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Chemistry practice questions

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Question 1Physical chemistry, amounts and reactions

What is the mass percent of hydrogen in H2O? (H = 1.0 g mol-1, O = 16.0 g mol-1)

  1. 5.6%
  2. 11% Correct answer.
  3. 33%
  4. 89%

Explanation

M(H2O) = 18.0 g mol-1. Mass percent H = (2.0/18.0) x 100% is about 11%.

Question 2Physical chemistry, amounts and reactions

In the balanced equation for aluminium combustion, 4 Al + 3 O2 -> 2 Al2O3, what is the coefficient of O2?

  1. 1
  2. 2
  3. 3 Correct answer.
  4. 4

Explanation

The smallest-integer balanced equation is 4 Al + 3 O2 -> 2 Al2O3, so the O2 coefficient is 3.

Question 3Physical chemistry, amounts and reactions

How many moles of ideal gas occupy 22.4 L at STP if the molar volume is 22.4 L mol-1?

  1. 0.50 mol
  2. 1.0 mol Correct answer.
  3. 2.0 mol
  4. 22.4 mol

Explanation

At STP the molar volume is 22.4 L mol-1, so 22.4 L corresponds to 1.0 mol of ideal gas.

Question 4Physical chemistry, amounts and reactions

In 2 H2 + O2 -> 2 H2O, if 4.0 mol H2 reacts with excess O2, how many moles of H2O form?

  1. 2.0 mol
  2. 4.0 mol Correct answer.
  3. 6.0 mol
  4. 8.0 mol

Explanation

The mole ratio H2:H2O is 2:2 = 1:1, so 4.0 mol H2 produces 4.0 mol H2O.

Question 5Physical chemistry, amounts and reactions

What is the pH of 0.010 M aqueous HCl at 25 C (strong acid, complete dissociation)?

  1. 0.010
  2. 1.0
  3. 2.0 Correct answer.
  4. 12

Explanation

For a strong monoprotic acid, [H3O+] = 0.010 M = 1.0 x 10^-2 M. pH = -log(1.0 x 10^-2) = 2.0.

Question 6Physical chemistry, amounts and reactions

You dilute 25.0 mL of 2.00 M HCl to a final volume of 100.0 mL. What is the final concentration?

  1. 0.250 M
  2. 0.500 M Correct answer.
  3. 2.00 M
  4. 8.00 M

Explanation

M1V1 = M2V2 gives M2 = (2.00 M x 25.0 mL) / 100.0 mL = 0.500 M.

Question 7Physical chemistry, amounts and reactions

A compound is 40.0% C, 6.7% H and 53.3% O by mass. Its empirical formula is

  1. CHO
  2. CH2O Correct answer.
  3. C2H4O2
  4. C2H6O

Explanation

Assume 100 g: 40.0 g C -> 3.33 mol; 6.7 g H -> 6.7 mol; 53.3 g O -> 3.33 mol. Divide by 3.33 to get C1H2O1, so CH2O. C2H4O2 is a molecular multiple of CH2O.

Question 8Physical chemistry, amounts and reactions

For 2 H2 + O2 -> 2 H2O, if 3.0 mol H2 and 3.0 mol O2 are mixed, which reactant is limiting?

  1. H2 Correct answer.
  2. O2
  3. H2O
  4. Neither; both are limiting equally

Explanation

Stoichiometry requires 2 mol H2 per 1 mol O2. 3.0 mol H2 needs only 1.5 mol O2, so O2 is in excess and H2 is limiting.

Question 9Physical chemistry, amounts and reactions

How many moles of H2O form when 3.0 mol H2 reacts completely with excess O2 (2 H2 + O2 -> 2 H2O)?

  1. 1.5 mol
  2. 3.0 mol Correct answer.
  3. 4.5 mol
  4. 6.0 mol

Explanation

With excess O2, H2 limits. The H2:H2O ratio is 1:1, so 3.0 mol H2 produces 3.0 mol H2O.

Question 10Physical chemistry, amounts and reactions

What mass of CO2 forms from complete combustion of 1.00 mol CH4? (M(CO2) = 44.0 g mol-1; CH4 + 2 O2 -> CO2 + 2 H2O)

  1. 16.0 g
  2. 32.0 g
  3. 44.0 g Correct answer.
  4. 88.0 g

Explanation

1.00 mol CH4 produces 1.00 mol CO2. m = nM = 1.00 x 44.0 = 44.0 g.

