Test: Chemistry - 5 - MCAT MCQ

Molarity (M) = (moles of solute/litres of solution)
Molecular weight of NaCl = 23 + 35= 58 g/mol
Moles of NaCl = 580/58 = 10 mol
Therefore, Molarity (M) = 10 mol/2 L= 5 M

In rock salt, which is the common name for sodium chloride (NaCl), the coordination number of the sodium ion (Na⁺) is indeed six. This means that each sodium ion is surrounded by six chloride ions (Cl^-) in its immediate vicinity. Similarly, each chloride ion is surrounded by six sodium ions. This arrangement is known as a face-centered cubic (FCC) structure, where the ions are arranged in a regular and repeating pattern.

• HClO₄, perchloric acid, is indeed considered one of the strongest acids. The high acidity of HClO₄ is attributed to the presence of highly electronegative oxygen atoms. In general, acids with more oxygen atoms tend to be stronger, as the increased electronegativity of oxygen facilitates the withdrawal of electron density from the central atom.
• In the case of HClO₄, the oxygen atoms can readily pull electrons from the central chlorine atom, inducing a polarization of the O-H bond. This polarization weakens the O-H bond, making it easier for the hydrogen atom to dissociate as an H⁺ ion, leading to the formation of ClO₄^-.
• The ability of the oxygen atoms to withdraw electron density and induce the release of H⁺ ions contributes to the strong acidity of HClO₄. However, it is important to note that the strength of an acid can also depend on other factors, such as the stability of the resulting conjugate base.

Rate of a first order reaction, depends only on one of the reactant's concentrations. When the concentration of the reactant is increased by ‘n' times, the rate of reaction is also increased by ‘n' times. The unit of rate constant for the first order reaction is sec-1 or time^-1.
k₁ = rate/ (a-x) = mol.lit^-1sec^-1/ mol.lit^-1 = sec^-1

If the value of enthalpy is negative and the entropy is positive then the reaction is always spontaneous (ΔH = -10, ΔS = +30). If both enthalpy and entropy are negative (ΔH = -10, ΔS = -30), and T < ΔH/ ΔS then the reaction is spontaneous at low temperature.

• Hydrogen, in its most common form, has one proton and one electron in its nucleus. It does not have any neutrons.
• Deuterium, also known as heavy hydrogen, has one proton and one neutron in its nucleus, along with one electron.
• Tritium is a radioactive isotope of hydrogen. It has one proton and two neutrons in its nucleus, along with one electron.
• An alpha particle is not an atom, but rather a type of particle. It consists of two protons and two neutrons, which is equivalent to the nucleus of a helium atom. Therefore, it can be referred to as a helium atom without any electrons.

In the case of ammonia (NH₃), it has a lone pair of electrons on the nitrogen atom, which allows it to act as a nucleophile by donating that lone pair. On the other hand, the other molecules mentioned are not electron pair donors like ammonia. Instead, they are often classified as electrophiles. Electrophiles are molecules or ions that can accept an electron pair from a nucleophile to form new bonds. These molecules have electron-deficient regions or positively charged atoms that can attract and accept an electron pair. Therefore, except for ammonia, the rest of the molecules mentioned can be considered electrophiles. They have regions or atoms that are capable of accepting an electron pair in a chemical reaction.

Half-life period of the first order reaction can be calculated using the following formula, which is derived from the first order rate law.
t_1/2 = 0.693/k₁ seconds.
Therefore, t1_/2 = 0.693/ 0.45 sec^-1 = 1.54 seconds.

• The exclusion principle indeed states that it is impossible for any two electrons in a given atom to have all four quantum numbers identical. This principle, formulated by Wolfgang Pauli, helps explain the electron configuration and the distribution of electrons in atomic orbitals.
• Hund's rule states that electrons in a sublevel will occupy separate orbitals with parallel spins before pairing up. In other words, when there are multiple orbitals available at the same energy level, electrons will fill them one by one with the same spin until each orbital has one electron. This rule explains the phenomenon of degenerate orbitals and the stability of half-filled and fully filled sublevels.
• The Aufbau principle, also known as the building-up principle, states that in the ground state of an atom, electrons fill the orbitals in order of increasing energy. This principle describes the sequential filling of electron shells and subshells based on their relative energies.
• The uncertainty principle, formulated by Werner Heisenberg, states that it is impossible to simultaneously determine the exact position and momentum of a particle with high precision. This principle highlights the fundamental limitations in the measurement of certain pairs of physical properties of particles, such as position and momentum or energy and time.
• All of these principles play important roles in understanding the behavior of electrons in atoms and the fundamental principles of quantum mechanics.

A gas with the greater ‘a' value will liquefy easily. Here NH₃ has greater ‘a' value than the other gases. Therefore, it will liquefy easily.

Colligative properties refer to properties that are dependent solely on the amount of solute present, regardless of its specific identity. Among the four properties mentioned, only osmotic pressure is influenced by the amount of solute, while the other properties remain unaffected by changes in solute concentration.

A reduction reaction occurs when an atom or ion accepts an electron, while an oxidation reaction occurs when an atom or ion releases an electron. In the first mentioned reaction, the Cu²⁺ ion accepts two electrons, indicating a reduction process. Conversely, in the second reaction, the Cu atom releases two electrons, indicating an oxidation process.

The atomic mass of any atom is less than the sum of the protons, neutrons and electrons present in it. This defect in the mass is measured by the binding energy. Binding energy of an atom can be calculated using the equation ΔE = Δmc² , where ΔE – energy liberated, Δm – loss of mass and cspeed of light in vacuum.

The ratio of relative abundance of two molecular ion peaks of a chlorine atom in mass spectroscopy is M⁺ : (M+2) = 1:3, because the natural abundance of chlorine is higher than other elements. The natural abundance of chlorine is Cl3⁵ - 75.77% and Cl³⁷t- 24.23%.

In general, if E^o_cell is positive, the reaction is feasible. If E^o_cell is negative, the reaction is not feasible. Here, the E^o_cell of the reaction I is negative, therefore the reaction is not feasible and E^o_cell of the reaction II is positive, therefore the reaction is feasible.