FREE IB Chemistry Questions and Answers

Question 1

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

Accepted Answer

n = 2, l = 1, ml = 2, s = ^-1⁄₂

Answer

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?

Accepted Answer

sp<sup>2</sup>

Answer

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?

Accepted Answer

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

Answer

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?

Accepted Answer

HS

Answer

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?

Accepted Answer

Sublimation

Answer

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.

IB - International Baccalaureate Practice Test

IB - International Baccalaureate Practice Test

FREE IB Chemistry Questions and Answers