IB Chemistry HL Structure 1: Models of the particulate nature of matter questions

Answer: C. For the same gas, average kinetic energy per particle is proportional to temperature in kelvin. Converting gives 293.15 K and 313.15 K, so the ratio is 313.15/293.15 = 1.07.

A: calculates the fractional increase, 20/293.15 ≈ 0.07, rather than the final ratio.
B: reverses the ratio, using 293.15/313.15 ≈ 0.94.
D: uses the Celsius readings directly, giving 40.0/20.0 = 2.00.

Remember: use kelvin values when forming a ratio of temperatures.

Answer: A. For a nuclide, the proton number is $Z$ and the neutron number is $A-Z$ a $2+$ charge means two fewer electrons than protons. Thus $p=29$ $n=65-29=36$ and $e=29-2=27$

B: adds 2 to the proton number when finding electrons, reversing the charge effect.
C: uses the electron count instead of the proton number in $A-Z$ giving 38 neutrons.
D: assumes the ion has the same number of electrons as a neutral copper atom, ignoring its charge.

Remember: ion formation changes the number of electrons, not the nucleus.

Answer: A. The highest-energy convergence limit corresponds to transitions ending at the lowest energy level, $n=1$ Its maximum capacity is $2n^2=2(1)^2=2$ electrons.
B: assigns the limit to $n=2$ then correctly applies $2n^2$
C: assigns the limit to $n=3$ then correctly applies $2n^2$
D: identifies $n=1$ but omits the factor of 2 in the capacity relation.
Remember: the maximum number of electrons in level $n$ is $2n^2$

Answer: D. For equal sample masses, particle number is inversely proportional to relative particle mass. Mr(C₆H₁₂O₆) = 6(12.01) + 12(1.01) + 6(16.00) = 180.18 (no units), which is greater than Ar(Fe) = 55.85; therefore, the iron sample has more particles. Each glucose molecule contains 24 atoms, so total atom numbers are proportional to 24/180.18 for glucose and 1/55.85 for iron. The glucose sample has more atoms overall.

A: treats relative mass as directly proportional to particle number; its conclusion about total atoms is correct.
B: gets the particle comparison right but overlooks the 24 atoms in each glucose molecule.
C: uses direct proportionality for particle number and fails to account for the 24 atoms per glucose molecule when comparing total atoms.
Remember: equal masses contain more particles of the substance with the lower relative particle mass, but total atom counts also depend on atoms per particle.

Answer: D. For a fixed amount of gas, $P \propto T/V$ Thus, $P_2=P_1(V_1/V_2)(T_2/T_1)=(8.0\times10^4)(2.0)(1.5)=2.4\times10^5\ \mathrm{Pa}$

A: reverses the temperature ratio, using $T_1/T_2$ instead of $T_2/T_1$
B: accounts for the temperature increase but omits the volume decrease.
C: accounts for the volume decrease but omits the temperature increase.
Remember: at fixed amount, pressure increases with temperature and decreases with volume.