Intermolecular Forces and Solubility in GOB Chemistry

Intermolecular Forces and Solubility

Theory of "Likes Dissolve Likes"

In chemistry, the principle of "likes dissolve likes" states that compounds with similar intermolecular forces or polarity will dissolve into each other. This concept is essential for predicting solubility and the formation of homogeneous mixtures.

• Homogeneous mixture: A solution where the components are uniformly distributed.

• Heterogeneous mixture: A mixture where the components are not uniformly distributed.

• Solution: A homogeneous mixture of two or more substances.

Key Point: Polar compounds tend to dissolve in polar solvents, and nonpolar compounds dissolve in nonpolar solvents.

Types of Intermolecular Forces

Main Types of Forces

Intermolecular forces are the attractions between molecules that affect physical properties and solubility.

• London Dispersion Forces: Weak forces present in all molecules, especially nonpolar ones.

• Dipole-Dipole Interactions: Occur between polar molecules due to their permanent dipoles.

• Hydrogen Bonding: A strong type of dipole-dipole interaction occurring when hydrogen is bonded to highly electronegative atoms (N, O, F).

Predicting Solubility: Examples

Identifying Intermolecular Forces and Solution Formation

To predict whether a solution will form, identify the intermolecular forces present in both the solute and solvent.

• a) CCl4 and P4: - Both are nonpolar. - London dispersion forces are present. - Solution forms: Yes, because both are nonpolar.

• b) CH3OH and CH4: - CH3OH is polar and can form hydrogen bonds. - CH4 is nonpolar (London dispersion only). - Solution forms: No, because polar and nonpolar do not mix well.

• c) CH3CH2OH and HF: - Both can form hydrogen bonds. - Both are polar. - Solution forms: Yes, because both are polar and can hydrogen bond.

• d) I- and NH3: - NH3 is polar and can hydrogen bond. - I- is an ion. - Solution forms: Yes, because ions and polar molecules can interact (ion-dipole forces).

Practice Statements: Solubility Predictions

Evaluating Solubility Based on Intermolecular Forces

• a. Methane will dissolve completely in acetone, CH3COCH3: - Methane is nonpolar; acetone is polar. - Prediction: Methane will not dissolve completely in acetone.

• b. Hydrofluoric acid (HF) will form a heterogeneous mixture with tetrachloride, CCl4: - HF is polar and can hydrogen bond; CCl4 is nonpolar. - Prediction: They will not mix; a heterogeneous mixture forms.

• c. Pentane will form a homogeneous mixture with CBr4: - Both are nonpolar. - Prediction: They will mix; a homogeneous solution forms.

• d. Methanethiol (CH3SH) is miscible in fluoromethane (CH3F): - CH3SH is polar; CH3F is polar. - Prediction: They are likely to be miscible due to similar polarity.

Summary Table: Solubility and Intermolecular Forces

Solute	Solvent	Type of Forces	Solution Forms?
CCl4	P4	London dispersion	Yes
CH3OH	CH4	Hydrogen bonding vs. London dispersion	No
CH3CH2OH	HF	Hydrogen bonding	Yes
I-	NH3	Ion-dipole, hydrogen bonding	Yes
Methane	Acetone	Nonpolar vs. polar	No
HF	CCl4	Polar vs. nonpolar	No
Pentane	CBr4	Nonpolar	Yes
Methanethiol	Fluoromethane	Polar	Yes

Key Equations

• General Solubility Rule: $\text{Polar solute} + \text{Polar solvent} \rightarrow \text{Solution}$ $\text{Nonpolar solute} + \text{Nonpolar solvent} \rightarrow \text{Solution}$ $\text{Polar solute} + \text{Nonpolar solvent} \rightarrow \text{No solution}$

Additional info: Some context and chemical structures were inferred based on standard GOB Chemistry curriculum and the visible content.