Water and Its Biological Properties

Flashcards covering the chemical properties of water, its role as a solvent, temperature moderation, the pH scale, and biological buffers based on lecture notes.

What defines a water molecule as a polar molecule?

The unequal sharing of $e^-$ between oxygen ($O$) and hydrogen ($H$).

What is a hydrogen bond in the context of water molecules?

A bond formed when a slightly negative $O$ is attracted to the slightly positive $H$ of a nearby molecule.

What is the maximum number of hydrogen bonds a single $H_2O$ molecule can form?

$$4$$

Define Cohesion in the context of water.

Hydrogen bonding between like molecules ($H$-bonding between $H_2O$ molecules).

What is Surface Tension?

A measure of how difficult it is to break or stretch the surface of a liquid.

What is Adhesion, and how does it benefit plants?

Adhesion is bonding between unlike molecules; the adhesion of $H_2O$ to vessel walls helps counter the downward pull of gravity.

How do water molecules move up plants during Transpiration?

Water molecules cling to each other via cohesion and cling to xylem tubes via adhesion.

What is the definition of specific heat?

The amount of heat energy required to raise the temperature of a unit mass of a substance by one degree.

What is the biological significance of water's high specific heat for humans?

Since humans are approximately $65\%$ $H_2O$, it helps them maintain a stable temperature and resist temperature changes.

Explain the process of Evaporative Cooling.

Water has a high heat of vaporization; as it evaporates, molecules with the greatest kinetic energy ($KE$) leave as gas, cooling the remaining surface.

Why is ice floating significant for life in ponds or oceans?

Ice is less dense than liquid water, so it floats and insulates the liquid $H_2O$ below, allowing life to exist under the frozen surface.

In a solution, distinguish between the solvent and the solute.

The solvent is the dissolving agent (liquid), while the solute is the substance that is dissolved.

What does the term 'hydrophilic' mean, and what is an example?

Hydrophilic means having an affinity for $H_2O$; examples include polar molecules and ions like cellulose, sugar, and salt.

What does the term 'hydrophobic' mean, and what is an example?

Hydrophobic means repelling $H_2O$; examples include nonpolar molecules like oils and lipids found in cell membranes.

Contrast an acid and a base.

An acid increases $H^+$ concentration (e.g., $HCl$), while a base reduces $H^+$ concentration (e.g., $NaOH$).

What is a hydronium ion, and how is it formed?

A hydronium ion ($H_3O^+$) is formed when a water molecule gains a proton ($H^+ + H_2O \rightarrow H_3O^+$).

According to the pH scale, what is the pH of gastric juice and lemon juice?

$$2$$

According to the pH scale, what is the pH of human blood and tears?

Approximately $7$ (Page 14) or specifically $7.4$ (Page 16).

State the formula for calculating pH.

$$pH = -\log([H^+])$$