Indicate which compound in each of the following pairs is...

Key Concepts

Ion Pairing

Ion pairing refers to the reversible association between oppositely charged ions in solution. This phenomenon occurs when the attractive Coulomb forces between ions overcome the forces of solvation by the solvent. Understanding ion pairing is critical when evaluating electrolyte behavior in polar solvents like water, where a balance between solvation and interionic attractions governs the stability of these pairs.

Coulombic (Electrostatic) Interactions

Coulombic interactions describe the force of attraction or repulsion between charged particles. In aqueous solutions, the strength of these attractions depends on factors such as the magnitude of the ionic charges and the distance between them. Stronger electrostatic attractions, arising from higher charges or closer proximity, can increase the propensity for ion pairing despite the diluting and weakening influence of the solvent’s dielectric constant.

Hydration and Solvation Energy

Hydration refers to the interaction between ions and water molecules, leading to solvation. High hydration energy means that water molecules strongly stabilize ions, keeping them separated in solution. Conversely, lower hydration energy reduces the solvent’s effectiveness in isolating ions, potentially enhancing the likelihood of ion pairs forming. This concept is central to predicting ion pairing tendencies based on how effectively water can solvate different ions.

Ionic Charge Density

Ionic charge density is a measure of the charge of an ion relative to its size. Ions with high charge density tend to strongly interact with solvent molecules, often leading to higher hydration energies that counteract the formation of ion pairs. However, when charge density differences between ions exist, they affect the balance between solvation and interionic attractions, thereby influencing the likelihood of ion pairing in solution.

Transcript

00:01 Hi, everyone.

00:01 Thanks for joining me, ms.

00:03 Hulstrom, for a brief discussion on ion pairs as they are related to colligative properties with solutes that are electrolytes.

00:12 As a very quick review, colligative properties are properties that depend on the number of solute particles.

00:28 Electrolites are, for our purposes, ionic substances, that dissociate to two or more particles.

00:51 In an ideal solution, a substance like sodium chloride would dissociate into one sodium cation and one chloride anion, two particles.

01:11 In an ideal solution, the vanthoff factor i for sodium chloride would be two.

01:20 We know that it's actually about, i think, our text says it's 1 .9.

01:28 Why is it less than 2? because of ion pairs that form.

01:37 Some of the sodiums.

01:39 And some sodium ions, switch colors here, some of the sodium ions and some of the chloride ions do not dissociate or they reassociate.

01:52 So i've got nacl that acts as one particle.

01:56 Depending on how many ion pairs are formed, our vant haft factor might be greatly or just slightly affected by the ion pair formation.

02:11 For i have pear formation, highly charged particles such, for instance, magnesium, which is 2 plus aluminum with a 3 plus.

02:28 Oh, how about like sulfate with a 2 minus, phosphate with a 3 minus charge.

02:36 These are going to have a greater tendency.

02:40 These substances that are highly charged have a higher tendency to be a higher tendency to, participate in ion pair formation.

02:55 Let's take a look and evaluate some pairs here.

02:59 First, let's ask ourselves whether sodium chloride, nacl, or sodium sulfate, which of these two would be more likely to form ion pairs? well, we just on our previous slide, learned that this sulfate with a two minus charge tends to form ion pairs.

03:27 If we looked at the vantaf factors, i told you that this one was 1 .9 actual...

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