Study Guide:  Water Quiz - Honors Biology    

Water - What atoms make up a molecule of water and why is it polar?

Atoms: 1 Oxygen atom and 2 Hydrogen atoms H2O

Why it is polar: Oxygen is a "greedy" atom that pulls shared electrons closer to itself than the Hydrogen atoms can. Because negative electrons hang out closer to the oxygen, the oxygen end gets a slightly negative charge and the hydrogen end gets a slightly positive charge. This uneven split makes water a polar molecule (like a magnet with north and south poles).

Know the difference between:

  • Covalent bonds - A strong chemical bond where two atoms share electrons to stay connected.

  • Polar covalent bonds - A covalent bond where the sharing is unequal (one atom pulls harder on the electrons). This happens inside a single water molecule between the oxygen and hydrogen atoms.

  • Hydrogen Bonds - A weak attraction between separate polar molecules. The slightly positive hydrogen of one water molecule sticks to the slightly negative oxygen of a neighbor.

  • Solvent: The liquid that does the dissolving 

  • Solute: The stuff that gets dissolved 




Explain the 6 properties of water:

  1. Good solvent - Water easily dissolves many substances

  2. High Heat capacity - Retains more heat

  3. Evaporative Cooling - Water evaporates the hottest water molecules leaving the surface cooler (like how we sweat)

  4. Capillary action - When a liquid moves through a narrow space due to Adhesion cohesion and surface tension

  • Cohesion - Lets water stick to water

  • Adhesion - Lets water stick to other surfaces

  1. Surface tension - Strength of liquids to resist external forces

  2. Ice is less dense than water - When liquid water freezes, hydrogen bonds spread out into a rigid frame, pushing the molecules further apart. Because the molecules are less crowded in ice, ice floats on top of liquid water.



How does water moderate temperature?

Water acts as a heat shield for Earth and living things. Thanks to its high heat capacity, oceans absorb massive amounts of heat during hot days or summer months without warming up too fast, and slowly release that heat when it gets cold.



Fill in the pH Scale:  Acidic<7(Neutral)>Basic



Defines and be able to give examples of each:

  • Neutral

Water

  • Acid

Battery

  • Base 

Bleach



Know the difference between strong and weak acids and bases on the pH scale.

Strong Acids (pH 0–3): Break down completely in water to dump a huge amount of H+ ions.

Weak Acids (pH 4–6): Only release a small amount of H+ ions in water (like milk or tomato juice).

Weak Bases (pH 8–10): Only grab a few H+ions (like baking soda or seawater).

Strong Bases (pH 11–14): Grab tons of H+ ions or release lots of OH- ions. Also very harsh and dangerous!




Explain what a buffer does.

A buffer is a biological chemical helper that prevents crazy spikes or drops in pH. If a system gets too acidic, the buffer soaks up extra H+ ions; if it gets too basic, the buffer releases H+ ions. Buffers keep living things alive by maintaining homeostasis