MCAT CHEM/PHYS
Acid-Base Chemistry Flashcards
30 acid-base terms MCAT Chem/Phys passages assume you already hold
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All 30 MCAT CHEM/PHYS Acid-Base Chemistry flashcards
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- Acid Dissociation Constant (Ka)
- The equilibrium constant for a weak acid ionizing in water, calculated as the concentration of products over reactants at equilibrium, and used to quantify exactly how far that ionization proceeds.For example: Acetic acid's Ka near 1.8 x 10^-5 tells you it barely ionizes compared with a strong acid.
- Amphoteric Solvent
- A solvent molecule that, like water, can itself act as either a proton donor or a proton acceptor depending on what it reacts with, which is why water can be both an acid and a base in different reactions.For example: Water accepts a proton from HCl but donates one to ammonia, switching roles depending on its partner.
- Analyte
- The solution whose concentration is unknown and is being determined by reacting it with a titrant of known concentration.For example: The vinegar sample sitting in the flask underneath the buret is the analyte.
- Anion Gap
- A calculated value found by subtracting the sum of measured blood anions from measured cations, used to narrow down which process is behind a case of metabolic acidosis.For example: An unusually large anion gap points toward an accumulating unmeasured acid, such as lactic acid or ketone bodies.
- Arrhenius Acid
- A substance that, when dissolved in water, raises the concentration of hydrogen ions in the solution, the earliest and narrowest of the three classical acid definitions.For example: Dissolving hydrochloric acid gas in water counts as an Arrhenius acid, but the same gas reacting directly with ammonia does not.
- Autoionization of Water
- The reaction of water molecules with each other to form small equal amounts of hydronium and hydroxide ions, governed by the constant Kw, which equals 1.0 x 10^-14 at 25 degrees Celsius.For example: Even pure, uncontaminated water contains a tiny population of H3O+ and OH- from this self-reaction.
- Base Dissociation Constant (Kb)
- The equilibrium constant describing how completely a weak base picks up a proton from water, playing the same role for bases that Ka plays for acids.For example: Ammonia's small Kb reflects that most ammonia molecules in solution remain unprotonated.
- Bronsted-Lowry Acid
- Any species capable of transferring a hydrogen ion to another substance during a reaction, a definition that applies whether or not the reaction happens in water.For example: Hydrogen chloride gas reacting with ammonia gas transfers a proton with no solvent present at all.
- Bronsted-Lowry Base
- Any species that accepts a hydrogen ion in a reaction, using an available lone pair to bond the incoming proton.For example: The nitrogen lone pair on ammonia grabs a proton from water to form ammonium.
- Buffer Capacity
- The quantity of added acid or base a buffer solution can absorb before its pH begins to shift noticeably, largest when the weak acid and conjugate base are present in roughly equal amounts.For example: A buffer made from large stockpiles of acetic acid and acetate resists pH change over a much bigger range of added acid than a dilute one.
- Buffer Region
- The flat, gently sloping stretch of a titration curve where added acid or base changes the pH only slightly, occurring where meaningful amounts of both the weak acid and its conjugate base coexist.For example: On an acetic acid titration curve, the buffer region spans roughly two pH units centered on the acid's pKa.
- Common-Ion Effect
- The suppression of a weak electrolyte's ionization that occurs when a second, soluble compound sharing one of its ions is added to the same solution, pushing the equilibrium back toward the un-ionized form.For example: Adding sodium acetate to a solution of acetic acid lowers the acid's own ionization because both supply acetate ion.
- Conjugate Acid
- The species left behind once a base has accepted a hydrogen ion, meaning every base has a matching conjugate acid one proton heavier than itself.For example: Ammonia accepting a proton produces ammonium, its conjugate acid.
- Hydronium Ion (H3O+)
- The species that actually forms when a proton attaches to a water molecule, representing what free H+ really looks like in aqueous solution rather than an isolated bare proton.For example: Chemists write H+ as shorthand, but the species measured by a pH probe in water is H3O+.
