Intermolecular Forces and Solubility Chemistry Education Group - - PowerPoint PPT Presentation

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intermolecular forces and solubility
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Intermolecular Forces and Solubility Chemistry Education Group - - PowerPoint PPT Presentation

Nov 18, 2022 174 likes •579 views

Likes Dissolve Likes Intermolecular Forces and Solubility Chemistry Education Group Department of Chemistry & Biochemistry University of Oregon Eugene, Oregon 97403 Substances that exhibit similar types of intermolecular force dissolve in

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SLIDE 1

Likes Dissolve Likes Intermolecular Forces and Solubility

Chemistry Education Group Department of Chemistry & Biochemistry University of Oregon Eugene, Oregon 97403

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Substances that exhibit similar types of intermolecular force dissolve in each other. The general rule: “like dissolves in like.”

Isopropanol water

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SLIDE 3

Solubility Demonstration

Consider the intermolecular forces in

  • water, H2O
  • hexane, C6H14
  • potassium permanganate, KMnO4
  • iodine, I2

Instructional Objectives 1. Identify the major types of IMFs in solutions and their relative strengths. 2. Apply the “likes dissolves likes” rule with identity of IMFs to determine if two substance will form a solution. Predict relative solubilities of substances.

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SLIDE 4

Substance

Polar or non- polar

IMFs hexane (C6H14) water potassium permanganate (KMnO4) iodine (I2)

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SLIDE 5
  • Chemist’s rule of thumb – like dissolves like
  • A chemical will dissolve in a solvent if it has a

similar structure to the solvent.

  • Polar molecules and ionic compounds will be more

soluble in polar solvents.

  • Nonpolar molecules will be more soluble in

nonpolar solvents.

Will It Dissolve?

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SLIDE 6

Substance

Polar or non- polar

IMFs hexane (C6H14) Non-polar dispersion water polar Hydrogen bonding potassium permanganate (KMnO4) ionic Ion-ion iodine (I2) Non-polar dispersion

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SLIDE 7

Solutions

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SLIDE 8

Predict the solubility:

water + hexane

  • A. soluble
  • B. insoluble

Observation

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SLIDE 9

Predict the solubility: water + hexane

  • A. soluble
  • B. insoluble
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Water + Hexane

When water is placed in hexane there are two layers.

  • Explain. Which is on the top?

Hexane C6H14

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Water + Hexane: Not a solu;on

When 6 mL of hexane is placed in 10 mL of water and mixed, two layers are observed. The hexane is non-polar, it is the layer on the top. The density of hexane is 0.654 g/mL at 20°C. Water is polar, it is the layer on the boNom. The density of water is 1.00 g/mL at 20°C. Hexane is mostly not soluble in water. We need to go into more depth and detail in determining what factors govern the dissolving process and what determines if a solu;on will or will not form.

water hexane

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miscible immiscible

  • il + vinegar

water + ethanol

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Why substances dissolve…two factors

  • entropy (S) – always favors solution formation
  • enthalpy (H) – must consider intermolecular forces

Ø solute – solute interactions (ΔHsolute) Ø solvent – solvent interactions (ΔHsolvent) Ø solute – solvent interactions (ΔHmixing)

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SLIDE 14

Consider hexane (C6H14) in H2O: ΔHsolute: ΔHsolvent: ΔHmixing:

dispersion forces hydrogen bonds dipole induced- dipole forces endothermic endothermic exothermic Note: energy released in the mixing step does not balance the energy required to separate the water molecules. ΔHsolution is positive, (entropy is not favorable) and no solution forms. Work with your neighbor to identify the IMFs present in each interaction and if the IMF interaction is exo or endothermic :

hexane-hexane H2O-H2O H2O-hexane

IMF Endo or Exo

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SLIDE 15

ΔHsol’n = ΔHsolute + ΔHsolvent + ΔHmixing > 0

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SLIDE 16

Substance

Polar or non- polar

IMFs water potassium permanganate (KMnO4)

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SLIDE 17

Substance

Polar or non- polar

IMFs water polar Hydrogen bonding potassium permanganate (KMnO4) ionic Ion-ion

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SLIDE 18

Predict the solubility: water + potassium permanganate (KMnO4)

  • A. soluble
  • B. insoluble
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SLIDE 19

Predict the solubility: water + potassium permanganate (KMnO4)

  • A. soluble
  • B. insoluble

water + KMnO4

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SLIDE 20

For example, consider the interactions of 0.5 g KMnO4 (solute) in 10 mL of H2O (solvent) Work with your neighbor to identify the specific interactions and determine which IMFs are present : solute – solute interactions (ΔHsolute) Ø solvent – solvent interactions (ΔHsolvent) Ø solute – solvent interactions (ΔHmixing)

Next, decide whether these interactions are exothermic or endothermic. Next, draw a Born-Haber diagram.

