APbio chapter 3
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51 Terms
Why is water a polar molecule?
Oxygen attracts shared electrons more strongly than hydrogen, giving oxygen a partial negative charge and the hydrogens partial positive charges.
What type of bond holds the hydrogen and oxygen atoms together within water?
Polar covalent bonds.
What type of attraction forms between neighboring water molecules?
Hydrogen bonds.
What is a hydrogen bond in water?
An attraction between the partially positive hydrogen of one water molecule and the partially negative oxygen of another.
What is cohesion?
The attraction between molecules of the same substance.
What is adhesion?
The attraction between molecules of different substances.
Why does water have strong cohesion?
Hydrogen bonds attract neighboring water molecules.
What is surface tension?
A measure of how difficult it is to stretch or break the surface of a liquid because of cohesion.
How does cohesion help water move through plants?
Water molecules pull on one another as water moves through the plant's water-conducting tissues.
How does adhesion help water move through plants?
Water molecules are attracted to the walls of the plant's water-conducting tissues.
What is kinetic energy?
Energy associated with the motion of an object or particles.
What is temperature?
A measure of the average kinetic energy of the particles in a substance.
What is a calorie?
The amount of energy required to raise the temperature of 1 gram of water by 1 degree Celsius.
What is specific heat?
The amount of heat required to raise the temperature of 1 gram of a substance by 1 degree Celsius.
Why does water have a high specific heat?
Much of the absorbed energy is used to disrupt hydrogen bonds before water molecules increase their kinetic energy.
How does water's high specific heat benefit organisms?
It helps stabilize temperatures in organisms and their environments.
Why do coastal areas often have milder temperatures than inland areas?
Large bodies of water absorb and release heat slowly because of water's high specific heat.
What is heat of vaporization?
The amount of heat required to convert a liquid into a gas.
Why does water have a high heat of vaporization?
Hydrogen bonds must be overcome for water molecules to escape into the gas phase.
What is evaporative cooling?
Cooling that occurs when the highest-energy molecules escape from a liquid during evaporation.
How does sweating cool the body?
Evaporation of sweat absorbs heat from the skin.
Why does evaporation cool a surface?
The molecules that escape carry away energy, lowering the average kinetic energy of the remaining molecules.
Why does ice float on liquid water?
Ice forms a hydrogen-bonded crystal structure that spaces water molecules farther apart, making ice less dense.
Why is floating ice important for aquatic life?
It insulates the water below, helping aquatic organisms survive in cold conditions.
What is a solution?
A homogeneous mixture of one or more dissolved substances in a solvent.
What is a solvent?
The substance that dissolves another substance.
What is a solute?
The substance dissolved in a solvent.
Why is water an effective solvent for ionic and polar substances?
Its partial charges attract ions and polar molecules.
What is an aqueous solution?
A solution in which water is the solvent.
What is a hydration shell?
A group of water molecules surrounding a dissolved ion or other polar particle.
How does water form a hydration shell around a positive ion?
The partially negative oxygen ends of water molecules orient toward the positive ion.
How does water form a hydration shell around a negative ion?
The partially positive hydrogen ends of water molecules orient toward the negative ion.
What does hydrophilic mean?
Having an affinity for water, often because a substance is charged or polar.
What does hydrophobic mean?
Lacking an affinity for water, often because a substance is nonpolar.
Why do oils separate from water?
Nonpolar oil molecules do not form favorable interactions with polar water molecules.
What is a hydronium ion?
H3O+, formed when a water molecule accepts a proton.
What is a hydroxide ion?
OH−, formed when a water molecule loses a proton or through related reactions in water.
What happens when water molecules dissociate?
A water molecule transfers a proton to another water molecule, producing hydronium and hydroxide ions.
What is an acid?
A substance that increases the hydrogen ion concentration in a solution, commonly by donating protons.
What is a base?
A substance that accepts protons or reduces the hydrogen ion concentration in a solution.
What does the pH scale measure?
How acidic or basic a solution is, based on its hydronium ion concentration.
What is the approximate pH of a neutral solution at 25°C?
7.
What is the pH range of an acidic solution?
Below 7 at 25°C.
What is the pH range of a basic solution?
Above 7 at 25°C.
What happens to hydronium concentration when pH decreases by one unit?
Hydronium concentration increases tenfold.
What happens to hydronium concentration when pH increases by one unit?
Hydronium concentration decreases tenfold.
What is the pH equation?
pH = −log10[H3O+], where the brackets represent hydronium concentration in molarity.
What is a buffer?
A substance or system that resists changes in pH by accepting or donating protons.
How does a buffer resist a drop in pH?
It accepts excess protons.
How does a buffer resist a rise in pH?
It donates protons when needed.
Why are buffers important in living organisms?
They help maintain a stable pH for biological molecules and chemical reactions.