DAT (Dental Admission Test) General Chemistry Syllabus

In a stoichiometry problem, what is the limiting reagent and how does it determine yield?

The limiting reagent is the reactant that is completely consumed first; it limits the maximum (theoretical) amount of product formed. Excess reagents remain after the reaction.

How is percent yield calculated?

Percent yield = (actual yield / theoretical yield) × 100%.

Name the five common reaction types: synthesis, decomposition, single replacement, double replacement, and combustion. Give the general form of each.

Synthesis: A + B → AB. Decomposition: AB → A + B. Single replacement: A + BC → AC + B. Double replacement: AB + CD → AD + CB. Combustion: hydrocarbon + O2 → CO2 + H2O.

In double-replacement (metathesis) reactions, what drives the reaction forward?

Formation of a precipitate (insoluble solid), a gas, or a weak electrolyte such as water removes ions from solution and drives the reaction.

Define oxidation and reduction in terms of electron transfer (use the mnemonic OIL RIG).

OIL RIG: Oxidation Is Loss of electrons; Reduction Is Gain of electrons. The oxidized species' oxidation number increases; the reduced species' decreases.

In a redox reaction, what are the oxidizing agent and reducing agent?

The oxidizing agent is the species that gets reduced (gains electrons); the reducing agent is the species that gets oxidized (loses electrons).

State the key oxidation-number rules for free elements, monatomic ions, oxygen, and hydrogen.

Free element = 0; monatomic ion = its charge; oxygen = -2 (except -1 in peroxides); hydrogen = +1 with nonmetals (-1 with metals). The sum of oxidation numbers equals the species' overall charge.

State the ideal gas law and identify the value of R with common units.

PV = nRT. R = 0.0821 L·atm/(mol·K) or 8.314 J/(mol·K). Temperature must be in Kelvin.

State Boyle's law, Charles's law, and Gay-Lussac's law.

Boyle: P1V1 = P2V2 (constant T, n). Charles: V1/T1 = V2/T2 (constant P, n). Gay-Lussac: P1/T1 = P2/T2 (constant V, n).

What is the molar volume of an ideal gas at STP, and what is STP defined as?

22.4 L/mol at STP, defined as 0 °C (273.15 K) and 1 atm pressure.

State Dalton's law of partial pressures and Graham's law of effusion.

Dalton: total pressure = sum of partial pressures (P_total = ΣP_i). Graham: rate of effusion ∝ 1/√(molar mass); rate1/rate2 = √(M2/M1).

Under what conditions do real gases deviate most from ideal behavior?

At high pressure and low temperature, where molecular volume and intermolecular attractions become significant.

What is the difference between melting/freezing, vaporization/condensation, and sublimation/deposition?

Melting (solid→liquid)/freezing (liquid→solid); vaporization (liquid→gas)/condensation (gas→liquid); sublimation (solid→gas)/deposition (gas→solid).

What does the triple point and the critical point represent on a phase diagram?

The triple point is the T and P where solid, liquid, and gas coexist in equilibrium. The critical point is the T and P above which the liquid and gas phases become indistinguishable (a supercritical fluid).

How do you define and use molarity (M)?

Molarity = moles of solute / liters of solution (mol/L). It is used to relate solution volume to moles of dissolved substance.

State the dilution equation and what it assumes.

M1V1 = M2V2; it assumes moles of solute are conserved when solvent is added to dilute a solution.

Differentiate molarity, molality, and mole fraction.

Molarity = mol solute / L solution. Molality = mol solute / kg solvent. Mole fraction = mol of component / total mol of all components.

What are colligative properties, and on what do they depend?

Properties that depend on the number (concentration) of solute particles, not their identity: vapor-pressure lowering, boiling-point elevation, freezing-point depression, and osmotic pressure.

State the equations for boiling-point elevation and freezing-point depression, including the van't Hoff factor.

ΔTb = i·Kb·m and ΔTf = i·Kf·m, where i = van't Hoff factor (particles per formula unit), K = molal constant, m = molality.

What is the van't Hoff factor (i) for glucose, NaCl, and CaCl2 (assuming complete dissociation)?

