ACS General Chemistry Exam Practice

Ideal gas law equation relating pressure ($P$), volume ($V$), moles ($n$), and absolute temperature ($T$)

$$PV = nRT$$

Formula for ideal gas density ($d$) in terms of pressure ($P$), molar mass ($M$), and absolute temperature ($T$)

$$d = \frac{PM}{RT}$$

Combined gas law relating pressure ($P$), volume ($V$), and absolute temperature ($T$) across two states of a fixed amount of gas

$$\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}$$

Calorimetry equation for heat transfer ($q$) using mass ($m$), specific heat capacity ($c$), and temperature change ($\Delta T$)

$$q = mc\Delta T$$

Formula for calculating standard reaction enthalpy ($\Delta H^\circ_\text{rxn}$) from standard enthalpies of formation ($\Delta H^\circ_\text{f}$)

$$\Delta H^\circ_\text{rxn} = \sum m\Delta H^\circ_\text{f}(\text{products}) - \sum n\Delta H^\circ_\text{f}(\text{reactants})$$

Gibbs free energy equation relating $\Delta G^\circ$, $\Delta H^\circ$, and $\Delta S^\circ$ at constant temperature ($T$)

$$\Delta G^\circ = \Delta H^\circ - T\Delta S^\circ$$

Thermodynamic equation relating standard Gibbs free energy change ($\Delta G^\circ$) to the equilibrium constant ($K$)

$$\Delta G^\circ = -RT\ln(K)$$

Electrochemical equation relating standard Gibbs free energy change ($\Delta G^\circ$) to standard cell potential ($E^\circ_\text{cell}$)

$$\Delta G^\circ = -nFE^\circ_\text{cell}$$

Nernst equation for operational cell potential ($E_\text{cell}$) at $25\,^\circ\text{C}$ in terms of the reaction quotient ($Q$)

$$E_\text{cell} = E^\circ_\text{cell} - \frac{0.0592}{n}\log(Q)$$

Henderson-Hasselbalch equation for the $\text{pH}$ of an acidic buffer solution

$$\text{pH} = \text{p}K_\text{a} + \log\left(\frac{[\text{A}^-]}{[\text{HA}]}\right)$$

Integrated rate law equation for a first-order chemical reaction of reactant $A$

$$\ln[A]_t = -kt + \ln[A]_0$$

Half-life equation ($t_{1/2}$) for a first-order chemical or radioactive decay process

$$t_{1/2} = \frac{\ln(2)}{k}$$

Equation relating the equilibrium constant in partial pressures ($K_p$) to that in molar concentrations ($K_c$)

$$K_p = K_c(RT)^{\Delta n_\text{gas}}$$

Colligative property formulas for freezing point depression ($\Delta T_\text{f}$) and boiling point elevation ($\Delta T_\text{b}$)

$\Delta T_\text{f} = iK_\text{f}m$ and $\Delta T_\text{b} = iK_\text{b}m$

Formula computing the osmotic pressure ($\Pi$) of a solution containing an electrolyte

$$\Pi = iMRT$$

Plank's constant is $6.626 \times 10^{-34}\,\text{J}\,\text{s}$. What is this value expressed in $\text{kJ}\,\mu\text{s}$?

$$6.626 \times 10^{-31}\,\text{kJ}\,\mu\text{s}$$

When sighting the concave meniscus of a liquid in a graduated cylinder with $1\,\text{cm}^3$ graduations that sits exactly halfway between the $42$ and $43$ marks, what is the correctly reported volume?

$$42.5\,\text{cm}^3$$

What is the systematic chemical name for the ionic compound $\text{FeCO}_3$?

Iron(II) carbonate

What is the chemical formula of iodic acid?

$$\text{HIO}_3$$

What is the systematic IUPAC name for the binary covalent molecular compound $\text{N}_2\text{O}_5$?

Dinitrogen pentoxide

A $28.225\,\text{g}$ sample of an unknown metal placed into a graduated cylinder displaces the water level from $7.75\,\text{cm}^3$ to $11.70\,\text{cm}^3$. What is the density of the metal?

$$7.15\,\text{g}\,\text{cm}^{-3}$$

Which classification describes a uniform physical combination of two or more pure substances lacking any visible boundaries between phases?

Homogeneous mixture (solution)

Which subatomic particle was experimentally verified by James Chadwick in 1932 by bombarding beryllium with alpha particles?

