Shit You Struggle With

Question 1

What is the rate constant and what are its relationships to temp and E(a)?

Is k affected by concentration?

Answer 1

k :
Is proportional to the probability that a collision will result in a successful rxn.

It is not affected by the concentration of the reactants. It is completely independent of concentration- because it is a constant, it gives you probability regardless of how many molecules you have.

Specific relationships:
1)) is indirectly proportional to the E(a)

2) is directly proportional to temperature

Question 2

What is M (molarity)?

Answer 2

Mols solute / L sol’n

Question 3

What is Molality?

Answer 3

Mol solute/ kg solvent

Question 4

How are molarity and molality related in aqueous solutions?

Answer 4

They are not close when the amount of solute added to solution increases (concentrated solutions). Molality’s measurement will always be larger in these cases.

For dilute solutions, they are very close to the same value.

Question 5

What is a mole fraction?

Answer 5

Mols of whatever you’re interested out of the total amount of moles
Present.

“Chi”=Moles (x)/total moles

Question 6

What are the solubility rules for the MCAT that you need to know?

Answer 6

1) ALL group 1, NH4+, NO3-, ClO4-, C2H3O2- compounds are soluble

(If you see these in an ionic compound, it’s soluble in h2o)

2) MOST silver, lead, mercury (2+ ; aka “mercury 1”), these are usually insoluble in H2O

AgCl —> no. AgNO3 —-> yes!

Phases:

1) most solids are more soluble at high temperatures.

2) gases are less soluble at high temperatures.
Bubbles before water boils

3) gases are more soluble at high pressures

Question 7

Colligative properties are what:

Answer 7

Properties about a soln that change as you add more solute.

Ex: H2O alone doesn’t conduct electricity, but when infused with electrolytes it is highly conductive.

Soln properties change with increasing solute concentration.

1) Freezing point depression - inconsistent shapes disrupt the lattice (crystal) structure of the solvent. You have to cool the liquid more to make the molecules lattice up. For mcat purposes, it doesn’t matter what the solid is, but it does matter how many molecules of that solute you have.
2) boiling point elevation
3) vapor pressure depression
4) osmotic pressure

Question 8

Describe Freezing point depression

Answer 8

Freezing point depression is based on the idea that the greater the molality of your solute concentration the greater the freezing point depression of the soln. This is really only ideal gases only, but that’s all that’s on the MCAT. So for now this is absolute. The identity of the solute doesn’t matter, but how much of it, does.

This colligative property is based on:

🔼T(freezing)= -i (k(freezing))m

Where k is the freezing point constant in degrees C/molal, m= molality of soln, and i is how many pieces something breaks into - this is the Van Hoff factor, (i). i is negative because T(freezing) is going down.

The product of i and molality (m) gives you the overall concentration of dissolved solute particles solution

Question 9

Describe boiling point elevation

Answer 9

🔼Tboil= i (kb) m

The more solute you add the more energy you have to add to your solution to get it to boil.

You may have been taught that it’s because of greater inter-molecular forces, but in fact, it is because addition of solutes increases the free energy of a solution. When it has more free energy, you have to add energy into it to bring it back to the place where it’s free energy is gone, in order to force it to phase change.

Question 10

What is unique about k(f) or k(b) in terms of colligative properties and what do they tell you about the solution? What is the kb &kf or H2O?

Answer 10

Each solution has its own unique kb or kf.

H2O has a kf=1.86 C/molal
Kb= 0.51 C/molal

What these constants tell you is the depression of the FP or elevation of the BP per every molal you add into soln.

Example: If you add 2 molals of solute into water, the FP will depress by 2*1.86C/molal Remember identity of solute doesn’t matter for colligative properties.

Question 11

Describe vapor pressure depression and Raoults Law:

Answer 11

Partial pressure H2O= chi(H2O)(P of pure H2O)

Is raoults law ^, where chi is the mole fraction of the compound of interest.

Vapor pressure depresses (changes) with the partial pressure of something in gaseous form. Gases are in equilibrium with the liquid they are in contact with.

For example, if you wanted to know the vapor pressure depression of water of a 10molal soln containing 1 mol of C2H6O, you would do :

(9/10)*20torr = 18 torr, or the new vapor pressure of h20 in this situation.

Here the molal concentration of h20 in solution is 9/10 mols, the other mol is the organic compound. Pure h20 has a vapor pressure of 20 torr. So it’s the mol fraction in sol’n times the pure vapor pressure of the compound of interest, to find the vapor pressure depression for that same compound.

Question 12

What is osmotic pressure?

Answer 12

PV=nRT

P=(n/v)RT n/v is moles of gas over volume, or molarity

So,

P=MRT

We’re talking about dissolved species in H2O now, so osmotic pressure, pi and remember can hoff factor to ultimately yield:

pi= iMRT.

Question 13

Catalysts do what and how many types are there?

Answer 13

Catalysts lower the Ea of the rxn. They only help you reach equilibrium faster, requiring much less energy. Otherwise, nothing else. They do nothing else.

