Solubility and miscibility Flashcards
Explain the difference between solubility and miscibility.
Solubility: Relative ability of a solute to dissolve into a solvent to form a solution.
Miscibility: Ability to mix a compound with another compound to make a homogenous mixture.
Explain the secondary interactions when NaOH dissolves in water (ion-dipole interaction)
Partial positive charge on water molecules (H) are attracted to and bond with negative charge of OH ion. Partial negative charge on water molecules (O) is attracted to and bonds with the positive Na cation. The water molecules surround the OH and Na ions, and dislodge them from the lattice structure.
If a solution is miscible in hexane but not water, what is the polarity of the substance?
“Like dissolves like”. Polar dissolves polar, non-polar dissolves non-polar. Water is polar, meaning if the solution is miscible in hexane, and not water, it must be non-polar.
What substance is more miscible with water- Methanol or pentanol?
Both molecules have a polar OH region, which is miscible with water. However, pentanol has a much larger non-polar region (hydrocarbon chain). This reduces its ability to form hydrogen bonds with water, as the larger the non-polar region, the harder it is for water to disrupt intermolecular forces around the molecule.
What is the relationship between carbon chain length and miscibility?
Smaller hydrocarbon chains are more miscible with water than long ones. The larger the non-polar region, or size of molecule, the harder it is for solvent molecules to disrupt existing intermolecular forces and form hydrogen bonds with the polar region. Therefore, an increase in molecular mass causes a decrease in miscibility.
Why can a substance be miscible with both water and oil?
A molecule with a polar OH group can form hydrogen bonds with polar water. The molecule would also have a non-polar region (hydrocarbon tail) which can form dispersion forces with oil soluble substances. Therefore, it is miscible with both.