Question 11Physical chemistry, amounts and reactions

A 2.50 g sample of pure metal oxide MO contains 2.00 g of metal M. The molar mass of M is closest to (O = 16.0 g mol-1)

  1. 16 g mol-1
  2. 32 g mol-1
  3. 64 g mol-1 Correct answer.
  4. 80 g mol-1

Explanation

Oxygen mass = 0.50 g, so n(O) = 0.50/16.0 = 0.03125 mol. For MO, n(M) = n(O). M(M) = 2.00/0.03125 = 64 g mol-1.

Question 12Physical chemistry, amounts and reactions

How many molecules are in 0.50 mol of N2? (NA = 6.0 x 10^23 mol-1)

  1. 3.0 x 10^23 Correct answer.
  2. 6.0 x 10^23
  3. 1.2 x 10^24
  4. 1.5 x 10^23

Explanation

N = n x NA = 0.50 x 6.0 x 10^23 = 3.0 x 10^23 molecules.

Question 13Physical chemistry, amounts and reactions

In the half-reaction Fe2+ -> Fe3+ + e-, which species is oxidized?

  1. Fe3+
  2. Fe2+ Correct answer.
  3. The electron
  4. Water

Explanation

Oxidation is loss of electrons. Fe2+ loses one electron to become Fe3+, so Fe2+ is oxidized.

Question 14Physical chemistry, amounts and reactions

Equal volumes of 0.20 M AgNO3 and 0.20 M NaCl are mixed. What is the main solid product?

  1. NaNO3(s)
  2. AgCl(s) Correct answer.
  3. AgNO3(s)
  4. NaCl(s)

Explanation

Ag+ + Cl- -> AgCl(s) is a classic low-solubility precipitation. NaNO3 remains dissolved; the starting salts are soluble.

Question 15Physical chemistry, amounts and reactions

A gas sample has P = 1.0 atm, V = 10.0 L, T = 273 K. Using PV = nRT with R = 0.0821 L atm mol-1 K-1, n is closest to

  1. 0.22 mol
  2. 0.45 mol Correct answer.
  3. 1.0 mol
  4. 2.2 mol

Explanation

n = PV/RT = (1.0 x 10.0)/(0.0821 x 273) is about 10/22.4, which is about 0.45 mol.

Question 16Physical chemistry, amounts and reactions

What volume of 0.100 M NaOH is needed to neutralise 25.0 mL of 0.100 M HCl (1:1 stoichiometry)?

  1. 12.5 mL
  2. 25.0 mL Correct answer.
  3. 50.0 mL
  4. 100 mL

Explanation

n(HCl) = 0.100 mol L-1 x 0.0250 L = 0.00250 mol. For 1:1 neutralisation, V(NaOH) = 0.00250/0.100 = 0.0250 L = 25.0 mL.

Question 17Physical chemistry, amounts and reactions

A compound has empirical formula CH2 and molar mass 56 g mol-1. Its molecular formula is

  1. CH2
  2. C2H4
  3. C3H6
  4. C4H8 Correct answer.

Explanation

Empirical mass of CH2 is 14 g mol-1. 56/14 = 4, so the molecular formula is (CH2)4 = C4H8.

Question 18Physical chemistry, amounts and reactions

In a redox reaction, the oxidizing agent

  1. is oxidized and loses electrons
  2. is reduced and gains electrons Correct answer.
  3. always contains oxygen
  4. must be a metal ion

Explanation

The oxidizing agent causes oxidation of another species by accepting electrons; it is itself reduced.

Question 19Physical chemistry, amounts and reactions

What mass of NaOH is needed to prepare 250 mL of 0.400 M NaOH? (M = 40.0 g mol-1)

  1. 2.00 g
  2. 4.00 g Correct answer.
  3. 10.0 g
  4. 40.0 g

Explanation

n = cV = 0.400 mol L-1 x 0.250 L = 0.100 mol. m = nM = 0.100 x 40.0 = 4.00 g.

Question 20Physical chemistry, amounts and reactions

For N2 + 3 H2 -> 2 NH3, how many moles of H2 are required to produce 4.0 mol NH3 (complete conversion)?

  1. 2.0 mol
  2. 3.0 mol
  3. 6.0 mol Correct answer.
  4. 12 mol

Explanation

The H2:NH3 ratio is 3:2. For 4.0 mol NH3, n(H2) = 4.0 x (3/2) = 6.0 mol.

