Electrochemistry and Atomic Structure Lecture Notes

Comprehensive practice flashcards covering Chapter 10 (Electrochemistry: redox definitions, oxidation numbers, electrochemical cells, SHE, lead-acid batteries, and Faraday's laws) and Chapter 2 (Atomic Structure: cathode rays, Planck's quantum theory, Bohr's atomic model, hydrogen spectral series, orbits vs orbitals, and quantum numbers).

What is electrochemistry?

The branch of chemistry that deals with the relationship between electricity and chemical reactions, specifically the interconversion of electrical energy and chemical energy.

How do electrolytic cells differ from voltaic cells in terms of energy conversion?

Electrolytic cells convert electrical energy into chemical energy to drive non-spontaneous reactions, whereas voltaic cells convert chemical energy into electrical energy through spontaneous redox reactions.

What are the four definitions of oxidation given in the notes?

1. Addition of oxygen
2. Removal of hydrogen
3. Loss of electrons
4. Increase in oxidation number

What are the four definitions of reduction given in the notes?

1. Removal of oxygen
2. Addition of hydrogen
3. Gain of electrons
4. Decrease in oxidation number

What is an oxidation number (or oxidation state)?

The apparent charge assigned to an atom of an element in a molecule or in an ion.

What is the oxidation number of nitrogen in $HNO_3$?

$$+5$$

What is the oxidation number of sulfur in $H_2SO_4$?

$$+6$$

What is the oxidation number of chlorine in $Ca(ClO_3)_2$?

$$+5$$

What is the oxidation number of manganese in $K_2MnO_4$?

$$+6$$

What is a disproportionation reaction?

A type of redox reaction where a single chemical species is both oxidized and reduced simultaneously, resulting in two or more different products containing the same element.

What is standard electrode potential (single electrode potential)?

The potential difference set up between an electrode (metal) and its ions in an electrolyte (solution) under equilibrium conditions.

What are the components and conditions of the Standard Hydrogen Electrode (SHE)?

It consists of a platinum foil coated electrolytically with finely divided platinum black suspended in a $1\,M$ $HCl$ solution, into which pure hydrogen gas at $1\,\text{atm}$ is continuously bubbled. Its potential is arbitrarily taken as $0\,\text{V}$.

What is cell potential ($E^\circ_{\text{cell}}$ or EMF)?

The force with which electrons are pushed to flow through the wire from the anode to the cathode, measuring the potential difference between two half-cells in an electrochemical cell.

What are the anode, cathode, and electrolyte in a lead storage battery?

Anode: Lead plate ($Pb$); Cathode: Lead dioxide ($PbO_2$); Electrolyte: $30\%$ $H_2SO_4$ solution with a density of $1.25\,\text{g\,cm}^{-3}$.

What is the overall chemical reaction during the discharge of a lead storage battery?

$$Pb + PbO_2 + 2H_2SO_4 \rightarrow 2PbSO_4 + 2H_2O$$

What is Faraday's first law of electrolysis?

The mass of a substance liberated or deposited on an electrode is directly proportional to the total quantity of electric charge passing through the electrolyte ($m = zQ = zIt$).

What is Faraday's second law of electrolysis?

When the same quantity of electricity is passed through different electrolytes, the masses of substances liberated or deposited at the electrodes are proportional to their equivalent (chemical) weights.

What occurs in a gas discharge tube as pressure is decreased from $1\,\text{atm}$ to $0.01\,\text{torr}$?

At $1\,\text{atm}$, gases do not conduct electricity. When pressure is reduced at high voltage ($5000\text{ to }10000\,\text{V}$), a uniform glow appears. At $0.01\,\text{torr}$, the glow disappears and cathode rays are emitted.

What is the charge-to-mass ($e/m$) ratio of an electron?

$$1.758820 \times 10^{11}\,\text{C\,kg}^{-1}$$

According to Planck's quantum theory, how is energy emitted or absorbed by a body?

Energy is not emitted or absorbed continuously, but discontinuously in the form of discrete wave packets called quanta, where $E = h\nu$.

What is Bohr's postulate regarding the angular momentum of a revolving electron?

The angular momentum ($mvr$) of an electron is an integral multiple of $\frac{h}{2\pi}$, given by $mvr = \frac{nh}{2\pi}$ where $n = 1, 2, 3, 4\dots$.

What is the radius of the first orbit ($n = 1$) of a hydrogen atom according to Bohr's model?

$$0.529\,\text{Å}$$

What is the formula for the energy of an electron in the $n^{\text{th}}$ shell of a hydrogen-like atom?

$E_n = -\frac{2.178 \times 10^{-18} \times Z^2}{n^2}\,\text{J}$ or $E_n = -\frac{1313.315 \times Z^2}{n^2}\,\text{kJ\,mol}^{-1}$

Which spectral regions correspond to the Lyman, Balmer, and Paschen series in the hydrogen spectrum?

Lyman series ($n_1 = 1$): Ultraviolet (UV); Balmer series ($n_1 = 2$): Visible; Paschen series ($n_1 = 3$): Infrared (IR).

What are the Zeeman and Stark effects that Bohr's model failed to explain?

The Zeeman effect is the splitting of spectral lines in the presence of a magnetic field; the Stark effect is the splitting of spectral lines in the presence of an electric field.

How does an orbit differ from an orbital?

An orbit is a circular path around the nucleus denoted by $K, L, M, N$, while an orbital is a three-dimensional region of space where the probability of finding an electron is highest ($s, p, d, f$).

What are the geometric shapes and maximum electron capacities of $s$, $p$, and $d$ orbitals?

$s$ orbital: spherical ($2$ electrons); $p$ orbital: dumb-bell shaped with $3$ orientations ($6$ electrons); $d$ orbital: clover leaf shaped with $5$ orientations ($10$ electrons).

What property of an electron is described by each of the four quantum numbers?

1. Principal quantum number ($n$): main energy level (orbit) and size
2. Azimuthal quantum number ($l$): sub-energy level (orbital shape)
3. Magnetic quantum number ($m$): spatial orientation of an orbital
4. Spin quantum number ($s$): spin movement of the electron

What does the Aufbau principle state regarding electron configuration?

Electrons fill atomic orbitals in order of increasing energy, following the order: $1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p$.