Problem 22 - Chemistry: Principles and Reactions

Question

Which of the following is more soluble in \(\mathrm{CCl}_{4} ?\) In each case, explain your answer. (a) hexane \(\left(\mathrm{C}_{6} \mathrm{H}_{14}\right)\) or \(\mathrm{CaCl}_{2}\) (b) \(\mathrm{CBr}_{4}\) or \(\mathrm{HBr}\) (c) benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)\) or ethyl alcohol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\) (d) \(\mathrm{I}_{2}\) or \(\mathrm{NaI}\)

Step-by-Step Solution

Answer

a) Hexane (C6H14) or Calcium chloride (CaCl2) b) Carbon tetrabromide (CBr4) or Hydrogen bromide (HBr) c) Benzene (C6H6) or Ethyl alcohol (C2H5OH) d) Iodine (I2) or Sodium iodide (NaI) Answer: a) Hexane (C6H14) b) Carbon tetrabromide (CBr4) c) Benzene (C6H6) d) Iodine (I2)

Step 1: (a) Determine the polarity of hexane and CaCl2

Hexane (C6H14) is a non-polar hydrocarbon. Meanwhile, Calcium chloride (CaCl2) is an ionic compound and thus polar.

Step 2: (a) Compare hexane and CaCl2 with the polarity of CCl4

Carbon tetrachloride (CCl4) is a non-polar compound. Since like dissolves like, hexane, a non-polar compound, is more soluble in CCl4 than the polar compound CaCl2.

Step 3: (b) Determine the polarity of CBr4 and HBr

CBr4 is a non-polar compound due to its symmetric structure. Hydrogen bromide (HBr) is a polar compound because of the electronegativity difference between hydrogen and bromine.

Step 4: (b) Compare CBr4 and HBr with the polarity of CCl4

Since CCl4 is a non-polar compound, it will dissolve the non-polar compound CBr4 better than the polar compound HBr.

Step 5: (c) Determine the polarity of benzene and ethyl alcohol

Benzene (C6H6) is a non-polar hydrocarbon. Ethyl alcohol (C2H5OH) is a polar compound due to the polar hydroxyl (OH) group.

Step 6: (c) Compare benzene and ethyl alcohol with the polarity of CCl4

As CCl4 is a non-polar compound, it will dissolve the non-polar compound benzene better than the polar compound ethyl alcohol.

Step 7: (d) Determine the polarity of I2 and NaI

Iodine (I2) is a non-polar compound since it is composed of two iodine atoms with equal electronegativities. Sodium iodide (NaI) is an ionic compound and thus polar.

Step 8: (d) Compare I2 and NaI with the polarity of CCl4

Because CCl4 is a non-polar compound, it will dissolve the non-polar compound I2 better than the polar compound NaI.

Key Concepts

Polarity of Compounds

Understanding the polarity of compounds is crucial in determining their solubility. In simple terms, polarity refers to the distribution of electric charge around a molecule.
Polar molecules have a positive and a negative end, like a magnet, due to differences in electronegativity between atoms. These uneven charges result from polar bonds.
Non-polar molecules have a more equal distribution of charge.

Key characteristics of polar compounds include:

• Presence of polar bonds (e.g.,

  water, HCl)

• Asymmetrical shape of molecules
• Higher boiling and melting points compared to non-polar compounds

Non-polar compounds are characterized by:

• Symmetrical structure
• Equal sharing of electrons (e.g.,

  O₂, N₂)

• Lower boiling and melting points

By identifying these properties, we can better understand how different substances interact with each other.

Non-polar Compounds

Non-polar compounds do not have a significant difference in electronegativity between their atoms.
This results in an even distribution of electrical charge. Let's understand these compounds a bit further.

They often consist of symmetrical structures, which help evenly distribute the electrons.
Examples include hydrocarbons like hexane and compounds like carbon tetrachloride (CCl₄).

• Structure: Often linear or symmetrical
• Examples include molecules with identical atoms bonded together (e.g., Cl₂)

Non-polar compounds tend to be soluble in other non-polar solvents. This happens because there are no strong attractions or repulsions occurring between the molecules. Instead, they can interact freely without any restraints caused by polar charges.
Knowing whether a compound is non-polar is useful for predicting its solubility behavior.

Like Dissolves Like Principle

The 'like dissolves like' principle is a fundamental concept in chemistry, particularly when predicting solubility.
This principle states that polar compounds tend to be soluble in polar solvents, while non-polar compounds are soluble in non-polar solvents.

This idea is based on the similarity of intermolecular forces.

• Polar compounds have dipole-dipole interactions or hydrogen bonding
• Non-polar compounds engage in dispersion forces

For example, water (a polar solvent) can dissolve salt (a polar compound) easily, but it doesn't dissolve oil (a non-polar compound).

This principle

makes it easier to predict whether one substance will dissolve in another.
By understanding the 'like dissolves like' principle, you can make informed decisions when working with solutions and mixtures in chemical processes.