Neutron

How many protons, neutrons, and electrons are present in the titanium(III) cation $^{47}_{22}\text{Ti}^{3+}$?

$22$ protons, $25$ neutrons, and $19$ electrons

Chlorine occurs naturally as two stable isotopes: $^{35}\text{Cl}$ ($34.97\,\text{amu}$) and $^{37}\text{Cl}$ ($36.97\,\text{amu}$). If the average atomic mass is $35.45\,\text{amu}$, what are their relative percent abundances?

$76\%$ $^{35}\text{Cl}$ and $24\%$ $^{37}\text{Cl}$

Which group on the periodic table contains the largest number of naturally occurring diatomic molecular elements?

Group 17

Which monatomic ion possesses the exact same total number of electrons as a neutral argon ($\text{Ar}$) atom?

$$\text{Cl}^-$$

The mass number ($A$) of an atom is defined as the integer sum of which subatomic nuclear particles?

Protons and neutrons

Based on its position in Period 3 and Group 16 of the periodic table, what is the chemical classification of elemental sulfur?

Nonmetal

What is the energy of a single photon having a wavelength of $656\,\text{nm}$?

$$3.03 \times 10^{-19}\,\text{J}$$

According to the Pauli exclusion principle, what is the maximum number of electrons that can occupy a single atomic orbital labeled $d_{xy}$?

$$2$$

What is the total number of allowed atomic orbitals in the $n = 4$ principal energy level of an atom?

$$16$$

What is the complete ground-state electron configuration of a neutral manganese atom ($\text{Mn}$, $Z = 25$)?

$$[\text{Ar}]\,4s^2 3d^5$$

How many unpaired electrons are present in the ground state of an isolated iron(II) cation ($\text{Fe}^{2+}$, $d^6$)?

$$4$$

Among the elements $\text{Li}$, $\text{Ne}$, $\text{Na}$, and $\text{Ar}$, which exhibits the largest first ionization energy?

$$\text{Ne}$$

Which list arranges the isoelectronic species $\text{F}^-$, $\text{Na}^+$, and $\text{Mg}^{2+}$ in order of decreasing ionic radius (largest first)?

$$\text{F}^- > \text{Na}^+ > \text{Mg}^{2+}$$

Why does the atomic radius systematically decrease when moving from left to right across Period 3 of the periodic table?

Effective nuclear charge increases while core electron shielding remains constant

How many individual aluminum atoms are contained in a $1.50\,\text{g}$ sample of pure aluminum metal ($M = 26.98\,\text{g}\,\text{mol}^{-1}$)?

$$3.35 \times 10^{22}\text{ atoms}$$

What is the molar mass of potassium tris(oxalato)ferrate(III), $\text{K}_3\text{Fe}(\text{C}_2\text{O}_4)_3$?

$$437.15\,\text{g}\,\text{mol}^{-1}$$

What mass of elemental carbon is contained in $0.500\,\text{mol}$ of pure sucrose ($\text{C}_{12}\text{H}_{22}\text{O}_{11}$)?

$$72.0\,\text{g}$$

What is the percent composition by mass of oxygen in potassium carbonate ($\text{K}_2\text{CO}_3$, $M = 138.2\,\text{g}\,\text{mol}^{-1}$)?

$$34.73\%$$

Ibuprofen contains $75.7\%$ carbon, $8.80\%$ hydrogen, and $15.5\%$ oxygen by mass. What is its empirical formula?

$$\text{C}_{13}\text{H}_{18}\text{O}_2$$

A molecular compound has an empirical formula of $\text{NO}_2$ and an experimental molar mass of $92.0\,\text{g}\,\text{mol}^{-1}$. What is its molecular formula?

$$\text{N}_2\text{O}_4$$

How many sodium cations ($\text{Na}^+$) are present in $25.0\,\text{g}$ of pure $\text{Na}_2\text{CO}_3$ ($M = 105.99\,\text{g}\,\text{mol}^{-1}$)?

$$2.84 \times 10^{23}\text{ ions}$$

What is the stoichiometric coefficient for $\text{NaCl}$ when $\text{CaCl}_2 + \text{Na}_3\text{PO}_4 \rightarrow \text{Ca}_3(\text{PO}_4)_2 + \text{NaCl}$ is balanced using the lowest whole numbers?

