Coordination Compounds and Biomolecules Quiz Quiz

Challenge your understanding of coordination compounds and biomolecules with this targeted quiz featuring medium-level questions. Explore key principles, naming conventions, biological functions, and structural aspects relevant to both inorganic and biological chemistry.

1. IUPAC Nomenclature in Coordination Compounds

   What is the correct IUPAC name for the complex [Co(NH3)5Cl]Cl2, where the central cobalt ion is coordinated by five ammonia molecules and one chloride ion?

   1. Pentaminechlorocobalt(II) chloride
   2. Pentaamminechloridocobalt(III) chloride
   3. Pentaaminochlorocobalt(III) chloride
   4. Pentamminechlorocobalt(II) dichloride

   Explanation: The correct answer is 'Pentaamminechloridocobalt(III) chloride' because 'ammine' is the correct ligand name for NH3, and the complex contains five ammonia and one chloride ligand. The metal oxidation state in this case is +3, shown as (III). 'Pentamminechlorocobalt(II) dichloride' and 'Pentaminechlorocobalt(II) chloride' use incorrect ligand names or oxidation states, and 'Pentaaminochlorocobalt(III) chloride' uses 'amino' instead of the correct 'ammine'. The order of ligands is also crucial in IUPAC naming.

2. Biomolecules – Proteins Structure

   Which type of chemical bond primarily stabilizes the secondary structure of proteins such as α-helices and β-sheets?

   1. Ionic bonds
   2. Hydrogen bonds
   3. Disulfide bonds
   4. Peptide bonds

   Explanation: Hydrogen bonds are primarily responsible for maintaining the α-helices and β-sheets in the secondary structure of proteins by stabilizing the polypeptide backbone. Ionic bonds occur between charged side chains and are more important in tertiary structure, while disulfide bonds connect different parts of the chain or different chains covalently, affecting tertiary or quaternary structure. Peptide bonds link amino acids together to form the primary structure, not secondary structure.

3. Chelates and Stability

   Why are chelating ligands such as ethylenediamine more effective than monodentate ligands like ammonia in forming stable coordination compounds?

   1. Chelating ligands form multiple bonds to the central metal atom, increasing complex stability
   2. Chelating ligands react faster with metal ions
   3. Chelating ligands are always larger than monodentate ligands
   4. Chelating ligands carry a net positive charge

   Explanation: Chelating ligands bind through two or more donor atoms, creating ring structures and thus increasing the stability of the complex—an effect known as the chelate effect. Size alone does not define a chelating ligand, so the second option is irrelevant. While chelation may affect reaction rates, increased stability is the main distinguishing factor. Most chelating ligands are neutral or negatively charged, not positively charged.

4. Carbohydrates – Reducing Sugars Identification

   Which of the following carbohydrates is classified as a reducing sugar and can react with Tollens' reagent to produce a silver mirror?

   1. Cellulose
   2. Glucose
   3. Sucrose
   4. Glycogen

   Explanation: Glucose is an example of a reducing sugar and can reduce Tollens' reagent to produce metallic silver, as it contains a free aldehyde group in solution. Sucrose is a non-reducing sugar because its glycosidic bond blocks the reactive groups. Cellulose and glycogen, while made of glucose units, do not have free reducing ends readily available to react in the same test.

5. Biological Significance of Metal Ions

   Which metal ion is essential for the oxygen-carrying capacity of hemoglobin in human blood?

   1. Magnesium(II)
   2. Zinc(II)
   3. Iron(II)
   4. Copper(II)

   Explanation: Iron(II) is the core metal ion in the heme group of hemoglobin and is directly responsible for binding oxygen in the bloodstream. Magnesium ions are important in enzymes and chlorophyll but do not carry oxygen. Copper(II) is essential for certain enzymes but is not involved in hemoglobin. Zinc(II) is also important enzymatically, but not related to oxygen transport.