Unit 2: Acids, Bases, Salts, Chemical Kinetics & Equilibrium

Flashcards covering Unit 2 Module 1 (Chemical Kinetics & Equilibrium) and Unit 2 Module 2 (Acids, Bases & Salts) from Pharmaceutical Inorganic Chemistry.

According to the lecture, what is an acid and what are its key properties?

An acid is a substance that releases hydrogen ions (protons) or accepts electron pairs. Key properties include a sour taste, a pH $< 7$, reacting with bases in neutralization reactions, reacting with active metals to produce hydrogen gas, and conducting electricity in aqueous solution.

What are three daily life examples of acids given in the lecture?

1. Citric acid (found in fruits)
2. Acetic acid (found in vinegar)
3. Hydrochloric acid ($HCl$, stomach acid)

How is a base defined, and what are its main physical and chemical properties?

A base is a substance that releases hydroxide ions or donates electron pairs. Its properties include a bitter taste, a slippery feel, a pH $> 7$, the ability to neutralize acids, being caustic (capable of causing burns), and conducting electricity in solution.

What are three daily life examples of bases mentioned in the transcript?

1. Sodium hydroxide ($NaOH$, lye used in soap making)
2. Ammonia ($NH_3$, used as a cleaning agent)
3. Magnesium hydroxide ($Mg(OH)_2$, used as an antacid)

What is a salt and what general properties does it exhibit?

A salt is an ionic compound formed when the $H^+$ of an acid is replaced by a metal ion or an ammonium ion. Properties include existing as crystalline solids with high melting points, acting as strong electrolytes (dissociating completely in water), and being neutral, acidic, or basic depending on their origin.

What neutralization reaction produces a salt, and what are three daily life examples of salts?

Formation reaction: $\text{Acid} + \text{Base} \rightarrow \text{Salt} + H_2O$. Daily life examples include table salt ($NaCl$, saline solutions), baking soda ($NaHCO_3$, antacid), and phosphate salts ($KH_2PO_4$, used in IV fluids).

How does the Arrhenius Theory define acids and bases, and what is its main limitation?

Arrhenius Theory states that an acid yields $H^+$ and $H_3O^+$ ions in water solution, while a base yields $OH^-$ ions. Its primary limitation is that it is not applicable to non-aqueous solvents.

What are the definitions of an acid and a base under the Brønsted-Lowry Theory, and what is its advantage over Arrhenius Theory?

A Brønsted-Lowry acid donates a proton ($H^+$), and a Brønsted-Lowry base accepts a proton. Its key advantage is that it explains acid-base behavior in both aqueous and non-aqueous media.

What is a conjugate acid-base pair, and what ion is always formed when an acid dissolves in water?

A conjugate pair consists of an acid and its conjugate base that differ by one proton. When an acid dissolves in water, the hydronium/oxonium ion ($H_3O^+$) is always formed (free $H^+$ is practically non-existent in solution).

How does Lewis Theory define acids and bases?

A Lewis acid accepts an electron pair, while a Lewis base donates an electron pair, forming coordinate covalent bonds.

Why is water omitted from the equilibrium expression when deriving the acid ionization constant ($K_a$)?

Because $H_2O$ is the solvent and present in large excess, its molar concentration remains practically constant, allowing it to be combined with the equilibrium constant: $K_c \times [H_2O] = K_a$.

What is chemical kinetics?

Chemical kinetics is the discipline concerned with the study of reaction rates, the factors that influence these rates, and the mechanism or step sequence by which a chemical process proceeds from its initial state to its final state.

How is the rate of reaction measured, and what constitutes a reaction mechanism?

The rate of reaction is the amount of chemical change occurring in a given interval of time, measured in terms of products formed or reactants lost per unit time at a given temperature. A reaction mechanism is the complete sequence of individual steps (often involving intermediates) through which a reaction occurs.

What are the differences between reversible, simultaneous, and consecutive reactions?

1. Reversible reactions proceed in both forward and backward directions under the same conditions to reach equilibrium.
2. Simultaneous reactions are two or more reactions taking place at the same time using the same reactants or conditions and competing with each other.
3. Consecutive reactions occur stepwise in a series where the product of one step becomes the reactant for the next.

According to Molecular Collision Theory, what two requirements must be satisfied for a collision to produce a chemical reaction?

1. Activation Energy: Colliding molecules must possess a minimum energy required to undergo reaction.
2. Orientation: The orientation of the colliding molecules must be favorable for the making and breaking of bonds.

How do the nature of reactants and temperature affect the rate of a chemical reaction?

Ionic reactions are generally fast (e.g., neutralization) while covalent reactions are slower (e.g., hydrolysis). Higher temperature causes molecules to move faster and collide more frequently; as a general rule, reaction rate approximately doubles for every $10^\text{o}\text{C}$ rise in temperature.

How do positive catalysts (accelerators) differ from negative catalysts (inhibitors)?

A catalyst alters the rate of a chemical reaction without being consumed. Positive catalysts (accelerators) increase the reaction rate, whereas negative catalysts (inhibitors) decrease the rate by interfering with the natural reaction mechanism (e.g., sodium benzoate preservatives in food or antioxidants in oils).

What does the Law of Mass Action state?

The Law of Mass Action states that the speed of a chemical change is directly proportional to the concentration of the reacting substances, as higher concentrations increase molecular collisions per unit time.

What is chemical equilibrium?

Chemical equilibrium is a dynamic state in which the forward and reverse reaction rates are equal, and the concentrations of reactants and products remain constant over time with no net change occurring.

What is the equilibrium constant ($K_c$), and how are different magnitudes of $K_c$ interpreted?

$K_c$ is the ratio of product concentrations to reactant concentrations, each raised to the power of their stoichiometric coefficients at equilibrium. If K_c \boldsymbol{\frac{[NH_3]^2}{[N_2][H_2]^3} = \frac{(0.10)^2}{(0.20)(0.30)^3} = \frac{0.01}{0.0054} \boldsymbol{\frac{[H^+][CH_3COO^-]}{[CH_3COOH]} = \frac{(0.05)(0.05)}{0.45} = 0.0056. The small $K_c$ shows that reactants are favored and acetic acid is a weak acid.

What does Le Chatelier's Principle state?

Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change and reestablish equilibrium.