Four separate boxes (I–IV) are intended to show the particulate structures of aqueous…
CHEMISTRY · Subjective · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
Four separate boxes (I–IV) are intended to show the particulate structures of aqueous solutions prepared by dissolving the indicated solute in water. A brief verbal description of each box is provided. Assume the box volume is the same in all four cases.
Box I: CH3OH(aq)
• 40 water molecules plus 5 intact CH3OH molecules are present. Water molecules form hydrogen bonds to the O–H group of methanol by orienting their hydrogen atoms toward the methanol oxygen.
Box II: Ca(NO3)2(aq)
• 4 Ca²⁺ ions and 8 NO3⁻ ions are present among 35 water molecules. Water molecules around the Ca²⁺ ions are drawn with their oxygen atoms pointing toward Ca²⁺. Water molecules around each NO3⁻ ion are drawn with their oxygen atoms pointing toward the ion.
Box III: C6H12O6(aq)
• 10 glucose molecules, each depicted intact, are present among 30 water molecules. Around every glucose molecule, water molecules are oriented so that their hydrogens point toward the multiple –OH groups on glucose.
Box IV: NaCl(aq)
• 6 Na⁺ ions and 6 Cl⁻ ions are present among 25 water molecules. Around each Na⁺ ion the oxygen atoms of water point toward the cation, whereas around each Cl⁻ ion the hydrogen atoms of water point toward the anion. In addition, 2 undissociated NaCl formula units are present.
(a) For EACH box, state whether the diagram accurately follows accepted particulate representation conventions for the specified solute. Your answer should be either “accurate” or “inaccurate” for each of the four boxes.
(b) For every box you labeled “inaccurate” in part (a), identify one specific representational error and explain why it is incorrect in terms of either dissociation behavior or intermolecular/ion–dipole interactions.
(c) Select ONE box that you judged inaccurate and describe how you would redraw it correctly. Address dissociation (if applicable), relative numbers of particles, and the proper orientation of surrounding water molecules.