Chemistry - Chapter 12 & 13 - Solutions

Homogenous Mixtures

A mixture that contains two or more substances, and it is not possible to distinguish the substances from one another

Solute

The substance that dissolves

Solvent

The substance that does the dissolving

Suspensions

- type of heterogenous mixture

- Mixtures with large particles that will settle to the bottom when left alone

- can be filtered

- Ex. Soil in water appears cloudy at first, but gravity makes all dirt particles go to bottom

Colloids

- type of Heterogenous Mixture

- Mixtures with medium size particles that won't settle

- Ex. Milk, butter

Electrolytes

When a substance dissolves in water and breaks into charged particles

- Charges can conduct electricity

- Ex. NaCl breaks into Na+ and Cl-

Nonelectrolytes

Substances that don't break into ions

- Ex. Sugar

Soluble

- capable of being dissolved

- creates a solution

- limit to the amount per volume

Insoluble

- Not able to be dissolved

- Creates a heterogenous mixture

Solvation

The process of surrounding solute particles with solvent particles to form a solution.

Ex.

*As long as attraction between Na and O, or Cl and H is stronger than attraction of Na and Cl, then it will break apart (intermolecular forces)

"Like dissolves like",

- something that is polar has to dissolve other polar things

- Nonpolar dissolves other nonpolar things

- Water is a universal solvent, since its a polar molecule, it'll disolve most stuff, except iodine

Why do some things dissolve and others don't

Factors affecting Solvation

- Agitation (stirring it)

- Surface Area (increased surface area = dissolve faster)

- Temperature (Hotter it is, more particles will move around, help break it down)

Temperature and solvation in gases and solids

- Gases: Increasing temp -> decreases solubility

- Solids: Increasing temp -> increases solubility (most of the time)

Saturated Solution

A solution that contains the MAXIMUM of dissolved solute it can hold for that Temp and Pressure

Unsaturated solution

A solution that contains LESS dissolved solute than it can hold for that Temp and Pressure

Supersaturated Solution

contains MORE dissolved solute that a saturated solute at the same Temp and Pressure

Solubility

The amount of substance that is required to form a saturated solution at a specific temperature and pressure.

- Typically given in grams per gram of water (g/mL)

Solubility of gases & pressure

Solubility does not change much in solids and liquids when pressure is changed

Henry's Law

The solubility of a gas in a liquid is directly proportional to the partial pressure of the gas.

*More pressure = more soluble the gas is

How does energy change when solutions form?

- When a solid dissolves, the solvent breaks the intermolecular forces and SEPARATES the particles

- Can either release or absorb energy depending on the substance being dissolved

Concentration

A way to explain/measure how much stuff is in the solution

4 Ways to calculate concentration

1) percent by mass

2) percent by volume

3) **Molarity

4) Molality

Percent by Mass

(Mass of solute/mass of solution) x 100

Percent by Volume

(Volume of solute/volume of solution) x 100

Molarity

(moles of solute/liters of solution)

- Volume of solution is not the same as volume of solvent. Adding in the solute often changes the total volume by a small amount

- Unit = molar, M, or mol/L

Molality

(Moles of solute/kilograms of solvent)

- Unit = molal, m, or mol/kg

- Can measure with JUST a scale

- Temp doesn't change molality

- Measurement depends on solvent, unlike molarity

- Really only used with water

Stock Solutions

- Another name for concentrated solutions

- They're used to make less concentrated solutions in a lab. We add water to it to dilute it down to a lower (new) concentration.

- # of moles doesn't change

- Equation: M(1)V(1) = M(2)V(2)

Dissociation

When ionic compounds are combined with water, they separate into ions

Ex. NaCl (s) -> Na+ (aq) + Cl- (aq)

* -> = dissolved by water

Precipitation Reactions

Not all ionic compounds will dissolve. Insoluble compounds can be formed by the reaction between ions.

*Instead of saying the solid doesn't dissolve, the ions could actually come together to form the solid

Net Ionic Equation

Simplified version of Total Ionic Equation

- Only includes the compounds that undergo a chemical change

- First write equation that contains all compounds, then cancel out the compounds that appear on both sides

*If everything cancels out, a reaction did not happen

Spectator ions

The compounds that appear on both sides of the total ionic equation that you can cancel out.

Stoichiometry in solutions

- Using the Net Ionic Equation, you can determine how much precipitate is formed

- Quantities of the reactants come from the concentrations of initial solutions

Colligative Properties

Properties of a liquid that depend on the concentration of the solute, but not the identity

- Vapor-Pressure Lowering

*Freezing-Point Depression

*Boiling-Point Elevation

- Osmotic Pressure

Vapor-Pressure Lowering

Adding a solute to water reduces the number of water molecules in a given volume

- A reduced number of molecules means that fewer molecules will convert to gas

- Fewer gas molecules -> vapor-pressure is lower

Freezing-Point Depression

Since vapor pressure is lower, the liquid will freeze ar a lower temperature

Equation: in pic

△T(f) = the difference between freezing points of pure solvent and the solution

K(f) = A constant specific for each solvent

m = molality of IONS, NOT substance

Boiling-Point Elevation

Since vapor pressure is lower, the liquid will boil at a higher temperature

Equation: in pic

△T(b) = difference between boiling points of pure solvent and the solution

K(b) = A constant specific for each solvent

m = molality of IONS

Osmotic Pressure

- Osmosis = movement of water across a semipermeable membrane

- This will occur until concentration is balanced

- Osmotic pressure = the external pressure that must be applied to stop osmosis