Archimedes’ Principle?
    The buoyant force on an object is equal to the weight of the fluid it displaces.

22. What two forces act on flotation?
    Gravity (weight pulling down) and Buoyant force (pushing up).