- Isoelectric Point (pI)
- The specific pH at which an amino acid or protein carries no net electric charge overall, because its positively and negatively charged groups exactly balance.For example: Below its isoelectric point an amino acid carries a net positive charge, and above it a net negative charge.
- Leveling Effect
- The phenomenon by which every strong acid appears equally strong once dissolved in a given solvent, because each one ionizes completely and the solvent's own conjugate base sets the effective acidity ceiling.For example: Perchloric, hydrochloric, and nitric acid all behave as equally strong acids in water, even though their intrinsic strengths differ, because water levels them.
- Lewis Base
- A species that donates an electron pair to form a new covalent bond with another atom or ion, the broadest of the three acid-base models because no proton needs to move at all.For example: The oxygen lone pairs on water let it act as a Lewis base toward a metal cation like Fe3+.
- Metabolic Acidosis
- A fall in blood pH driven by a cause outside the lungs, such as excess acid production or loss of bicarbonate, rather than by a breathing problem.For example: Uncontrolled diabetes can produce ketone acids fast enough to cause metabolic acidosis.
- Metabolic Alkalosis
- A rise in blood pH driven by a cause outside the lungs, such as prolonged loss of stomach acid, rather than by a change in breathing.For example: Repeated vomiting removes hydrochloric acid from the stomach and can push blood pH into metabolic alkalosis.
- Neutralization Reaction
- A reaction in which an acid and a base combine to produce water and a salt, generally releasing heat as the products form.For example: Hydrochloric acid reacting with sodium hydroxide yields water and dissolved sodium chloride.
- pOH
- The negative base-ten logarithm of hydroxide ion concentration, related to pH by the fixed relationship pH plus pOH equals fourteen at 25 degrees Celsius.For example: A solution with pH 9 has a pOH of 5, since the two must sum to fourteen.
- Respiratory Acidosis
- A fall in blood pH that results when breathing is too slow or shallow to clear carbon dioxide, letting carbonic acid build up faster than the body can compensate.For example: A patient with severe opioid overdose breathing too slowly can develop respiratory acidosis from trapped CO2.
- Respiratory Alkalosis
- A rise in blood pH caused by breathing too fast or too deeply, which clears carbon dioxide out of the blood faster than the body produces it.For example: Anxiety-driven hyperventilation can push blood pH upward into respiratory alkalosis within minutes.
- Salt Hydrolysis
- The reaction of an ion released by a dissolved salt with water, producing extra hydrogen or hydroxide ions and shifting the solution's pH away from neutral.For example: Ammonium chloride dissolves and its ammonium ion reacts with water, releasing extra hydrogen ions and making the solution acidic.
- Strong Acid
- An acid that ionizes essentially completely in water, so at equilibrium almost no intact acid molecules remain and the reaction is treated as going to completion.For example: Nitric acid dissolved in water leaves virtually no undissociated HNO3 molecules behind.
- Titrant
- The solution of precisely known concentration that is added, usually from a buret, into the sample being tested during a titration.For example: In a titration of vinegar, standardized sodium hydroxide solution is the titrant.
- Titration
- A laboratory technique that measures out a solution of precisely known concentration into a sample of unknown concentration until the reaction between them is complete, letting the unknown be calculated from the volume used.For example: Slowly adding sodium hydroxide from a buret into vinegar until the color changes determines the vinegar's acetic acid concentration.
- Titration Curve
- A plot of a solution's pH against the volume of titrant added during a titration, whose shape, inflection points, and flat regions reveal the acid or base's identity, strength, and pKa.For example: A weak acid titrated with strong base traces an S-shaped curve with a gently sloping middle region and a steep jump near the equivalence point.
- Titration Indicator
- A weak acid or base dye whose two forms have different colors, chosen so its color-change range overlaps the point where the titration reaction is essentially complete.For example: A titration of a weak base with a strong acid needs an indicator that changes color on the acidic side of neutral, unlike one suited to a strong base titration.
- Weak Acid
- An acid that ionizes only partially in water, establishing a true equilibrium between its molecular and ionized forms rather than reacting to completion.For example: In a solution of acetic acid, most molecules stay intact and only a small fraction dissociate into acetate and hydrogen ions.