$$6$$

How many moles of $\text{CO}_2$ are produced when $2.50\,\text{mol}$ of ethanol combusts in excess oxygen via $\text{C}_2\text{H}_6\text{O}(l) + 3\text{O}_2(g) \rightarrow 2\text{CO}_2(g) + 3\text{H}_2\text{O}(g)$?

$$5.00\,\text{mol}$$

What mass of ammonia ($\text{NH}_3$, $17.03\,\text{g}\,\text{mol}^{-1}$) is required to form $0.340\,\text{mol}$ of $\text{NO}$ in $4\text{NH}_3 + 5\text{O}_2 \rightarrow 4\text{NO} + 6\text{H}_2\text{O}$?

$$5.79\,\text{g}$$

If $9.0\,\text{mol}$ of $\text{F}_2$ and $4.0\,\text{mol}$ of $\text{S}$ react according to $3\text{F}_2 + \text{S} \rightarrow \text{SF}_6$, how many moles of the excess reactant remain unreacted?

$$1.0\,\text{mol}\,\text{S}$$

When $15.5\,\text{g}$ of $\text{Mg}$ reacts with excess nitrogen to yield $18.2\,\text{g}$ of $\text{Mg}_3\text{N}_2$ (theoretical yield $21.46\,\text{g}$), what is the percent yield?

$$84.8\%$$

What maximum mass of $\text{NO}_2$ ($46.0\,\text{g}\,\text{mol}^{-1}$) can form when $7.50\,\text{g}$ of $\text{N}_2\text{O}_5$ ($108.0\,\text{g}\,\text{mol}^{-1}$) decomposes via $2\text{N}_2\text{O}_5 \rightarrow 4\text{NO}_2 + \text{O}_2$?

$$6.39\,\text{g}$$

Which conceptual definition best describes the limiting reactant in any chemical reaction mixture?

The reactant that is completely consumed first, setting the theoretical limit on product formation

What volume of oxygen gas measured at STP is generated from the complete thermal decomposition of $67.5\,\text{g}$ of $\text{HgO}$ ($216.59\,\text{g}\,\text{mol}^{-1}$) via $2\text{HgO}(s) \rightarrow 2\text{Hg}(l) + \text{O}_2(g)$?

$$3.49\,\text{dm}^3$$

Why is an aqueous solution of ammonia ($\text{NH}_3$) classified as a weak electrolyte?

It ionizes only partially in aqueous solution to establish equilibrium with low concentrations of ions

What mass of solid magnesium nitrate, $\text{Mg}(\text{NO}_3)_2$ ($148.3\,\text{g}\,\text{mol}^{-1}$), is required to prepare $250.0\,\text{cm}^3$ of a $0.0750\,\text{mol}\,\text{dm}^{-3}$ solution?

$$2.78\,\text{g}$$

What is the molar concentration of chloride ions in a $3.0\,\text{mol}\,\text{dm}^{-3}\,\text{CaCl}_2$ aqueous solution?

$$6.0\,\text{mol}\,\text{dm}^{-3}$$

What is the final molarity when $28.2\,\text{cm}^3$ of an $11.8\,\text{mol}\,\text{dm}^{-3}$ stock solution is diluted with pure water to a final volume of $100.0\,\text{cm}^3$?

$$3.33\,\text{mol}\,\text{dm}^{-3}$$

When aqueous solutions of $\text{KI}$, $\text{NaC}_2\text{H}_3\text{O}_2$, and $\text{Pb}(\text{NO}_3)_2$ are mixed, what insoluble precipitate forms?

$$\text{PbI}_2$$

What is the spectator ion in the neutralization reaction between aqueous acetic acid and aqueous sodium hydroxide?

$$\text{Na}^+$$

What is the oxidation number of chromium in sodium dichromate ($\text{Na}_2\text{Cr}_2\text{O}_7$)?

$$+6$$

Identify the oxidizing agent in the redox reaction $2\text{AuCl}_3(aq) + 3\text{H}_2(g) \rightarrow 2\text{Au}(s) + 6\text{HCl}(aq)$.

$$\text{AuCl}_3$$

What is the change in internal energy ($\Delta E$) for a system that absorbs $375\,\text{kJ}$ of thermal energy as heat and performs $125\,\text{kJ}$ of expansion work on its surroundings?

$$+250\,\text{kJ}$$

Two metal samples of equal mass at $25\,^\circ\text{C}$ receive identical thermal energy inputs: sample X ($c = 0.350\,\text{J}\,\text{g}^{-1}\,\text{K}^{-1}$) and sample Z ($c = 0.895\,\text{J}\,\text{g}^{-1}\,\text{K}^{-1}$). Which sample achieves the higher final temperature?