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For example, KMnO4 in H2O:

ΔHsolute ΔHsolvent ΔHmixing ion-ion forces hydrogen bonds ion-dipole forces endothermic endothermic exothermic Energy required to overcome the IMFs in the solute and solvent is comparable to the energy released upon

  • mixing. ΔHsolution is negative Therefore a solution forms.

dissolution of salt animation K+ MnO4- K+ IMF Endo or Exo

MnO4

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ΔHsol’n = ΔHsolute + ΔHsolvent + ΔHmixing < 0

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Predict the solubility: water + iodine

  • A. soluble
  • B. insoluble
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SLIDE 24

Predict the solubility: water + iodine

  • A. soluble
  • B. insoluble
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SLIDE 25

Predict the solubility: water + iodine

  • A. soluble
  • B. insoluble
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SLIDE 26

Predict the solubility: hexane + iodine

  • A. soluble
  • B. insoluble

Ion-induced dipole (3-15)

Hexane C6H14

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SLIDE 27

Substance

Polar or non- polar

Primary IMFs hexane (C6H14) Non-polar dispersion water polar Hydrogen bonding and dipole- dipole potassium permanganate (KMnO4) ionic Ion-ion iodine (I2) Non-polar dispersion

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SLIDE 28

Predict the solubility: hexane + iodine

  • A. soluble
  • B. insoluble
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SLIDE 29

Predict the solubility: hexane + water + iodine

  • A. I2 soluble in hexane
  • B. I2 soluble in water
  • C. I2 not soluble in both
  • D. I2 soluble in both
  • E. I2 don’t know

water Hexane + I2

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Nonpolar molecules will be more soluble in nonpolar solvents.

Will a solution form?

Dispersion (0.05-40)

Hexane and I2 both have dispersion forces only. I2 is soluble in hexane.

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SLIDE 31

I2(s) polar nonpolar

hexane

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Predict the solubility: hexane + potassium permanganate (KMnO4)

  • A. soluble
  • B. insoluble
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SLIDE 33

Predict the solubility: hexane + potassium permanganate (KMnO4)

  • A. soluble
  • B. insoluble
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Solubility Demonstration

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SLIDE 35
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Non-polar will generally not dissolve in polar solvents. Polar will generally not dissolve in non-polar solvents.

Top layer solvent = hexane Bottom layer solvent = water Top layer solute = I2 Bottom layer solute = KMnO4

they don’t mix

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SLIDE 37

Predict the solubility: water + hexane + potassium permanganate

  • A. KMnO4 soluble in hexane
  • B. KMnO4 soluble in water
  • C. KMnO4 not soluble in both
  • D. KMnO4 soluble in both
  • E. KMnO4 don’t know
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SLIDE 38

Predict the solubility: water + hexane + potassium permanganate

  • A. soluble
  • B. insoluble

hexane Water and KMnO4 KMnO4(aq) Ionic compounds can be soluble in polar solvents such as water. Note: MgO(s) is ionic but is not soluble in water. K+ Ion-dipole IMF

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SLIDE 39

Non-polar will generally not dissolve in polar solvents. Polar will generally not dissolve in non-polar solvents.

Top layer solvent = hexane Bottom layer solvent = water Bottom layer solute = KMnO4

they don’t mix

Soluble ionic salts will dissolve in water.

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SLIDE 40

Polar molecules (partial charges) and ionic compounds (full charges) will be more soluble in polar solvents.

Will a solution form?

Consider ionic compounds in water. NaCl for example.

NaCl: ion – ion forces H2O: hydrogen bonds and dispersion

New force is ion-dipole attraction