Properties of Water, Solutions, pH, and Buffers

Vocabulary flashcards covering the chemical properties of water, solutions, acid-base chemistry, the pH scale, and biological buffer systems based on the lecture notes.

Hydrogen Bonding in Water

Weak bonds formed between a nearby partially negative oxygen atom of one water molecule and a partially positive hydrogen atom of another; each $H_2O$ molecule can hydrogen-bond to as many as 4 partners.

Chemical Reaction

A process that makes and breaks chemical bonds, converting reactants into products by rearranging matter without creating or destroying it.

Reactants

The starting materials in a chemical reaction that are converted into products, such as $H_2$ and $O_2$ in the reaction $2H_2 + O_2 \rightarrow 2H_2O$.

Product

The resulting material formed by a chemical reaction, such as $H_2O$ created from hydrogen and oxygen.

Sphere of Hydration

A clustering of water molecules around solute particles that allows them to stay dissolved in water.

Solution

A liquid consisting of a uniform mixture of two or more substances, formed by combining a solute and a solvent.

Solvent

The dissolving agent of a solution.

Solute

The substance that is dissolved within a solution.

Aqueous Solution

A solution in which water ($H_2O$) is the solvent.

Cohesion

The tendency of molecules of the same kind to stick together, which is unusually strong in water and helps plants transport water and nutrients from roots to leaves.

Adhesion

The tendency of two different kinds of molecules to stick together.

Surface Tension

A measure of how difficult it is to break the surface of a liquid; high in water due to hydrogen bonds, allowing organisms like Water Striders to stand on water.

Thermal Energy

The energy associated with the random movement of atoms and molecules.

Heat

Thermal energy in transfer from a warmer body of matter to a cooler body of matter.

Temperature

A measure of the intensity of heat, representing the average speed of molecules in a body of matter.

Evaporative Cooling

The process in which the surface of a liquid cools down as it evaporates because the molecules with the greatest energy leave the surface.

Density of Ice

The structural property where solid water is less dense than liquid water because freezing forces molecules to form stable hydrogen bonds with neighbors, packing them less densely than in liquid state.

Dissolution of Table Salt (NaCl)

The process where positive hydrogen ends of polar water molecules are attracted to negative chloride ions ($Cl^-$) and negative oxygen ends are attracted to positive sodium ions ($Na^+$).

Acid

A substance that donates hydrogen ions ($H^+$) to solutions, resulting in a condition where $[H^+] > [OH^-]$.

Base

A substance that reduces the hydrogen ion concentration of a solution, resulting in a condition where $[H^+] < [OH^-]$.

pH Scale

A scale ranging from 0 (most acidic) to 14 (most basic) that describes how acidic or basic a solution is, where each unit represents a 10-fold change in $[H^+]$ concentration.

Buffer

A substance or solution that minimizes changes in pH by accepting $H^+$ when it is in excess and donating $H^+$ when it is depleted.

Bicarbonate Buffer System

A major physiological buffer system comprising carbonic acid ($H_2CO_3$, a weak acid) and bicarbonate ion ($HCO_3^-$, a weak base) that maintains pH balance through the reversible reaction $CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$.

Phosphate Buffer System

A buffer system involving species such as $HPO_4$ and $H_2PO_4^{2+}$ that minimizes pH changes when acids or bases are added, such as via the reaction $H_2PO_4^{2+} + OH^- \rightarrow HPO_4 + H_2O$.