Allied Health Sciences Entry Test Chemistry Syllabus

What is solvent extraction and the principle behind it?

Solvent extraction separates a solute from one solvent using another immiscible solvent in which the solute is more soluble. It is based on the distribution (partition) of a solute between two immiscible liquids.

State the distribution (partition) law.

At constant temperature, a solute distributes itself between two immiscible solvents so that the ratio of its concentrations in the two solvents is constant: C1/C2 = Kd (distribution coefficient).

What is chromatography and what is it used for?

Chromatography is a technique to separate, identify, and purify components of a mixture based on their different distribution between a stationary phase and a mobile phase.

Name the stationary and mobile phases in paper chromatography.

Stationary phase: water held on the cellulose (filter paper). Mobile phase: the solvent (liquid) that moves up the paper.

Define the Rf value in chromatography and give its formula.

Rf (retention factor) = distance travelled by the solute / distance travelled by the solvent front. It is constant for a substance under fixed conditions and always less than 1.

State Boyle's law and its mathematical expression.

At constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure: P x V = constant, or P1V1 = P2V2.

State Charles's law and its mathematical expression.

At constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute (Kelvin) temperature: V/T = constant, or V1/T1 = V2/T2.

State Avogadro's law.

Equal volumes of all gases at the same temperature and pressure contain an equal number of molecules. Volume is directly proportional to the number of moles (V proportional to n).

State Dalton's law of partial pressures.

The total pressure of a mixture of non-reacting gases equals the sum of the partial pressures of the individual gases: P_total = P1 + P2 + P3 + ...

State Graham's law of diffusion.

At constant temperature and pressure, the rate of diffusion of a gas is inversely proportional to the square root of its density (or molar mass): rate proportional to 1/sqrt(M).

Write the ideal gas equation and identify each term.

PV = nRT, where P = pressure, V = volume, n = number of moles, R = universal gas constant, T = absolute temperature (Kelvin).

Give the value of the gas constant R in SI units and in dm^3 atm units.

R = 8.314 J mol^-1 K^-1 (SI), or 0.0821 dm^3 atm mol^-1 K^-1.

How can molar mass be determined using the ideal gas equation?

Since n = mass/M, substituting gives PV = (m/M)RT, so M = mRT/(PV). Knowing mass, P, V, and T allows molar mass calculation.

State the main postulates of the kinetic molecular theory of gases.

Gases consist of tiny particles in constant random motion; their volume is negligible compared to container volume; collisions are perfectly elastic; there are no intermolecular forces; and average kinetic energy is directly proportional to absolute temperature.

According to kinetic molecular theory, what is average kinetic energy proportional to?

The average kinetic energy of gas molecules is directly proportional to the absolute (Kelvin) temperature.

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

At high pressure and low temperature, because molecules are close together so intermolecular forces and the finite molecular volume become significant.

Why does the ideal gas equation fail for real gases?

It assumes molecules have negligible volume and no intermolecular forces. Real molecules occupy space and attract one another, so these assumptions break down, especially at high pressure and low temperature.

Write the van der Waals equation for real gases.

(P + an^2/V^2)(V - nb) = nRT, where 'a' corrects for intermolecular attraction and 'b' corrects for the finite volume of molecules.

What is the compressibility factor Z, and what does its value indicate?

Z = PV/nRT. For an ideal gas Z = 1; Z greater than 1 indicates dominance of repulsive forces/molecular volume, and Z less than 1 indicates dominance of attractive forces.

List the main types of intermolecular forces in order of increasing strength.

London dispersion forces (weakest) < dipole-dipole forces < hydrogen bonding (strongest of the intermolecular forces).

What are London dispersion forces and in which molecules do they occur?

Weak attractions arising from temporary (instantaneous) dipoles caused by fluctuating electron clouds. They occur in all molecules but are the only force in nonpolar molecules; they increase with molecular size/polarizability.

What conditions are required for hydrogen bonding?

Hydrogen must be bonded to a highly electronegative atom (F, O, or N), and a lone pair must be present on the electronegative atom of a neighbouring molecule.

Why does water have an unusually high boiling point compared to H2S?

Water molecules form strong intermolecular hydrogen bonds (O-H...O), requiring much more energy to separate, whereas H2S has only weak dipole-dipole and dispersion forces.

Define surface tension and explain why it occurs.

Surface tension is the force acting along the surface of a liquid that tends to minimize its surface area. It arises because surface molecules experience a net inward pull from unbalanced intermolecular attractions.

