Week 7 (midterm 3)

Carbon allotropes (most common)

diamond, carbons

Graphite (shape, traits, what holds it together)

• covalent network atomic solid, carbon allotrope

• forms sheets that slide across each other

• soft

• LDFs, no covalent bonds between sheets

Diamond (shape, traits)

• carbon allotrope, covalent network atomic solid

• hard

• strong covalent bonds in a 3D network

Why is diamond hard but graphite soft?

Diamond is tetrahedrally bound to 4 other carbons → creates covalently bonded 3D network (which is strong)

graphite sheets are mobile because there are NO covalent bonds between sheets, only weak LDFs

Buckminsterfullerene (“Bucky ball”) - shape, traits, what holds it together

• covalent network atomic solid, Carbon allotrope

• made of clusters of carbon, like C60, usually 36-100 carbons

• bonded in spherical shapes

• stuck together by LDFs

• soft

Carbon nanotubes (shape, traits)

carbon allotrope, covalent network atomic solid

• light, strong

• cylinder

Silicates (shape, traits, what happens when it’s heated)

Contains silicon and oxygen, covalent network atomic solid

• silicon bonds to 4 oxygen (tetrahedral shape on each)

• if heated → becomes an amorphous solid (no defined shaped)

are silicon and carbon similar or different

very different

Solution

homogenous mix of 2 or more things

• not easily separated

Solute

Substance that gets dissolved, minority component(s) in a solution

Solvent

substance that does the dissolving, majority component(s) of the solution

aqueous solutions

solutions where liquid water is the solvent, and any other solid/liquid/gas is the solute

just memorize the first 2 columns

ok

Entropy

Measurement of energy randomization or energy dispersal in a system

What is the driving force behind the creation of solutions (IF THERE ARE NO OTHER FORCES PRESENT,)

IF THERE ARE NO OTHER FORCES PRESENT, entropy will cause mixtures to mix randomly and evenly

IMFs and entropy

Sometimes, IMFs stop solutions from forming - If IMFs of individual species are stronger than the forces of interspecies mixing, then a solution CAN’T occur

Reason for “like dissolves like”

Due to IMFs

What can dissolve ionic compounds?

Polar species

What do polar vs. non polar substances dissolve?

polar: dissolves polar, ionic

non polar: dissolves non-polar

When can solutions NOT form?

1. If IMFs of individual species are stronger than the forces of interspecies mixing, then a solution CAN’T occur

2. If solute/solute and solvent/solvent interactions are GREATER than solute/solvent interactions, sometimes solutions can’t form

What kind of solid dissolves in water?

Ionic solids

Insoluble

When compounds have very very low solubility (can’t dissolve all of the solute)

Soluble

When compounds have high solubility

Solubility

amount of substance that will dissolve in a given amount of solvent

Saturated solution

A solution that has dissolved the max amount of solute possible (at a given temp) + in dynamic equilibrium with any undissolved solute

Unsaturated solution

A solution that has NOT yet reached its max amount of dissolved solute, so it can still dissolve more (it is NOT a dynamic equilibrium)

Temperature’s effect on a solid inside a liquid

As temperature INCREASES, solubility of a solid in a liquid INCREASES (directly proportional)

• because: higher temp → higher speed of molecules → IMFs easily broken

Temperature’s effect on a gas inside a liquid

As temperature INCREASES, solubility of a gas in a liquid DECREASES (inversely proportional)

• bc: IMFs are broken easily due to high T → gases are able to escape into the surrounding air

Pressure’s effect on a gas inside a liquid

As pressure INCREASES, solubility of a gas inside a liquid INCREASES (directly proportional) aka Henry’s law

• bc: increased P → gases have more forces pushing them into the liquid

Henry’s law + define formula

Sgas = kP

Sgas = solubility of a gas in a liquid

k = Henry’s law constant

P = partial pressure of the gas above the liquid

As pressure INCREASES, solubility of a gas inside a liquid INCREASES (directly proportional)

When are the rates of dissolution (dissolving) and recrystallization in a solution the same?

When a solution is in dynamic equilibrium

Dissolution

dissolving

Recrystallizaiton

Where dissolved solute particles come out of solution and form solid crystals again

Supersaturated solution

A solution that contains more dissolved solute than is normally possible at a given temperature.

In a dynamic equilibrium:

A solute is continually dissolving and precipitating AND the number of products and reactants stay the same

M = ?

1 mol/1 L

Practice: Sea water is about 600 mM of NaCl. How many grams of NaCl are in 250 mL of sea water?

Answer: Around 8.766 grams of NaCl

Colligative property

Property that depends on the number of particles dissolved in a solution rather than the type of particle

(Just list) colligative properties

1. vapor pressure lowering

2. freezing point depression

3. boiling point elevation

4. osmotic pressure

(generally) how do colligative properties change

If a substance breaks into multiple particles, it changes colligative properties

Van’t Hoff factor (i)

(i): ratio of particles in solution to formula unit

ex) NaCl (one unit) = Na+ Cl- (2 particles for every 1 formula unit)