Structure: Models of the Particulate Nature of Matter — Free Chemistry SL Practice Questions

The graph below shows the heating curve of a pure substance. Temperature is plotted against time as the substance is heated from $-50\,°\text{C}$ to $150\,°\text{C}$ at a constant rate. The substance has a melting point of $0\,°\text{C}$ and a boiling point of $100\,°\text{C}$. The specific heat capacity of the solid is $2.1\,\text{J}\,\text{g}^{-1}\,°\text{C}^{-1}$ and of the liquid is $4.2\,\text{J}\,\text{g}^{-1}\,°\text{C}^{-1}$.

The phase for carbon dioxide ($\text{CO}_2$) is shown below (not to scale). The triple point of $\text{CO}_2$ is at $5.11\,\text{atm}$ and $-56.6\,°\text{C}$. The critical point is at $73.0\,\text{atm}$ and $31.1\,°\text{C}$. At $1\,\text{atm}$ pressure, solid $\text{CO}_2$ sublimes at $-78.5\,°\text{C}$.

A class investigates the cooling of a pure substance X. Liquid X at $120\,^\circ\text{C}$ is cooled to $20\,^\circ\text{C}$ at a constant rate of heat removal. Property — Value Normal boiling point of X — $78.5\,^\circ\text{C}$ Normal melting point of X — $-114.5\,^\circ\text{C}$ Specific heat capacity of liquid X — $2.50\,\text{J g}^{-1}\,^\circ\text{C}^{-1}$ Specific heat capacity of solid X — $2.00\,\text{J g}^{-1}\,^\circ\text{C}^{-1}$ Enthalpy of vaporisation of X — $840\,\text{J g}^{-1}$ Enthalpy of fusion of X — $180\,\text{J g}^{-1}$ Mass of sample — $50.0\,\text{g}$ Rate of heat removal — $20.0\,\text{J s}^{-1}$

A student investigates the behaviour of a pure sample of water as it is heated from $-10\,°\text{C}$ to $120\,°\text{C}$ at constant atmospheric pressure. The student records the temperature every 30 seconds and plots a heating curve. The specific latent heat of vaporization of water is $2.26 \times 10^{3}\,\text{J g}^{-1}$.

A student places a few crystals of solid iodine ($\text{I}_2$) in a sealed flask at $25\,^\circ\text{C}$ and standard atmospheric pressure ($101\,\text{kPa}$). Over time, the solid disappears and a purple vapour fills the flask, with no liquid observed. The triple point of iodine occurs at $113.7\,^\circ\text{C}$ and $12.1\,\text{kPa}$.

Bohr's model of the hydrogen atom describes electrons occupying discrete energy levels. A hydrogen atom in its ground state absorbs a photon and undergoes electronic excitation.

A student studies the mass spectrum of a pure sample of magnesium. Magnesium has three naturally occurring isotopes: $^{24}$Mg, $^{25}$Mg, and $^{26}$Mg.

This question is about the hydrogen atomic spectrum and atomic models. The hydrogen emission spectrum shows a series of lines in the visible region (Balmer series), corresponding to electronic transitions from higher energy levels to $n = 2$.

A lithium-7 atom has the electron configuration $1s^2\,2s^1$. Its nucleus contains 3 protons and 4 neutrons.

Rutherford's gold foil experiment provided evidence for the nuclear model of the atom. Alpha particles were directed at a thin gold foil.

The emission spectrum of atomic hydrogen contains a series of lines in the ultraviolet region known as the Lyman series. These lines correspond to electron transitions from higher energy levels ($n > 1$) to the ground state ($n = 1$).

Nitrogen (N, $Z = 7$) is a key component of amino acids and fertilisers. A student writes the following electron configuration for a nitrogen atom in its ground state: $$1s^2 \ 2p_x^1 \ 2p_y^1$$ -

Technetium (Tc, $Z = 43$) is the lightest element with no stable isotopes. It is used in nuclear medicine as a gamma-emitting tracer. Its neighbour molybdenum (Mo, $Z = 42$) has anomalous ground-state electron configuration compared to the prediction of the Aufbau principle.