Define vapour pressure of a liquid and state how it changes with temperature.

Vapour pressure is the pressure exerted by the vapour in equilibrium with its liquid at a given temperature. It increases as temperature increases.

Define the boiling point of a liquid in terms of vapour pressure.

The boiling point is the temperature at which the vapour pressure of the liquid becomes equal to the external (atmospheric) pressure.

How does viscosity of a liquid change with temperature, and why?

Viscosity decreases as temperature increases, because higher kinetic energy overcomes intermolecular attractions, allowing molecules to flow past each other more easily.

Compare the four main types of crystalline solids by their constituent particles and bonding.

Ionic (ions, electrostatic bonds), Covalent/network (atoms, covalent bonds), Molecular (molecules, intermolecular forces), Metallic (positive ions in a sea of delocalized electrons, metallic bonds).

Distinguish between crystalline and amorphous solids.

Crystalline solids have a regular, repeating long-range ordered arrangement of particles and sharp melting points; amorphous solids lack long-range order and soften over a range of temperatures (e.g., glass, rubber).

What is a unit cell in a crystal lattice?

A unit cell is the smallest repeating structural unit of a crystal lattice that, when repeated in three dimensions, generates the entire crystal.

Why do ionic solids have high melting points but are brittle?

High melting points result from strong electrostatic forces between oppositely charged ions; they are brittle because displacing the lattice brings like charges adjacent, causing repulsion that shatters the crystal.

State the relative charge and mass of the three subatomic particles.

Proton: charge +1, mass approx 1 amu. Neutron: charge 0, mass approx 1 amu. Electron: charge -1, mass approx 1/1836 amu (negligible).

Define atomic number and mass number.

Atomic number (Z) = number of protons in the nucleus. Mass number (A) = total number of protons plus neutrons in the nucleus.

What are isotopes?

Isotopes are atoms of the same element having the same atomic number (protons) but different mass numbers due to different numbers of neutrons.

State the two main postulates of Bohr's atomic model.

1) Electrons revolve around the nucleus only in fixed circular orbits (stationary states) of definite energy without radiating energy. 2) Energy is absorbed or emitted only when an electron jumps between orbits, equal to the energy difference (E = hf).

According to Bohr, how is the angular momentum of an electron quantized?

Angular momentum is quantized as mvr = n(h/2pi), where n is a whole number (1, 2, 3...), h is Planck's constant, and r is the orbit radius.

What is emitted when an electron falls from a higher to a lower energy level in Bohr's model?

A photon (quantum) of radiation is emitted with energy equal to the difference between the two levels: E = E_high - E_low = hf.

List the four quantum numbers and what each describes.

Principal (n): energy level/shell size. Azimuthal/subsidiary (l): subshell shape. Magnetic (m): orbital orientation in space. Spin (s): direction of electron spin (+1/2 or -1/2).

What are the allowed values of the azimuthal quantum number l, and which subshells do they represent?

l ranges from 0 to (n-1). l = 0 (s), 1 (p), 2 (d), 3 (f).

What are the possible values of the magnetic quantum number for a given l?

The magnetic quantum number m takes integer values from -l to +l, including 0, giving (2l + 1) orbitals in that subshell.

How many orbitals and maximum electrons are in s, p, d, and f subshells?

s: 1 orbital, 2 electrons. p: 3 orbitals, 6 electrons. d: 5 orbitals, 10 electrons. f: 7 orbitals, 14 electrons.

State the Aufbau principle.

Electrons fill orbitals in order of increasing energy, occupying the lowest-energy available orbital first before filling higher-energy ones.

State Pauli's exclusion principle.

No two electrons in an atom can have the same set of all four quantum numbers; an orbital holds at most two electrons, which must have opposite spins.

State Hund's rule of maximum multiplicity.

Electrons occupy degenerate (equal-energy) orbitals singly with parallel spins first, before any orbital is doubly occupied (pairing begins only after each orbital has one electron).

Write the (n+l) rule for determining orbital filling order.

Orbitals fill in order of increasing (n+l) value; if two orbitals have the same (n+l), the one with the lower n fills first. (e.g., 4s, with n+l=4, fills before 3d, with n+l=5).

Write the ground-state electronic configuration of chromium (Z=24) and explain the anomaly.

[Ar] 3d^5 4s^1 (not 3d^4 4s^2). A half-filled 3d^5 with 4s^1 gives extra stability due to symmetry and exchange energy.