An instructor carries out the following demonstration to introduce dilution at the…
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
An instructor carries out the following demonstration to introduce dilution at the particle level.
Step 1: A beaker contains 50.0 mL of an aqueous sodium bromide solution. A student counts 40 Na⁺ ions and 40 Br⁻ ions in the fixed-volume diagram that represents this beaker.
Step 2: The entire 50.0 mL portion is poured into a 250 mL volumetric flask, and water is added to the calibration mark, giving a final solution volume of 250 mL.
(a) Describe qualitatively how the particle diagram of the diluted solution must differ from that of the original 50.0 mL solution, assuming the same fixed-volume box is used for both diagrams.
(b) Calculate the total number of Na⁺ ions and Br⁻ ions that should appear in the diluted diagram for the fixed-volume box if the particle representation scales directly with concentration. Show your reasoning.
(c) Explain why simply enlarging the box in the original diagram would be an inappropriate way to represent the diluted solution at the particle level.
(d) If the instructor instead removed 10.0 mL of the original solution without adding any water and represented that 10.0 mL sample in the same fixed-volume box, predict whether the number of solute particles drawn would increase, decrease, or stay the same compared to the original diagram. Justify your prediction.