Question 21Physical chemistry, amounts and reactions

A 0.100 M strong monoprotic acid is diluted by a factor of 10 (volume multiplied by 10). The new pH is closest to

  1. 1.0
  2. 2.0 Correct answer.
  3. 3.0
  4. 7.0

Explanation

Initial [H+] = 0.100 M gives pH 1.0. After 10x dilution, [H+] = 0.0100 M gives pH 2.0 (water autodissociation negligible here).

Question 22Physical chemistry, amounts and reactions

When 2.0 mol of CaCO3 decomposes completely (CaCO3 -> CaO + CO2), the volume of CO2 at STP is about (22.4 L mol-1)

  1. 11.2 L
  2. 22.4 L
  3. 44.8 L Correct answer.
  4. 67.2 L

Explanation

1 mol CaCO3 produces 1 mol CO2, so 2.0 mol produces 2.0 mol CO2 and 2.0 x 22.4 = 44.8 L at STP.

Question 23Physical chemistry, amounts and reactions

A mixture contains 2.0 mol Fe2O3 and 6.0 mol CO for Fe2O3 + 3 CO -> 2 Fe + 3 CO2. Maximum moles of Fe produced are

  1. 2.0 mol
  2. 4.0 mol Correct answer.
  3. 6.0 mol
  4. 8.0 mol

Explanation

2.0 mol Fe2O3 requires exactly 6.0 mol CO (1:3). Fe2O3:Fe = 1:2, so 2.0 mol Fe2O3 yields 4.0 mol Fe.

Question 24Physical chemistry, amounts and reactions

A sample of pure H2SO4 (M = 98.1 g mol-1) has mass 4.90 g. How many moles of H+ are available for complete neutralisation if both protons react?

  1. 0.025 mol
  2. 0.050 mol
  3. 0.10 mol Correct answer.
  4. 0.20 mol

Explanation

n(H2SO4) = 4.90/98.1 is about 0.050 mol. Each H2SO4 can release 2 H+, so n(H+) is about 0.10 mol.

Question 25Physical chemistry, amounts and reactions

Combustion of a 0.28 g hydrocarbon sample yields 0.88 g CO2 and 0.36 g H2O. The empirical formula is (C = 12, H = 1, O = 16)

  1. CH
  2. CH2 Correct answer.
  3. CH3
  4. C2H5

Explanation

n(C) from CO2 = 0.88/44 = 0.020 mol. n(H) from H2O = 2 x (0.36/18) = 0.040 mol. C:H = 0.020:0.040 = 1:2, so empirical formula CH2. Mass check: 0.24 g C + 0.04 g H = 0.28 g.

Question 26Physical chemistry, amounts and reactions

25.0 mL of 0.200 M Ba(OH)2 is titrated with 0.100 M HCl. Volume of HCl needed for complete neutralisation is

  1. 25.0 mL
  2. 50.0 mL
  3. 100 mL Correct answer.
  4. 200 mL

Explanation

n(Ba(OH)2) = 0.200 x 0.0250 = 0.00500 mol, providing 0.0100 mol OH-. HCl is monoprotic, so n(HCl) needed = 0.0100 mol. V = 0.0100/0.100 = 0.100 L = 100 mL.

Question 27Structure, bonding and inorganic chemistry

Which subatomic particle has a relative charge of +1 and a relative mass of approximately 1 u?

  1. Electron
  2. Proton Correct answer.
  3. Neutron
  4. Photon

Explanation

A proton has charge +1 and mass about 1 u. Electrons have charge -1 and much smaller mass; neutrons are neutral with mass about 1 u; photons are massless energy quanta.

Question 28Structure, bonding and inorganic chemistry

An atom of carbon-12 has 6 protons. How many neutrons does it have?

  1. 6 Correct answer.
  2. 12
  3. 18
  4. 0

Explanation

Mass number A equals protons plus neutrons. For carbon-12, A = 12 and Z = 6, so neutrons = 12 - 6 = 6.

Question 29Structure, bonding and inorganic chemistry

Which element is in Group 17 (halogens) of the periodic table?

  1. Sodium
  2. Calcium
  3. Chlorine Correct answer.
  4. Argon

Explanation

Chlorine is a Group 17 halogen. Sodium is Group 1, calcium Group 2, and argon Group 18.

Question 30Structure, bonding and inorganic chemistry

Which type of bonding typically forms between a metal and a non-metal?

