Malen Bara



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Qualification Master
Subject CHEMISTRY
Country Morocco
Gender Male
Malen Bara CHEMISTRY   -   Inorganic Chemistry

Which of the following methods is commonly used to synthesize graphene?

Chemical vapor deposition (CVD) is a common method used to synthesize high-quality graphene. This process involves the deposition of carbon atoms onto a substrate from a gas-phase precursor, resulting in the formation of a graphene layer.
Malen Bara CHEMISTRY   -   Inorganic Chemistry

Which of the following is a typical example of an inner-sphere electron transfer reaction?

An inner-sphere electron transfer involves a bridging ligand that temporarily connects the two reactants. In the reduction of MnO₄⁻ by Fe²⁺, an intermediate complex can form where a ligand bridges the Mn and Fe centers, facilitating the electron transfer.
Malen Bara CHEMISTRY   -   Inorganic Chemistry

Which of the following compounds acts as both a Lewis acid and a Lewis base?

Water (H₂O) can act as both a Lewis acid (accepting a pair of electrons when it forms H₃O⁺) and a Lewis base (donating a pair of electrons when it acts as a solvent or forms coordinate bonds). The other compounds typically act only as Lewis acids or bases.
Malen Bara CHEMISTRY   -   Inorganic Chemistry

Which of the following actinides is commonly used as a fuel in nuclear reactors?

Uranium, specifically U-235, is commonly used as a fuel in nuclear reactors due to its ability to undergo fission and release a significant amount of energy. Thorium can also be used in nuclear reactors, but it is less common compared to uranium.
Malen Bara CHEMISTRY   -   Inorganic Chemistry

Which of the following transition metals exhibits the highest number of oxidation states?

Manganese exhibits the highest number of oxidation states, ranging from -3 to +7. This wide range of oxidation states is due to its electronic configuration, which allows it to lose or share various numbers of electrons.
Malen Bara CHEMISTRY   -   Inorganic Chemistry

Which of the following elements forms a stable diatomic molecule in the gas phase?

Nitrogen forms a stable diatomic molecule (N₂) due to the formation of a strong triple bond between the two nitrogen atoms, making it very stable. The other elements listed typically form more complex molecular structures or allotropes.
Malen Bara CHEMISTRY   -   Inorganic Chemistry

Which metal ion is at the active site of the enzyme carbonic anhydrase?

Carbonic anhydrase is an enzyme that catalyzes the hydration of carbon dioxide. The active site of this enzyme contains a zinc ion (Zn²⁺) which is coordinated by three histidine residues and a water molecule, playing a crucial role in the enzyme's catalytic function.
Malen Bara CHEMISTRY   -   Inorganic Chemistry

In the compound ferrocene (Fe(C5H5)2), what is the oxidation state of the iron center?

In ferrocene, each cyclopentadienyl anion (C5H5⁻) is considered to donate 6 electrons to the iron atom, providing a total of 12 electrons. Iron in the neutral state (Fe) has 8 valence electrons, leading to the 18-electron configuration that stabilizes the complex. Hence, the oxidation state of iron in ferrocene is 0.
Malen Bara CHEMISTRY   -   Inorganic Chemistry

Which of the following ligands will cause the greatest splitting in the d-orbital energies of a central metal ion according to the spectrochemical series?

According to the spectrochemical series, CN⁻ is a strong field ligand and causes significant splitting of the d-orbitals in a central metal ion. This large splitting can lead to different electronic configurations and affects the color and magnetic properties of the complex.
Malen Bara CHEMISTRY   -   Inorganic Chemistry

In a face-centered cubic (fcc) lattice, what is the coordination number of each atom?

In a face-centered cubic (fcc) lattice, each atom is surrounded by 12 nearest neighbors. This coordination number of 12 arises because each atom touches four atoms in its own layer, four atoms in the layer above, and four atoms in the layer below.
Malen Bara CHEMISTRY   -   Inorganic Chemistry

Which of the following molecules has the most polar bond?

Polarity of a bond is determined by the difference in electronegativity between the two bonded atoms. Fluorine is the most electronegative element, and the electronegativity difference between hydrogen and fluorine is the greatest among the given pairs, making HF the most polar bond.
Malen Bara CHEMISTRY   -   Inorganic Chemistry

Which of the following elements has the highest second ionization energy?

