Week 2, Tuesday

BC 1 Week 2 Slides F 2024 pdf

Solvent-solute interactions between water molecules and NaCl allow solids to dissolve

Viscosity:

  • SAE40- higher number, higher viscosity, slower pouring

  • SAE10- lower number, lower viscosity, faster pouring

Because adhesive properties > cohesive, H2O molecules adhere to the wall more than to each other, forming a concave surface

Because cohesive properties > adhesive, Hg atoms at the surface adhere to the wall less than to each other, forming convex surface

On any surface molecule, there is no upward force to cancel the downward force which means each surface molecule “feels” a net downward pull

On any interior molecule, each force is balanced by a force pulling in the opposite direction, which mean that interior molecules “feel” no net pull in any way

All molecules can exhibit dispersion forces

  • Atoms

  • Nonpolar molecules

  • Polar molecules without OH, NH or HF groups

    • Also, Dipole-dipole interactions

  • Polar molecules with OH, NH, or HF groups

    • Also, Dipole-dipole interactions

    • Also, Hydrogen bonding

  • Ionic solids dissolved in polar liquids (like NaCl in H2O)

    • Also, Ion-dipole interactions

Solubility:

  • solute +solvent = solution

  • △Hsoln = △Hsolute + △Hsolvent + △Hmix

    • The overall enthalpy change, △Hsoln is the sum of the three steps

  • Exothermic solution process:

    • When the heat and energy was put into the process of making the solution through the solvent and solute, but ultimately by the end of the process, the heat and energy was lost

  • Endothermic solution process:

    • When the heat and energy was put into the process of making the solution through the solvent and solute, the solution slightly cools and energy is lost, but ultimately by the end the solution still contains more energy than the original values of the solvent and the solute individually

  • Like deserves like

    • A hydrogen bonded solvent will dissolve a hydrogen bonded solute

    • Water is a very good solvent

      • It will dissolve something that is a dipole, hydrogen bonded, and an ion

      • Water will not dissolve molecules that only have dispersion forces though

    • Whether something will be dissolved or not depends on their molecular interaction forces

As molecules get bigger, they will display intermolecular forces throughout different regions of the molecule

Hexadecenoic (palmitic) acid:

  • Amphipathic (polar portion of the molecule and a non-polar portion)

  • Only has dispersion forces

  • Not entirely soluble in water

A molecule that forms a Dimer will have a higher boiling point than one that doesn’t

Critical Micelle concentration: when there is a high concentration of Amphiphiles in water, forming an arrangement (Micelle) where the hydrophobic ends all move to the center, and the hydrophilic ends form a circle around them

  • The Micelle creates an environment inside, where the hydrophobic ends are protected from the water

  • this causes the water to become cloudy

  • This happens with oils and lipids

  • Micelles are important with soap

    • Soap forms micelles around oil or dirt, allowing water to rinse it

  • Micelles cannot be dissolved in water because they are too large, but they will go along with water easily

  • The inside of the Micelle is a hydrophobic environment with dispersion forces.

  • Going from Micelle to random distribution is endothermic (right to left)

    • Final Energy is higher

  • Going from random distribution to Micelle is exothermic (left to right)

    • Final Energy is lower

  • This is because the left side of the equation is higher in energy, than the right side

Electrolyte:

  • a solute which, when dissolved in water, produces a solution that conducts electricity

Strong electrolyte:

  • 100% of the solute dissociates into ions. Usually ionic compounds

  • I.e. NaCl ⇁ Na+ + Cl-

  • There is no NaCl in solution, only Na+ ions and Cl- ions

Weak electrolytes:

  • less than 100% of the solute dissociates into ions. Some of the molecular solute remains undissociated

  • Most of the weak electrolytes we encounter will be weak acids

  • I.e. CH3COOH ⇋ H+ + CH3COO-

    • The ions H+ and CH3COO- as well as an amount of the molecule CH3COOH are all in solution

    • Everything is soluble

  • If aren’t HA dissociates 25% and agent HB dissociates 50%, both are weak electrolytes, but HB is a stronger electrolyte than HA because it dissociates to a greater extent

Non-electrolyte:

  • Molecular substances like glucose, C6H12O6 that dissolve readily in water but don’t dissociate into ions at all are called non-electrolytes


This Thursday’s Quiz is on material is everything from the first day up until but excluding electrolytes.

Will be 5 questions, multiple choice

Will be in the last 10 minutes of class