  1. Covalent bonding
  2. Ionic bonding Correct answer.
  3. Metallic bonding
  4. Hydrogen bonding

Explanation

Metals tend to lose electrons and non-metals gain them, forming ions held by electrostatic attraction (ionic bonding), for example NaCl.

Question 31Structure, bonding and inorganic chemistry

Across a period, atomic radius generally decreases from left to right mainly because

  1. electron shielding increases strongly across the period
  2. nuclear charge increases while electrons enter the same shell Correct answer.
  3. atoms gain more neutrons
  4. metallic character increases

Explanation

Effective nuclear charge rises as protons are added while the principal shell stays the same, pulling electrons closer and shrinking the radius.

Question 32Structure, bonding and inorganic chemistry

Which molecule is nonpolar overall despite containing polar bonds?

  1. H2O
  2. NH3
  3. CO2 Correct answer.
  4. HF

Explanation

CO2 is linear (O=C=O); equal and opposite C=O bond dipoles cancel, so the molecule is nonpolar. H2O and NH3 have net dipoles; HF is polar.

Question 33Structure, bonding and inorganic chemistry

According to VSEPR theory, what is the electron-domain geometry of methane (CH4)?

  1. Linear
  2. Trigonal planar
  3. Tetrahedral Correct answer.
  4. Octahedral

Explanation

Carbon in CH4 has four bonding pairs and no lone pairs, so four electron domains arrange tetrahedrally (about 109.5 degrees).

Question 34Structure, bonding and inorganic chemistry

Which intermolecular force is primarily responsible for the unusually high boiling point of water?

  1. London dispersion forces only
  2. Ionic bonding between H2O molecules
  3. Hydrogen bonding Correct answer.
  4. Metallic bonding

Explanation

Water molecules form extensive O-H...O hydrogen bonds, requiring more energy to separate and elevating the boiling point relative to H2S and related hydrides.

Question 35Structure, bonding and inorganic chemistry

What is the oxidation state of sulfur in the sulfate ion SO4 2-?

  1. +2
  2. +4
  3. +6 Correct answer.
  4. -2

Explanation

Let S = x and take oxygen as -2: x + 4(-2) = -2, so x - 8 = -2 and x = +6.

Question 36Structure, bonding and inorganic chemistry

Which description best matches a metallic solid?

  1. Discrete molecules held only by hydrogen bonds
  2. Cations in a lattice of delocalized valence electrons Correct answer.
  3. Ions held only by directional covalent bonds
  4. Neutral atoms with no mobile electrons

Explanation

Metals consist of positive metal ions surrounded by a mobile sea of delocalized valence electrons, which explains conductivity and malleability.

Question 37Structure, bonding and inorganic chemistry

Resonance structures of a molecule or ion

  1. are rapidly interconverting real isomers
  2. are limiting Lewis forms; the true structure is a hybrid Correct answer.
  3. must have different molecular formulas
  4. always include unpaired electrons

Explanation

Resonance forms are alternative Lewis depictions of electron delocalization. The actual species is a resonance hybrid, not an equilibrium of distinct isomers.

Question 38Structure, bonding and inorganic chemistry

Which compound is expected to have the highest lattice energy under similar packing assumptions?

  1. NaCl
  2. KBr
  3. MgO Correct answer.
  4. CsI

Explanation

Lattice energy rises with ion charge product and falls with ion size. Mg2+ and O2- give charge product 4 versus 1 for alkali halides, so MgO has much larger lattice energy.

Question 39Structure, bonding and inorganic chemistry

First ionization energy generally increases across a period. Which exception pattern is commonly observed?

  1. Noble gases always have the lowest first ionization energy
  2. Group 13 may have lower IE1 than Group 2 because the electron removed is a p electron Correct answer.
  3. Halogens always have lower IE1 than alkali metals
  4. Transition metals show no ionization-energy trends

Explanation

Beryllium (2s2) has higher IE1 than boron (2s2 2p1) because removing a 2p electron from B is easier than disrupting a filled 2s subshell in Be. Similar anomalies occur for N versus O.

Question 40Structure, bonding and inorganic chemistry

In the Lewis structure of NH4+, how many bonding pairs surround nitrogen and what is nitrogen's formal charge?

  1. 3 bonding pairs; formal charge 0
  2. 4 bonding pairs; formal charge +1 Correct answer.
  3. 4 bonding pairs; formal charge -1
  4. 5 bonding pairs; formal charge +1

Explanation

NH4+ has four N-H single bonds and no lone pair on nitrogen. Formal charge on N is 5 - 0 - 4 = +1 (valence electrons minus nonbonding electrons minus half of bonding electrons).