Glucose (nonelectrolyte) i = 1; NaCl i = 2; CaCl2 i = 3.

State the equation for osmotic pressure.

Π = iMRT, where Π = osmotic pressure, i = van't Hoff factor, M = molarity, R = gas constant, T = temperature in Kelvin.

What is enthalpy (ΔH), and what distinguishes an exothermic from an endothermic process?

Enthalpy is heat content at constant pressure. Exothermic releases heat (ΔH < 0); endothermic absorbs heat (ΔH > 0).

State Hess's law.

The total enthalpy change of a reaction is the same regardless of the pathway; ΔH of an overall reaction equals the sum of the ΔH values of the individual steps.

How is the heat absorbed or released by a substance calculated (no phase change)?

q = mcΔT, where m = mass, c = specific heat capacity, and ΔT = change in temperature.

How do you calculate the standard enthalpy of reaction from standard enthalpies of formation?

ΔH°rxn = Σ(n·ΔH°f products) − Σ(n·ΔH°f reactants). ΔH°f of an element in its standard state = 0.

State the first law of thermodynamics and its equation.

Energy is conserved; the internal energy change ΔU (or ΔE) = q + w, where q is heat added to the system and w is work done on the system.

State the second law of thermodynamics in terms of entropy.

The total entropy of the universe always increases for a spontaneous process (ΔS_universe > 0); entropy is a measure of disorder/dispersal of energy.

State the third law of thermodynamics.

The entropy of a perfect crystalline substance is zero at absolute zero (0 K).

State the Gibbs free energy equation and how ΔG predicts spontaneity.

ΔG = ΔH − TΔS. ΔG < 0 = spontaneous; ΔG > 0 = nonspontaneous; ΔG = 0 = equilibrium.

For the four sign combinations of ΔH and ΔS, when is a reaction spontaneous?

ΔH−, ΔS+: always spontaneous. ΔH+, ΔS−: never spontaneous. ΔH−, ΔS−: spontaneous at low T. ΔH+, ΔS+: spontaneous at high T.

What factors increase the rate of a chemical reaction?

Higher reactant concentration, higher temperature, greater surface area, and addition of a catalyst all increase reaction rate.

What is a catalyst, and how does it affect activation energy and equilibrium?

A catalyst speeds up a reaction by providing an alternate pathway with lower activation energy. It is not consumed and does not change ΔG, ΔH, or the position of equilibrium (it speeds both directions equally).

Write the general rate law and define reaction order.

Rate = k[A]^m[B]^n, where k is the rate constant and m, n are the orders with respect to each reactant. Overall order = m + n; orders are determined experimentally, not from stoichiometry.

What is the rate-determining step of a reaction mechanism?

The slowest elementary step in the mechanism; it controls (limits) the overall reaction rate, and the rate law is based on it (and any preceding equilibria).

What is a reaction intermediate, and how does it differ from a transition state?

An intermediate is a species produced in one step and consumed in a later step (it sits in an energy well and can sometimes be isolated). A transition state is the highest-energy configuration at the peak of an energy barrier and cannot be isolated.

State Le Chatelier's principle.

If a system at equilibrium is disturbed by a change in concentration, pressure/volume, or temperature, the equilibrium shifts to partially counteract the disturbance and restore equilibrium.

How is the equilibrium constant expression (Keq) written for aA + bB ⇌ cC + dD, and what is excluded?

Keq = ([C]^c[D]^d)/([A]^a[B]^b). Pure solids and pure liquids (including solvents) are excluded from the expression.

How does the reaction quotient (Q) compared to K predict the direction of reaction?

If Q < K, reaction proceeds forward (toward products); if Q > K, it proceeds in reverse (toward reactants); if Q = K, the system is at equilibrium.

Compare the Arrhenius, Brønsted-Lowry, and Lewis definitions of acids and bases.

Arrhenius: acid produces H+, base produces OH− in water. Brønsted-Lowry: acid is a proton (H+) donor, base is a proton acceptor. Lewis: acid is an electron-pair acceptor, base is an electron-pair donor.

How are pH, pOH, and [H+] related at 25 °C?

pH = −log[H+]; pOH = −log[OH−]; pH + pOH = 14; and [H+][OH−] = Kw = 1.0 × 10^−14.

