Electrochemistry Practice Problems

  1. An atom with the electron configuration 1s22s22p63s23p63d54s2 has an incomplete…
  1. 2p sublevel
  2. Second principal energy level
  3. Third principal energy level
  4. 4s sublevel
Show Answer
The correct answer is C!

The configuration is 1s22s22p63s23p63d54s2.

  1. \(n = 1\) has 2 electrons (full)
  2. \(n = 2\) has 8 electrons (full)
  3. \(n = 3\) can hold up to 18 electrons (3s, 3p, 3d)

Here, it has 13, so the third principal energy level is incomplete.

 

  1. What is the total number of electrons in a completely filled fourth principal level?
  1. 8
  2. 10
  3. 16
  4. 32
Show Answer
The correct answer is D!

A completely filled level \(n\) contains \(2n^2\) electrons.

For \(n = 4\):

\(2(4^2) = 2 \times 16 = 32\)

So a full fourth principal level has 32 electrons.

 

  1. When is the characteristic bright line spectrum of an element produced?
  1. Its electrons form a covalent bond.
  2. Its electrons form an ionic bond.
  3. Its electrons move to a higher energy state.
  4. Its electrons move to a lower energy state.
Show Answer
The correct answer is D!

A bright-line emission spectrum occurs when electrons drop to lower energy levels, releasing photons with specific energies (wavelengths). Excitation absorbs energy, while emission releases it.

 

  1. Which emanation has no mass and no charge?
  1. α
  2. β
  3. γ
  4. n0
Show Answer
The correct answer is C!

  • α: mass ≈ 4 amu, charge +2
  • β: tiny mass, charge −1 or +1
  • γ: mass 0, charge 0
  • n0: mass ≈ 1 amu, charge 0

Only γ has no mass and no charge.

 

  1. In which system do molecule-ion attractions exist?
  1. NaCl(aq)
  2. NaCl(s)
  3. C6H12O6(aq)
  4. C6H12O6(s)
Show Answer
The correct answer is A!

Molecule–ion attractions occur when ions in solution attract polar molecules. NaCl(aq) features Na+/Cl–H2O (dipole) interactions (ion–dipole).

 

  1. What can a particle accelerator increase the kinetic energy of?
  1. An α-particle and a β-particle
  2. An α-particle and a neutron
  3. A γ-ray and a β-particle
  4. A neutron and a γ-ray
Show Answer
The correct answer is A!

Particle accelerators use electric fields to accelerate charged particles.

α (charge +2) and β (charge −1) can be accelerated. Neutrons (no charge) and γ-rays (photons) are not accelerated.

 

  1. What is the total number of electrons needed to completely fill all of the orbitals in an atom’s second principal energy level?
  1. 16
  2. 2
  3. 8
  4. 4
Show Answer
The correct answer is C!

The second principal level has sublevels 2s (1 orbital) and 2p (3 orbitals).

The total number of orbitals is 4, and each holds 2 electrons. This means that it takes 8 electrons to fill all orbitals.

 

  1. An atom in an excited state can have an electron configuration of…
  1. 1s22s2
  2. 1s22p1
  3. 1s22s22p2
  4. 1s22s22p5
Show Answer
The correct answer is B!

An excited-state configuration places one or more electrons in a higher-energy sublevel than in the ground state.

1s22p1 is excited for Li (ground state: 1s22s1).

The other options are ground-state configurations, so B is the only excited-state choice.

 

  1. Compared to the charge and mass of a proton, an electron has…
  1. The same charge and smaller mass
  2. The same charge and the same mass
  3. The opposite charge and smaller mass
  4. The opposite charge and the same mass
Show Answer
The correct answer is C!

A proton and an electron have opposite charges (+1 vs −1). The electron’s mass is about \(\tfrac{1}{1,836}\) of a proton’s, so it has a smaller mass.

 

  1. What is the total number of sublevels in the fourth principal energy level?
  1. 1
  2. 2
  3. 3
  4. 4
Show Answer
The correct answer is D!

The number of sublevels in principal level \(n\) equals \(n\).

For \(n = 4\), the sublevels are 4s, 4p, 4d, 4f (4 sublevels total).

 

  1. Which atom in the ground state has only one unpaired electron in its valence shell?
  1. Aluminum
  2. Silicon
  3. Phosphorus
  4. Sulfur
Show Answer
The correct answer is A!

  • Aluminum: 3s23p1 → one unpaired (p1)
  • Silicon: 3s23p2 → two unpaired (Hund’s rule)
  • Phosphorus: 3s23p3 → three unpaired
  • Sulfur: 3s23p4 → two unpaired (one pair + two singles)

So aluminum has exactly one unpaired valence electron.

 

  1. Which of the following best describes the shape and bonding of a diatomic bromine molecule?
  1. Symmetrical and polar
  2. Symmetrical and nonpolar
  3. Asymmetrical and polar
  4. Asymmetrical and nonpolar
Show Answer
The correct answer is B!

Br2 is a diatomic molecule of identical atoms. The bond is nonpolar covalent, the molecule is linear and symmetrical, so overall it is nonpolar.

 

  1. What is the oxidation number of sulfur in H2SO4?
  1. 0
  2. -2
  3. +6
  4. +4
Show Answer
The correct answer is C!

Let oxidation states sum to 0 in H2SO4.

\(H = +1\)

\(O = −2\)

Let \(S = x\):

\(x + 2 + (-8)\) \(= 0 \Rightarrow x – 6 = 0 \Rightarrow x\) \(= +6\)

Therefore, sulfur is +6.

 

  1. When α-particles are used to bombard gold foil, most of the α-particles pass through undeflected. This result indicates that most of the volume of a gold atom consists of what?
  1. Neutrons
  2. Protons
  3. Deuterons
  4. Unoccupied space
Show Answer
The correct answer is D!

Rutherford’s gold-foil experiment showed most α-particles passed through undeflected, indicating the atom is mostly empty (unoccupied) space with a small, dense, positively charged nucleus.

 

  1. When an α-particle is emitted by an atom, what happens to the atomic number of the atom?
  1. It decreases by 2
  2. It increases by 2
  3. It decreases by 4
  4. It increases by 4
Show Answer
The correct answer is A!

An α-particle is a 42He nucleus. Emitting, it reduces the mass number by 4 and the atomic number by 2.

 

  1. Which of the following elements has the corresponding valence subshell of 3p4?
  1. Aluminum
  2. Silicon
  3. Sulfur
  4. Chlorine
Show Answer
The correct answer is C!

Valence 3p4 corresponds to sulfur.

 

  1. Which of the following elements has the corresponding valence subshell of 3p6?
  1. Sulfur
  2. Chlorine
  3. Argon
  4. Potassium
Show Answer
The correct answer is C!

Valence 3p6 is a closed p subshell → argon (noble gas).

 

  1. Which of the following elements has the corresponding valence subshell of 3s1?
  1. Neon
  2. Sodium
  3. Magnesium
  4. Aluminum
Show Answer
The correct answer is B!

Valence 3s1 is sodium (Na).

 

  1. Which of the following elements has the corresponding valence subshell of 2p4?
  1. Nitrogen
  2. Oxygen
  3. Neon
  4. Magnesium
Show Answer
The correct answer is B!

Valence 2p4 corresponds to oxygen.

 

  1. What is the maximum number of electrons that can be found in the f orbital?
  1. 2
  2. 4
  3. 6
  4. 8
Show Answer
The correct answer is A!

An orbital can hold at most two electrons with opposite spins. The f here names the orbital’s type (ℓ = 3), not the whole subshell. Larger numbers like 4, 6, or 8 would require multiple f orbitals.