Year 11 Chemistry: Acids, Bases, and Collision Theory

Comprehensive vocabulary flashcards covering the fundamental concepts, definitions, and terminology of acids, bases, pH, titration, collision theory, and reaction kinetics.

Acid

A substance with a sour taste that produces hydrogen ions ($H^+$) when dissolved in water.

Base

A substance that can neutralise an acid.

Alkali

A base that dissolves in water.

Indicator

A dye that changes colour depending on whether it is in an acid or a base.

pH Scale

A scale that measures how acidic or basic a solution is, usually over the range $0$ to $14$, where each step of one unit represents a ten-fold change in acidity.

Salt

The ionic compound formed when the hydrogen of an acid is replaced by a metal (or ammonium) ion.

Neutralisation

A chemical reaction in which an acid reacts with a base (a metal oxide or metal hydroxide) to produce a salt and water only.

Spectator Ion

An ion that appears unchanged on both sides of a chemical equation, meaning it is present in the mixture but takes no part in the reaction.

Acidic Oxide

A non-metal oxide that usually dissolves in water to form an acid (for example, $CO_2$ or $SO_3$).

Basic Oxide

A metal oxide that usually reacts as a base (for example, $Na_2O$).

Amphoteric Substance

A substance that can act as both an acid and a base depending on what it reacts with, such as water, aluminium oxide ($Al_2O_3$), or zinc hydroxide ($Zn(OH)_2$).

Arrhenius Acid

A substance that produces hydrogen ions ($H^+$) when it dissolves in water.

Arrhenius Base

A substance that produces hydroxide ions ($OH^-$) when it dissolves in water.

Hydronium Ion ($H_3O^+$)

The ion formed when a bare hydrogen ion ($H^+$), which is too reactive to exist alone in water, bonds to a water molecule.

Strong Acid

An acid that ionises completely (essentially $100\%$) in water, meaning almost all of its molecules become ions.

Weak Acid

An acid that ionises only partially in water, so that at any moment only a small fraction of its molecules are ions and the rest remain as whole molecules.

Electrolyte

A solution that conducts electricity because it contains mobile dissolved ions.

Monoprotic Acid

An acid that can release only one hydrogen ion ($H^+$) per molecule (for example, $HCl$ or $HNO_3$).

Polyprotic Acid

An acid that can release more than one hydrogen ion ($H^+$) per molecule in separate stepwise ionisations (for example, diprotic $H_2SO_4$ or triprotic $H_3PO_4$).

Acid Salt

A salt produced by the partial neutralisation of a polyprotic acid that still contains a replaceable hydrogen atom (such as $NaHSO_4$ or $NaHCO_3$).

Self-Ionisation of Water

The reversible process in which one water molecule transfers a hydrogen ion to another to produce hydronium and hydroxide ions: $2H_2O(l) \rightleftharpoons H_3O^+(aq) + OH^-(aq)$.

Ionic Product of Water ($K_w$)

The equilibrium constant defined by $K_w = [H^+][OH^-]$, equal to $1.0 \times 10^{-14}$ at $25\,^{\circ}\text{C}$.

Titration

A volumetric analysis technique used to measure an unknown solution concentration by reacting it with an accurately known standard solution.

Standard Solution

A solution whose concentration is known accurately, used in titrations to determine the concentration of an unknown solution.

Equivalence Point

The point during a titration when the acid and base have been mixed in exactly the mole ratio shown by the balanced chemical equation.

End Point

The moment during a titration when the indicator changes colour.

Concordant Titres

Titre volumes obtained from repeated titration trials that agree within $0.10\,\text{mL}$ of each other.

Rate of Reaction

The change in the amount of a reactant or product per unit of time.

Average Rate

The total change in the amount of reactant or product divided by the total time taken.

Instantaneous Rate

The reaction rate at a single specific moment, found from the gradient of the tangent to the amount-versus-time curve at that point.

Initial Rate

The gradient of the reaction curve at the very start ($t = 0$), which allows fair comparison between conditions before concentrations change.

Collision Theory

A model that explains reaction rates based on the principle that chemical reactions occur when reacting particles collide with sufficient energy and correct orientation.

Successful Collision

A collision between reactant particles that satisfies both having energy equal to or greater than the activation energy ($E_a$) and possessing the correct orientation.

Activation Energy ($E_a$)

The minimum amount of energy that colliding particles must possess for a chemical reaction to occur.

Activated Complex (Transition State)

A brief, highly unstable arrangement of atoms at the top of the energy barrier where existing bonds are partly broken and new bonds are partly formed.

Enthalpy Change ($\Delta H$)

The difference between the chemical potential energy of the products and that of the reactants in a chemical reaction.

Maxwell-Boltzmann Distribution

A graph plotting the number of particles against their kinetic energy, illustrating the spread of energies present in a sample at a given temperature.

Catalyst

A substance that increases the rate of a chemical reaction by providing an alternative reaction pathway with a lower activation energy, without being used up in the process.

Homogeneous Catalyst

A catalyst that exists in the same physical state as the reactants.

Heterogeneous Catalyst

A catalyst that exists in a different physical state from the reactants, typically a solid acting on gaseous or dissolved reactants.

Adsorption

The process by which reactant particles are attracted and bound onto the surface of a solid catalyst, weakening or breaking their bonds.

Enzyme

A biological catalyst consisting of a large protein molecule that speeds up chemical reactions in living organisms at body temperature.