Sample X

Combustion of a $1.00\,\text{g}$ sample of glucose ($180.2\,\text{g}\,\text{mol}^{-1}$, $\Delta H = -2830\,\text{kJ}\,\text{mol}^{-1}$) raises a bomb calorimeter's temperature by $9.40\,^\circ\text{C}$. What is the calorimeter's heat capacity?

$$1.67\,\text{kJ}\,{^\circ}\text{C}^{-1}$$

Which chemical equation correctly depicts the standard enthalpy of formation ($\Delta H^\circ_\text{f}$) of liquid water?

$$\text{H}_2(g) + \frac{1}{2}\text{O}_2(g) \rightarrow \text{H}_2\text{O}(l)$$

How much heat energy is required to completely melt $25.0\,\text{g}$ of ice at $0\,^\circ\text{C}$ ($\Delta H_\text{fus} = 6.01\,\text{kJ}\,\text{mol}^{-1}$, $M = 18.02\,\text{g}\,\text{mol}^{-1}$)?

$$8.34\,\text{kJ}$$

Given $\Delta H^\circ_\text{f}$ values of $\text{C}_2\text{H}_2(g) = +227\,\text{kJ}\,\text{mol}^{-1}$, $\text{CO}_2(g) = -393.5\,\text{kJ}\,\text{mol}^{-1}$, and $\text{H}_2\text{O}(g) = -241.8\,\text{kJ}\,\text{mol}^{-1}$, what is $\Delta H^\circ_\text{rxn}$ for $2\text{C}_2\text{H}_2(g) + 5\text{O}_2(g) \rightarrow 4\text{CO}_2(g) + 2\text{H}_2\text{O}(g)$?

$$-2511\,\text{kJ}\,\text{mol}^{-1}$$

What are the sign of $\Delta H$ and the direction of heat transfer in an endothermic chemical reaction?

$\Delta H > 0$; the system absorbs thermal energy from the surroundings

How much heat is required to react $10.5\,\text{g}$ of iron ($55.85\,\text{g}\,\text{mol}^{-1}$) via $2\text{Fe}(s) + 3\text{CO}(g) \rightarrow \text{Fe}_2\text{O}_3(s) + 3\text{CO}_2(g)$ ($\Delta H^\circ = 26.8\,\text{kJ}\,\text{mol}^{-1}$)?

$$2.52\,\text{kJ}$$

Which ranking lists the ionic solids $\text{NaBr}$, $\text{CaCl}_2$, $\text{MgO}$, and $\text{ScN}$ in order of increasing magnitude of lattice energy?

$$\text{NaBr} < \text{CaCl}_2 < \text{MgO} < \text{ScN}$$

The Pauling electronegativity of carbon is $2.5$ and fluorine is $4.0$. What is the classification of the chemical bond between these two elements?

Polar covalent bond

How many nonbonding lone pairs of electrons are situated on the central chlorine atom in the stable Lewis structure of $\text{ClF}_3$?

$$2$$

How is the reaction enthalpy ($\Delta H_\text{rxn}$) mathematically estimated from gas-phase bond dissociation energies ($D$)?

$$\Delta H_\text{rxn} = \sum D(\text{bonds broken}) - \sum D(\text{bonds formed})$$

How do the bond length and bond strength of an $\text{O}=\text{O}$ double bond compare to an $\text{O}-\text{O}$ single bond?

The double bond is shorter and stronger

What is the molecular geometry of the carbonate polyatomic anion ($\text{CO}_3^{2-}$) predicted by VSEPR theory?

Trigonal planar

What is the orbital hybridization on the central carbon atom in carbon dioxide ($\text{CO}_2$)?

$$sp$$

According to molecular orbital theory, what is the calculated bond order of the helium dimer dication ($\text{He}_2^{2+}$)?

$$1$$

Under what combination of physical conditions does a real gas show the greatest deviation from ideal gas behavior?

