Free IB Chemistry Questions and Answers — Questions and Answers

Question 1: Which of the following quantum number sequences cannot exist for an electron?

n = 2, l = 1, ml = 2, s = -1⁄2 (Correct answer)
n = 4, l = 1, ml = 1, s = -1⁄2
n = 4, l = 3, ml = 2, s = 1⁄2
n = 3, l = 2, ml = -1, s = 1⁄2

Correct answer: n = 2, l = 1, ml = 2, s = -1⁄2

Quantum numbers follow specific rules: the azimuthal quantum number (l) must be less than the principal quantum number (n), and the magnetic quantum number (ml) must be an integer between -l and +l. In the sequence n=2, l=1, ml=2, the value of ml (2) exceeds the allowed range for l=1 (which is -1, 0, 1). Therefore, this set of quantum numbers is invalid and cannot exist for an electron.

Question 2: Which of the subsequent hybridizations would allow one pi bond to form?

sp
sp3
sp2 (Correct answer)
s2

Correct answer: sp2

An sp² hybridized atom involves the mixing of one s orbital and two p orbitals, resulting in three sp² hybrid orbitals that form sigma bonds. This leaves one unhybridized p orbital available. This unhybridized p orbital can then overlap sideways with a similar p orbital from an adjacent atom to form a single pi (π) bond, which is characteristic of double bonds.

Question 3: A cell submerged in purified water has enlarged. Why?

The cell was in a hypotonic environment, so water flowed into it. (Correct answer)
The cell was in an isotonic environment, so water flowed into it.
The cell was in a hypotonic environment, so water flowed out of it.
The cell was in a hypertonic environment, so water flowed into it.

Correct answer: The cell was in a hypotonic environment, so water flowed into it.

When a cell is placed in purified water, the external environment is hypotonic, meaning it has a lower solute concentration than the cell's cytoplasm. Due to osmosis, water molecules move from an area of higher water concentration (outside the cell) to an area of lower water concentration (inside the cell) across the semi-permeable membrane. This net influx of water causes the cell to swell and enlarge.

Question 4: H2S + H2O --> HS- + H3O+ What is the conjugate base of H2S in the aforementioned reaction?

H3O+
H2O
H2S has no conjugate base
HS (Correct answer)

Correct answer: HS

According to the Brønsted-Lowry acid-base theory, an acid is a proton (H⁺) donor, and its conjugate base is the species formed after the acid has donated its proton. In the reaction H₂S + H₂O → HS⁻ + H₃O⁺, H₂S acts as an acid by donating a proton to H₂O. When H₂S loses a proton, it forms HS⁻, which is therefore its conjugate base.

Question 5: What phrase describes a transition from a solid to a gas quickly?

Deposition
Sublimation (Correct answer)
Vaporization
Effervescence

Correct answer: Sublimation

Sublimation is a phase transition where a substance changes directly from a solid state to a gaseous state without passing through an intermediate liquid phase. This process occurs when the vapor pressure of the solid is sufficiently high, allowing molecules to escape directly into the gas phase.

Question 6: What is the most electronegative of the following elements?

Lithium
Oxygen (Correct answer)
Boron
Potassium

Correct answer: Oxygen

Electronegativity is a measure of an atom's ability to attract electrons in a chemical bond. It generally increases across a period and decreases down a group in the periodic table. Among the given elements, Oxygen is located in the upper right portion of the periodic table (Group 16, Period 2), making it significantly more electronegative than Lithium, Boron, or Potassium.

Question 7: At 25 degrees Celsius, which of the following elements is a liquid?

Chlorine
Boron
Mercury (Correct answer)
Silicon

Correct answer: Mercury

At 25 degrees Celsius, which is standard room temperature, mercury (Hg) is unique among the listed elements for being a liquid. Chlorine is a gas, while boron and silicon are solid metalloids. This property makes mercury distinctive and useful in applications like thermometers.

Question 8: Which of the following scenarios ensures that an unplanned, forward-moving reaction will take place?

Change in entropy is negative
Change in Gibbs free energy is negative (Correct answer)
Change in enthalpy is positive
The temperature is negative

Correct answer: Change in Gibbs free energy is negative

For a chemical reaction to be spontaneous (meaning it will proceed in the forward direction without external energy input) under constant temperature and pressure, the change in Gibbs free energy (ΔG) must be negative. A negative ΔG indicates that the reaction releases free energy, making it thermodynamically favorable.

Question 9: In order to induce a non-spontaneous reaction to occur, electrolysis needs energy input. False or true?

False
True (Correct answer)

Correct answer: True

Electrolysis is a process that uses electrical energy to drive non-spontaneous chemical reactions. These reactions, by definition, have a positive change in Gibbs free energy and would not occur on their own. Therefore, an external input of energy, typically in the form of an electric current, is required to force the reaction to proceed.

Question 10: Which of the following elements has an atomic radius that is the largest?

Fluorine
Potassium
Rubidium (Correct answer)
Boron

Correct answer: Rubidium

Atomic radius generally increases as you move down a group in the periodic table due to the addition of electron shells, and it decreases across a period from left to right due to increased nuclear charge. Rubidium (Rb) is in Group 1, Period 5, placing it lower and further left than Fluorine (Group 17, Period 2), Potassium (Group 1, Period 4), and Boron (Group 13, Period 2), thus giving it the largest atomic radius among the options.

Question 11: 3.0 moles of H20 are used to dissolve 80.0 grams of NaOH. What percentage of NaOH by moles is present in this solution?

.30
.40 (Correct answer)
.64
.35

Correct answer: .40

First, calculate the moles of NaOH: 80.0 g / 40.00 g/mol (molar mass of NaOH) = 2.0 moles NaOH. The total moles in the solution are 2.0 moles NaOH + 3.0 moles H₂O = 5.0 moles. The mole percentage of NaOH is then (2.0 moles NaOH / 5.0 total moles) = 0.40.

Free IB Chemistry Questions and Answers

Which of the following quantum number sequences cannot exist for an electron?