Like Dissolves Like

Summary

This demonstration illustrates the principle of 'like dissolves like,' showing that polar solvents dissolve polar solutes, while non-polar solvents dissolve non-polar solutes. Using water (polar) and hexane (non-polar) as solvents, and copper(II) chloride (ionic/polar) and iodine (non-polar) as solutes, the experiment visually demonstrates solubility differences. Water dissolves copper(II) chloride but not iodine, whereas hexane dissolves iodine but not copper(II) chloride. The separation of layers highlights density differences, and the experiment is conducted in a fume hood for safety. This simple yet effective demonstration reinforces fundamental chemical concepts of polarity and solubility.

Takeaways

• 😀 Polar solvents dissolve polar solutes, and non-polar solvents dissolve non-polar solutes — 'like dissolves like.'
• 😀 Water is a polar molecule with a partial negative charge on oxygen and partial positive charges on hydrogen.
• 😀 Sodium chloride (table salt) is an ionic compound made of charged ions that dissolve in polar solvents like water.
• 😀 In water, positive hydrogen ends attract negative ions, and negative oxygen ends attract positive ions, allowing ionic compounds to dissolve.
• 😀 Hexane is a non-polar molecule composed of carbon and hydrogen, with no positive or negative ends.
• 😀 Non-polar substances dissolve in other non-polar substances through London dispersion forces and entropy.
• 😀 Water and hexane do not mix and form separate layers due to differences in polarity and density.
• 😀 Iodine dissolves in hexane (non-polar) but not in water (polar).
• 😀 Copper(II) chloride dissolves in water (polar) but not in hexane (non-polar).
• 😀 The experiment visually demonstrates that polar solvents selectively dissolve polar solutes, and non-polar solvents selectively dissolve non-polar solutes.
• 😀 Hexane floats on water because its density (0.66 g/mL) is lower than that of water (1 g/mL).
• 😀 Safety precautions are important: hexane vapors are harmful, so the experiment should be conducted in a fume hood.

Q & A

What is the main principle demonstrated in this experiment?

The experiment demonstrates that polar solvents dissolve polar solutes and non-polar solvents dissolve non-polar solutes, summarized as 'like dissolves like.'

Why is water considered a polar molecule?

Water is polar because it has a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms due to unequal sharing of electrons.

Why can polar solvents dissolve ionic compounds?

Polar solvents can dissolve ionic compounds because the positive end of the solvent molecule attracts negative ions, and the negative end attracts positive ions, pulling them apart from the crystal lattice.

Why does hexane float on water when layered together?

Hexane floats on water because it has a lower density (0.66 g/mL) compared to water (1 g/mL), and the two liquids are immiscible due to their polarity differences.

Why does iodine dissolve in hexane but not in water?

Iodine is non-polar, so it dissolves in non-polar hexane due to London dispersion forces, but it does not dissolve in polar water because there are no strong interactions between them.

Why does copper(II) chloride dissolve in water but not in hexane?

Copper(II) chloride is ionic/polar, so water molecules can surround and separate its ions, dissolving it. Hexane, being non-polar, cannot interact effectively with the ions, so it does not dissolve.

What are London dispersion forces and how do they relate to solubility?

London dispersion forces are weak attractions between non-polar molecules due to temporary shifts in electron density. These forces allow non-polar molecules to dissolve in other non-polar solvents.

Why is the experiment conducted in a fume hood?

The experiment uses hexane, which produces hazardous vapors. A fume hood prevents inhalation of these vapors and ensures safe handling.

What observation confirms the 'like dissolves like' principle in the mixed test tube?

In the mixed test tube, water dissolves copper(II) chloride but not iodine, and hexane dissolves iodine but not copper(II) chloride, confirming that polar solvents dissolve polar solutes and non-polar solvents dissolve non-polar solutes.

How does the structure of hexane explain its non-polarity?

Hexane consists of carbon atoms surrounded by hydrogen atoms, with electrons shared relatively equally and no distinct positive or negative ends, making it non-polar.

What safety precautions are implied for handling hexane in this experiment?

Hexane should be handled in a fume hood to avoid inhalation of vapors, and direct contact should be minimized as it is flammable and potentially harmful.

How does density affect the layering of water and hexane?

Since water is denser (1 g/mL) than hexane (0.66 g/mL), water forms the bottom layer, and hexane floats on top when the two liquids are combined.