Question 41Structure, bonding and inorganic chemistry

Which hybridisation is typically assigned to each carbon atom in ethene (C2H4)?

  1. sp
  2. sp2 Correct answer.
  3. sp3
  4. sp3d

Explanation

Each carbon in ethene is bonded in three regions of electron density and is described as sp2 hybridised with trigonal planar geometry.

Question 42Structure, bonding and inorganic chemistry

Compared with Cl2, the F-F bond is weaker than a simple size-trend argument might suggest. The best explanation is that

  1. fluorine has lower electronegativity than chlorine
  2. lone-pair repulsion is severe on the short F-F bond Correct answer.
  3. fluorine atoms have no valence electrons
  4. Cl2 is ionic while F2 is covalent

Explanation

Both are covalent diatomics. The F-F bond is short, so strong lone-pair-lone-pair repulsion weakens the bond relative to naive periodic expectations.

Question 43Structure, bonding and inorganic chemistry

An element has successive ionization energies (kJ mol-1): 738, 1450, 7730, 10500. Which ion is most likely formed in ionic compounds?

  1. M+
  2. M2+ Correct answer.
  3. M3+
  4. M4+

Explanation

A large jump after the second ionization energy (1450 to 7730) shows the third electron comes from a core shell. The element readily forms M2+.

Question 44Structure, bonding and inorganic chemistry

What molecular shape does VSEPR predict for SF4?

  1. Tetrahedral
  2. See-saw Correct answer.
  3. Square planar
  4. Trigonal bipyramidal

Explanation

Sulfur in SF4 has five electron domains (four bonds + one lone pair). Electron geometry is trigonal bipyramidal; the lone pair occupies an equatorial site, giving a see-saw molecular shape.

Question 45Structure, bonding and inorganic chemistry

Which statement about bonding in ethene is correct?

  1. The C=C double bond consists of two pi bonds only
  2. The C=C double bond consists of one sigma and one pi bond Correct answer.
  3. All C-H bonds in ethene are pi bonds
  4. Ethene has no sigma bonds

Explanation

A double bond is one sigma bond (end-on overlap) plus one pi bond (sideways p-p overlap). Each C-H bond is a sigma bond.

Question 46Physical chemistry, amounts and reactions

In the equation q = m c DeltaT, what does c represent?

  1. Heat capacity of the entire sample only
  2. Specific heat capacity Correct answer.
  3. Temperature in kelvin only
  4. Enthalpy of formation

Explanation

In q = m c DeltaT, c is specific heat capacity (energy per unit mass per degree), such as about 4.18 J g-1 C-1 for liquid water.

Question 47Physical chemistry, amounts and reactions

How does a catalyst typically increase reaction rate?

  1. By increasing the equilibrium constant K
  2. By providing an alternative pathway with lower activation energy Correct answer.
  3. By making the reaction more exothermic
  4. By increasing the stoichiometric coefficients

Explanation

Catalysts lower activation energy via an alternative mechanism, increasing rate for both forward and reverse paths without changing DeltaH or K of the overall reaction.

Question 48Physical chemistry, amounts and reactions

For the equilibrium A(g) + B(g) <=> C(g), increasing pressure by decreasing volume tends to

  1. Shift left toward more moles of gas
  2. Shift right toward fewer moles of gas Correct answer.
  3. Always leave composition unchanged
  4. Destroy the equilibrium constant definition

Explanation

Le Chatelier: higher pressure favours the side with fewer gas moles. Left has 2 mol gas, right has 1, so the system shifts right.

Question 49Physical chemistry, amounts and reactions

Activation energy is best described as

  1. The net enthalpy change of a reaction
  2. The minimum energy barrier that reactant molecules must overcome to form products Correct answer.
  3. The temperature of the reaction mixture
  4. The equilibrium constant of the reaction

Explanation

Activation energy Ea is the energy barrier between reactants and the transition state. Rate depends strongly on Ea and temperature.

Question 50Physical chemistry, amounts and reactions

How much heat is absorbed when 100 g of water is heated from 20.0 C to 30.0 C? (c = 4.18 J g-1 C-1)

  1. 418 J
  2. 2090 J
  3. 4180 J Correct answer.
  4. 8360 J

Explanation

q = m c DeltaT = 100 g x 4.18 J g-1 C-1 x 10.0 C = 4180 J.