Solution Chemistry & Beer's Law Vocabulary (Lecture Notes)

Vocabulary flashcards covering pH concepts, hydronium, acid/base ranges, Beer's Law, calibration curves, dilution, and spectrophotometry basics from the lecture notes.

pH

A measure of how acidic or basic a solution, defined as the negative logarithm of the hydrogen (hydronium) ion concentration: pH = -log[H+].

Hydronium ion

H3O+, the positively charged species formed when a proton attaches to water; its concentration [H3O+] is used in pH calculations.

Acidic pH range

pH from 0 to 6.9; solutions with pH in this range are considered acidic.

Basic pH range

pH of 7.1 or higher; solutions in this range are basic (alkaline).

Neutral pH

pH = 7.0; the solution is neither acidic nor basic; pure water at standard conditions.

Inverse log

The operation of raising 10 to a power to reverse a logarithm; used to compute [H+] from pH or concentrations from pH.

Absorbance (A)

A dimensionless quantity measured by a spectrophotometer; proportional to concentration for a fixed path length and wavelength according to Beer's Law.

Path length (b)

The distance that light travels through the sample in a cuvette; typically 1 cm in standard measurements.

Beer's Law

A = a b c (often written A = ε b c); A is absorbance, a (or ε) is the molar absorptivity or slope, b is path length, and c is concentration.

Slope (a/ε)

In Beer's Law context, the proportionality constant relating absorbance to concentration for a fixed path length; often equal to molar absorptivity ε.

Calibration curve

A plot of absorbance versus molarity that should be linear; its slope relates absorbance to concentration and is used to determine unknown concentrations from absorbance.

Concentration (c)

Molarity (mol/L) of a solution; the quantity solved for in Beer's Law given absorbance, path length, and slope.

Molar absorptivity (ε)

A constant that relates absorbance to concentration and path length in Beer's Law; sometimes denoted ε; in the notes it is represented as the slope a.

Dilution

Process of adding solvent to decrease solute concentration; results in lower absorbance and is used to generate calibration data.

Wavelength in spectrophotometry

The light wavelength used for measurement (e.g., 590 nm); absorbance depends on wavelength, though Beer's Law relates A to c for a fixed wavelength.

Concentration from absorbance

From Beer's Law A = a b c, solve for c: c = A / (a b); with a and b known, unknown concentration is found from measured absorbance.

Sig figs in Beer's Law problems

Number of significant figures in calculated concentrations should reflect the precision of the absorbance measurement and inputs.