The second ionization energy is the energy required to remove the second electron after the first has been removed. Sodium has a very high second ionization energy because removing the second electron means disrupting a stable noble gas configuration (Ne), making it significantly more difficult than the first ionization.
Malen Bara CHEMISTRY   -   Organic Chemistry

Which of the following principles is not one of the Twelve Principles of Green Chemistry?

Increasing chemical yields is not explicitly one of the Twelve Principles of Green Chemistry. While yield is important, the principles focus on reducing waste, minimizing the use of hazardous substances, and designing environmentally benign processes.
Malen Bara CHEMISTRY   -   Organic Chemistry

Which type of enzyme catalysis involves the formation of a covalent bond between the enzyme and the substrate?

In covalent catalysis, a transient covalent bond is formed between the enzyme and the substrate during the reaction. This temporary covalent intermediate helps stabilize the transition state and lower the activation energy of the reaction.
Malen Bara CHEMISTRY   -   Organic Chemistry

Which of the following heterocycles contains nitrogen and is aromatic?

Pyrrole is a five-membered heterocyclic compound containing nitrogen and is aromatic. It has a planar structure with a conjugated system of (4n+2) π-electrons, making it aromatic according to Huckel's rule.
Malen Bara CHEMISTRY   -   Organic Chemistry

Which of the following statements about the polymerization of ethylene to form polyethylene is correct?

The polymerization of ethylene to form polyethylene is typically carried out via a free radical mechanism. This process involves the initiation, propagation, and termination steps, where free radicals mediate the addition of ethylene monomers to the growing polymer chain.
Malen Bara CHEMISTRY   -   Organic Chemistry

In an electrophilic aromatic substitution reaction, which intermediate is formed?

In electrophilic aromatic substitution, the intermediate formed is a sigma complex (also known as an arenium ion or Wheland intermediate). This intermediate features a partially positive charge and a disrupted aromatic system, which is later restored upon deprotonation.
Malen Bara CHEMISTRY   -   Organic Chemistry

Which of the following compounds is not aromatic?

Benzene, pyridine, and naphthalene all obey Huckel's rule for aromaticity, possessing (4n+2) π-electrons and a planar structure. Cyclooctatetraene, however, does not adopt a planar conformation and does not have (4n+2) π-electrons, making it non-aromatic.
Malen Bara CHEMISTRY   -   Organic Chemistry

In proton NMR spectroscopy, what splitting pattern would you expect for the protons on the methylene group in ethyl acetate (CH3COOCH2CH3)?

The methylene group (CH2) in ethyl acetate is adjacent to a methyl group (CH3), which causes spin-spin coupling. The three protons of the methyl group split the signal of the two methylene protons into a quartet due to the n+1 rule (n=3).
Malen Bara CHEMISTRY   -   Organic Chemistry

What is the first step in the retrosynthetic analysis of 1-bromo-2-phenylethane?

Retrosynthetic analysis involves breaking down the target molecule into simpler precursor structures. For 1-bromo-2-phenylethane, identifying how the phenyl group is attached to the ethane chain is crucial for determining the precursor molecules. In this case, one might consider the synthesis from ethylbenzene or from styrene via bromination.
Malen Bara CHEMISTRY   -   Organic Chemistry

In which of the following reactions does the formation of a carbocation intermediate occur?

The SN1 reaction mechanism involves two steps. The first step is the dissociation of the leaving group, leading to the formation of a carbocation intermediate. This carbocation then reacts with a nucleophile in the second step.
Malen Bara CHEMISTRY   -   Organic Chemistry

Which of the following compounds is chiral?

2-Butanol has a carbon atom (the second carbon) attached to four different groups: a hydroxyl group (-OH), a methyl group (-CH3), an ethyl group (-CH2CH3), and a hydrogen atom. This makes it chiral, possessing non-superimposable mirror images (enantiomers).
Malen Bara CHEMISTRY   -   Organic Chemistry

Which of the following functional groups can act as both an acid and a base?

Amines contain a nitrogen atom with a lone pair of electrons, which allows them to act as a base by accepting a proton. They can also act as weak acids by donating a proton from the hydrogen atoms attached to the nitrogen, although this is less common compared to their basicity.
Malen Bara CHEMISTRY   -   Organic Chemistry

Which of the following statements about the bonding in ethyne (acetylene, C2H2) is correct?

In ethyne, each carbon atom is sp hybridized, forming a linear molecule with a bond angle of 180 degrees. The carbon atoms are connected by a triple bond consisting of one sigma bond and two pi bonds.