A student performs flame emission spectroscopy on a sample containing strontium ions ($\text{Sr}^{2+}$). The strontium spectrum shows two closely spaced red emission lines at wavelengths $\lambda_1 = 460.7\,\text{nm}$ and $\lambda_2 = 460.3\,\text{nm}$.

A student proposes the following electron configuration for a sulfur atom ($Z = 16$) in its ground state: $$1s^2\; 2p^6\; 3s^2\; 3p_x^{\uparrow\downarrow}\; 3p_y^{\uparrow}\; 3p_z^{\phantom{\uparrow}}$$ where $3p_y$ is shown with two electrons of parallel (same) spin.

A student investigates the composition of hydrated magnesium sulfate, $\text{MgSO}_4 \cdot n\text{H}_2\text{O}$. The student places a clean, dry crucible on a balance and records a mass of $18.24\,\text{g}$. A sample of the hydrated salt is added and the new mass recorded as $28.76\,\text{g}$. The crucible and contents are heated strongly for several minutes to drive off all water of crystallisation, then cooled in a desiccator. The final mass of the crucible and anhydrous salt is $23.54\,\text{g}$. $$M(\text{MgSO}_4) = 120.4\,\text{g\,mol}^{-1} \qquad M(\text{H}_2\text{O}) = 18.02\,\text{g\,mol}^{-1}$$

A student investigates the behaviour of dinitrogen monoxide, $\text{N}_2\text{O}$, used as a mild anaesthetic in dentistry. A sealed syringe contains $0.920\,\text{g}$ of $\text{N}_2\text{O}$ at $22.0\,°\text{C}$ and occupies a volume of $0.500\,\text{dm}^3$.

A student investigates Charles's law using a capillary tube sealed at one end. A small plug of concentrated sulfuric acid traps a fixed mass of dry air. The tube is heated in a water bath and the length of the air column is measured at different temperatures. - Length of air column at $30.0\,°\text{C}$: $8.20\,\text{cm}$ - Length of air column at $80.0\,°\text{C}$: $9.55\,\text{cm}$

A student investigates thermal decomposition of calcium carbonate ($\text{CaCO}_3$) in a sealed, rigid container of volume $5.00 \times 10^{-3}\,\text{m}^3$. The container is initially evacuated, a sample of pure $\text{CaCO}_3$ is placed inside, and the container is sealed. The container is heated to a constant temperature of $1100\,\text{K}$, at which the reaction $$\text{CaCO}_3(s) \rightarrow \text{CaO}(s) + \text{CO}_2(g)$$ goes to completion. The pressure of $\text{CO}_2(g)$ in the container is then measured to be $1.83 \times 10^5\,\text{Pa}$.

A weather balloon is filled with helium gas at sea level where the atmospheric pressure is $1.01 \times 10^{5}\,\text{Pa}$ and the temperature is $298\,\text{K}$. The balloon has a volume of $2.50 \times 10^{3}\,\text{m}^{3}$ when fully inflated at sea level. As the balloon rises, the external pressure decreases and the temperature drops. At an altitude of $15\,\text{km}$, the pressure is $1.20 \times 10^{4}\,\text{Pa}$ and the temperature is $217\,\text{K}$. The balloon is flexible and its volume adjusts to match external pressure. $$R = 8.31\,\text{J K}^{-1}\text{mol}^{-1} \qquad M(\text{He}) = 4.00\,\text{g mol}^{-1}$$

A researcher studies the behaviour of ammonia gas ($\text{NH}_3$) in a refrigeration cycle. She measures the pressure of a fixed amount of $\text{NH}_3$ as she compresses it at constant temperature, plotting pressure ($P$) against volume ($V$).