What is the difference between a strong acid and a weak acid?

A strong acid dissociates completely in water (large/undefined Ka), e.g., HCl, HNO3, H2SO4. A weak acid only partially dissociates (small Ka) and establishes an equilibrium, e.g., acetic acid.

What is a buffer, and what two components is it made of?

A buffer resists changes in pH upon addition of small amounts of acid or base. It consists of a weak acid and its conjugate base (or a weak base and its conjugate acid) in comparable amounts.

State the Henderson-Hasselbalch equation.

pH = pKa + log([A−]/[HA]), where [A−] is the conjugate base and [HA] is the weak acid. When [A−] = [HA], pH = pKa.

In a titration, what occurs at the equivalence point, and how does it differ from the endpoint?

At the equivalence point, moles of added titrant exactly neutralize moles of analyte (stoichiometric). The endpoint is where the indicator changes color, ideally very close to the equivalence point.

What is the pH at the equivalence point for strong acid–strong base, weak acid–strong base, and strong acid–weak base titrations?

Strong-strong: pH = 7. Weak acid–strong base: pH > 7 (basic salt). Strong acid–weak base: pH < 7 (acidic salt).

What is the solubility product constant (Ksp), and how is it written for CaF2 ⇌ Ca2+ + 2F−?

Ksp is the equilibrium constant for dissolution of a sparingly soluble salt. For CaF2: Ksp = [Ca2+][F−]^2.

What is the common-ion effect on solubility?

Adding an ion already present in a slightly soluble salt's equilibrium decreases the salt's solubility (shifts dissolution equilibrium left), per Le Chatelier's principle.

How do you compare Q (ion product) to Ksp to predict precipitation?

If Q > Ksp, a precipitate forms (supersaturated); if Q = Ksp, the solution is saturated (equilibrium); if Q < Ksp, no precipitate forms (unsaturated).

In a galvanic (voltaic) cell, where do oxidation and reduction occur, and which electrode is the cathode/anode charge?

Oxidation occurs at the anode (negative terminal in a galvanic cell); reduction occurs at the cathode (positive terminal). Electrons flow from anode to cathode.

How is the standard cell potential (E°cell) calculated from electrode potentials?

E°cell = E°cathode − E°anode (using standard reduction potentials). A positive E°cell indicates a spontaneous (galvanic) reaction.

How are ΔG° and E°cell related?

ΔG° = −nFE°cell, where n = moles of electrons transferred and F = Faraday's constant (96,485 C/mol). A positive E°cell gives a negative ΔG° (spontaneous).

How do electrolytic cells differ from galvanic cells?

Electrolytic cells use an external power source to drive a nonspontaneous reaction (E°cell < 0, ΔG > 0). Oxidation still occurs at the anode and reduction at the cathode, but the anode is positive and cathode negative (opposite signs vs. galvanic).

What does Faraday's law of electrolysis relate?

The mass of substance produced or consumed at an electrode is proportional to the quantity of electric charge passed (Q = I·t), using moles of electrons (Q/F) and the half-reaction stoichiometry.

Compare alpha, beta, and gamma radiation in terms of composition and penetrating power.

Alpha (α) = helium nucleus (2p, 2n, +2), least penetrating (stopped by paper). Beta (β) = high-speed electron (−1), moderate penetration (stopped by aluminum). Gamma (γ) = high-energy photon (no mass/charge), most penetrating (needs lead/concrete).

How do the atomic number and mass number change during alpha decay and beta-minus decay?

Alpha decay: mass number decreases by 4, atomic number decreases by 2. Beta-minus decay: mass number unchanged, atomic number increases by 1 (a neutron converts to a proton + electron).

What is half-life, and how much of a sample remains after n half-lives?

Half-life is the time for half of a radioactive sample to decay. After n half-lives, the fraction remaining = (1/2)^n of the original amount.

What is the difference between nuclear fission and nuclear fusion?

Fission splits a heavy nucleus into lighter nuclei, releasing energy (e.g., uranium in reactors/bombs). Fusion combines light nuclei into a heavier one, releasing even more energy (e.g., hydrogen fusing in the sun).