High pressure and low temperature

A sample of ideal gas occupies $3.00\,\text{dm}^3$ at $1.00\,\text{atm}$. What volume does it occupy at $1.45\,\text{atm}$ at identical temperature?

$$2.07\,\text{dm}^3$$

In a gas mixture containing $3.25\,\text{mol}$ of $\text{O}_2$ and $2.75\,\text{mol}$ of $\text{N}_2$ at a total barometric pressure of $22.4\,\text{atm}$, what is the partial pressure of $\text{O}_2$?

$$12.1\,\text{atm}$$

How does the root-mean-square speed ($u_\text{rms}$) of gas particles depend on molar mass ($M$) at constant absolute temperature?

It is inversely proportional to the square root of the molar mass

Why is the normal boiling point of liquid bromine ($\text{Br}_2$) substantially higher than that of chlorine ($\text{Cl}_2$)?

Bromine is more polarizable due to its larger electron cloud, generating stronger London dispersion forces

How many net metal atoms are contained within a single face-centered cubic (FCC) unit cell?

$$4$$

How is solid silicon dioxide ($\text{SiO}_2$), which possesses a three-dimensional lattice of tetrahedral silicon atoms bound to bridging oxygens, classified?

Covalent-network solid

What is the thermodynamic term for the direct, exothermic phase transition of a substance from a gas to a solid?

Deposition

Which specific intermolecular force explains why ethanol ($\text{CH}_3\text{CH}_2\text{OH}$) is completely miscible in liquid water in all proportions?

Hydrogen bonding between the hydroxyl groups and water molecules

What is the molality of an aqueous solution prepared by dissolving $25.0\,\text{g}$ of $\text{NaOH}$ ($40.0\,\text{g}\,\text{mol}^{-1}$) into $300.0\,\text{g}$ of pure water?

$$2.08\,\text{mol}\,\text{kg}^{-1}$$

According to Henry's law, how does increasing the temperature influence the aqueous solubility of a gas at constant partial pressure?

Gas solubility decreases

According to Raoult's law, how does dissolving a nonvolatile solute into a volatile solvent affect the solvent's equilibrium vapor pressure?

It lowers the vapor pressure proportional to the solvent's mole fraction ($P = X_\text{solvent} P^\circ$)

What is the normal boiling point of a $1.24\,m$ aqueous $\text{AlCl}_3$ solution ($i = 4$, $K_\text{b} = 0.512\,^\circ\text{C}\,m^{-1}$)?

$$102.5\,^\circ\text{C}$$

Which $0.10\,m$ aqueous solution exhibits the lowest freezing point: $\text{Al}(\text{NO}_3)_3$, $\text{CaCl}_2$, $\text{NaCl}$, or $\text{C}_2\text{H}_5\text{OH}$?

$$\text{Al}(\text{NO}_3)_3$$

Which formula correctly computes the osmotic pressure ($\Pi$) of a solution containing an electrolyte?

$$\Pi = iMRT$$

What term describes a metastable solution that contains a dissolved solute concentration greater than its thermodynamic saturation equilibrium value?

Supersaturated

If doubling the initial concentration of reactant $A$ quadruples the initial rate while other concentrations remain unchanged, what is the reaction order with respect to $A$?

Second order

What are the dimensional units of the rate constant ($k$) for an overall second-order chemical reaction with time measured in seconds?

$$\text{dm}^3\,\text{mol}^{-1}\,\text{s}^{-1}$$

For a zero-order decomposition reaction, which graphical plot of kinetic data yields a straight line with a slope equal to $-k$?

$[A]$ versus time

The radioactive decay rate of an isotope drops from $3000\,\text{counts/min}$ to $375\,\text{counts/min}$ over $24.0\,\text{days}$. What is the half-life of this isotope?

$$8.0\,\text{days}$$

Through what mechanism does a chemical catalyst accelerate the rate of a chemical transformation?

It provides an alternative reaction pathway possessing a lower activation energy

What fundamental role does the slowest elementary step play in a proposed multi-step reaction mechanism?

It serves as the rate-determining step and dictates the overall experimental rate law

How is a reaction intermediate defined within a multi-step chemical reaction mechanism?

A chemical species formed in an early elementary step and subsequently consumed in a later step

According to collision theory, what two requirements must colliding reactant molecules satisfy for a collision to produce a reaction?

Sufficient kinetic energy ($\ge E_\text{a}$) and proper spatial orientation