A researcher investigates how adding ethanol to water influences the dissolution of…
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
A researcher investigates how adding ethanol to water influences the dissolution of ionic compound KBr. A fixed-volume particulate diagram of the resulting ternary liquid mixture is described below.
• 65 V-shaped particles consisting of one red and two white atoms (water molecules).
• 20 bent molecules, each composed of two black atoms and one red atom (ethanol molecules). The black atoms form a two-carbon chain; the red atom is bonded to one of the black atoms through an O–H group.
• 6 purple spheres (K⁺ ions) and 6 green spheres (Br⁻ ions), all fully separated from each other.
• Around each purple sphere, several water molecules are oriented so that their oxygen atoms face the ion, whereas around each green sphere several water molecules are oriented with their hydrogen atoms directed toward the ion.
• Ethanol molecules are interspersed randomly and show no preferred orientation around the ions.
Respond fully to the prompts below.
(a) Identify the primary solvent, the co-solvent (if any), and the solute(s) present in the mixture.
(b) Explain, with reference to the molecular polarity of water, why the orientations of water molecules differ around K⁺ and Br⁻ ions.
(c) Predict how doubling the number of ethanol molecules while keeping all other particle counts constant would affect the ion–solvent interactions depicted. Provide a molecular-level justification.
(d) Propose one change that could be made to the particulate diagram to depict a more concentrated solution of KBr, and explain why your change is chemically reasonable.