Solubility and Molarity

Solubility:

Saturated Solution:

• Maximum amount of solute has been dissolved in the solvent at that temperature

• The solution has reached a state of equilibrium

• Rate of dissolution = rate of crystallization (dissolving = crystalizing)

• So, there is a constant concentration of solute dissolved in a saturated solution because the rate of dissolving/undissolving is the same

• The maximum amount of solute that is dissolved in a saturated solution is different for every substance

• One can measure the solubility of a substance by max grams of solute dissolved divided by 100g of water

  \n

Unsaturated Solution:

• Less than the maximum amount of solute possible

• More solute can be dissolved in the solution (when it is below the curve)

• The line is the max at which it can dissolve

  \n

Supersaturated Solution:

• More solute than is normally possible in a saturated solution

• Unstable solution with more solute dissolved than a saturated solution at that temperature (above the curve but all dissolved)

• To disturb, add a little extra solid, bend disk (release a tiny crystal), shake the solution

• To make, heat up the solute-solvent mixture until all the solute dissolves then cool slowly (solid should stay dissolved unless disturbed)

  \n

• For ionics/solids, as temp increases, solubility increases because more entropy

• For covalents/gas, as temp increases, solubility decreases because freeing up gas/less entropy

• For gases, as pressure increases, solubility increases (Henry’s law)

  \n

Molarity:

• A measure of the concentration of a solution

• Moles of solute per liter of solution

• More moles dissolved per liter, more concentrated the solution

• M = moles/L

• Temperature dependent, when temp increases, volume increases

• One uses volumetric flasks to make solutions with precise concentrations

• Use M1V1 = M2V2 when we do not have a solid form of the substance we want to dissolve so we need a very concentrated solution from a chemical company to dilute it and get the molarity we want

• Put it in the volumetric flask, fill to mark, shake to dissolve \n

  \n

Why Ice Melts:

• Freezing point depression

• Salt lowers the freezing point of water

• Normally water is 0 degrees celsius

• Freezing point goes down to below outside temperature

• Ice melts

  \n

Why is pure water easier to freeze than other water?

• Ice has a hexagonal structure

• If particles get in the way/disrupt the formation then it is harder to freeze

• So lower temp is needed

• Freezing point of water is lower when the solution has a higher concentration of the same solute

  \n

Freezing point depression:

• The amount of a freezing point that goes down when a solute is added is not dependent on the identity of the solute but dependent on the concentration of solute particles

• Higher molarity = lower freezing point

  \n

Boiling point elevation:

• The amount the boiling point increases is not dependent on the identity of the solvent but is instead only dependent on the amount of solute
• Higher molarity = highest boiling point
• When more solute is added the boiling point increases

\n

Why do solutions have a higher boiling point than pure water?

• Solutions have more solute in them which makes it harder for water molecules to enter the gas phase.

• The solution has a slower rate of evaporation and low vapor pressure (a measure of the tendency of a material to change into the gaseous or vapour state)

• WHen solute particles are added some reach the upper layer of hte solution so the vapor pressure lowers due to the decrease in solvent molecules at the surface

• Harder for water molecules to evaporate = more energy needed = higher bp

  \n \n

Absorbance:

• Higher concentration means higher absorbance because the proportion of light that gets absorbed is affected by the number of molecules that it interacts with.

• There are more molecules that interact with light

  \n

Scuba Diving:

• When a diver goes underwater, more nitrogen gas dissolves in his blood because Henry’s Law explains that during a dive any gases entering the blood are absorbed in the diver’s blood. There is an increase in solubility because higher pressure

• When the diver comes up pressure decreases and volume increases. Bubbles form in the bloodstream because the gas is trying to escape.

• Increased solubility of a gas at a higher pressure may have narcotic effects because there is too much nitrogen in the bloodstream.

  \n

Van’t Hof Factor:

• Number of particles of th solute that breaks up in solutions

• Count number of particles (check for big ones)

• Ionic compounds are one

• Multiply by molarity

  \n

\
\n