They do affect forward and backward rates.
There are two types- Hetero and homo. This refers to the phase the catalyst is in, when compared with the reaction. If the catalyst is in phase with the rxn, it’s homo. If it’s out of phase its hetero.

For example: a gaseous rxn proceeds in the presence of a solid platinum catalyst. Pt in this case is a heterogeneous catalyst.

Question 14

Equilibrium is most simply defined as:

Answer 14

Rate fwd = Rate rev

Question 15

At equilibrium? What is true about the reaction?

Answer 15

At equilibrium, the concentrations of the reactants and the products are not changing. They are still being created and destroyed, just the rates are equal so the concentrations can be considered constant.

Question 16

What is Kc or KP?

Answer 16

Equilibrium constant capital K-

using Kc, you’re using molarity to determine concentration (aq species)

KP- means you’re using partial pressure to measure concentration

Gases can use either one

Question 17

What expression is associated with the equilibrium constant K?

Answer 17

Kc= [products]/[reactants]

Usually Kc will include gases and aqueous stuff

KP=partial pressure products/partial pressure of reactants

For mcat purposes both of these are Keq also.

Question 18

What’s an elementary rxn? What does this tell me about rate law?

Answer 18

Can’t be broken further. Coefficients are the orders.

Question 19

What can be said about the rxn under the following conditions:

Kc»»1
Kc«<1
Kc~1

Answer 19

At equilibrium, rxn favors products

At equilibrium, rxn favors reactants

At equilibrium, you’ll have both present

Question 20

How does rate law link to equilibrium?

Answer 20

Rate forward/rate reverse =Equilibrium constant, Kc

Question 21

What unit is concentration in when presented like This? [O2]

Answer 21

Molar concentration (molarity)

Question 22

The ratio between products and reactants is always equal to?

Answer 22

Q

Question 23

Is Q always = to Kc? Why or why not?

Answer 23

No. Q can be measured not at equilibrium and still give a true ratio. Kc is only = Q at equilibrium

Question 24

What is happening to the rxn under the following conditions?

K> Q
K

Answer 24

Q is too small, so the rxn shifts right, more reactants need to turn into products.

Q is too big, rxn shifts left: more products need to turn into reactants.

K=Q at equilibrium

Question 25

Le chatliers principle says what

Answer 25

If you put a stress on the system at equilibrium, the system will respond to try and counteract the stress

Question 26

For a system at equilibrium, does the addition of solids and liquids constitute a stress?

Answer 26

No. The addition of solids and liquids does not constitute a stress that results in an eq reaction shift. If you add more solid to a rxn at eq, nothing will change. This is not a stress the system will respond to.

Question 27

What factor can change the equilibrium constant?

Answer 27

Temperature

Question 28

If you add or subtract product or reactant, is it valid to say you have changed the equilibrium constant, based on :

Kc = [Products]/[Reactants]

?

Answer 28

No! You’ve changed Q! Kc is only affected numerically by Temperature

Question 29

What tricks can come at you with shifting equilibrium?

Answer 29

Ones that cause a shift:

1. Adding more reactants or products (affects Q)
2. Changing pressure with changing volume (affects Q)
3. Changing temperature (affects Kc)

Ones that do not cause a shift:

1. Adding a solids or liquids
2. Adding inert gases (pressure changes but molarity: moles of solute/L of solvent does NOT)

When checking to see if Q or Kc is affected, look at molarity. If your mols per L are unchanged by the new condition, you’ve not affected Kc or Q.

Question 30

Can shifting the equilibrium maximize the amount of solid present? Can adding solid affect Equilibrium?

Answer 30

If the solid is part of the rxn, you can maximize amount of solid present by shifting equilibrium.

However you CANNOT affect equilibrium (cause a shift) by adding a solid. I don’t know why.

Question 31

At what voltage do the sodium voltage gated channels open and in what direction do the Na+ ions flow?

Answer 31

-50mV and into the cell

Question 32

When do voltage gates K+ channels open?

Answer 32

The apex of depolarization, about -35mV.

Question 33

When do voltage gates K+ channels close?

Answer 33

-90 mikivoltz, or hyper polarization.

Question 34

What re-establishes testing membrane potential after an action potential?

Answer 34

Na+/K+ pump

Question 35

What is the refractory period? Can you cause an action potential during this time?

Answer 35

The time it takes for the sodium voltage gates channels to reset. For neurons it’s roughly 1-mili-seconds

Yes but it is more difficult. This is the period during hyperpolarization, so you would need a much greater stimulus to get the AP to fire again.

Question 36

When we say “greater stimulus”, what does that actually constitute/how can you affect it?

Answer 36

1) increase the amount of neurons firing

2) increase the frequency of stimulus (same small amount of neurons firing more rapidly)

Question 37

What ion is concentrated inside the neuron? What ion is concentrated outside? Which what do they love during AP?

Answer 37

k+ - circle K -> moves out at apex of depolarization

Na+ outside —-> rushes into the cell when cell stimulus hits threshold (-50mV)

Question 38

What kind of impulse is the AP? Electrical, light, or otherwise?

Answer 38

It is chemical

Question 39

When do Ca2+ voltage gated ion channels open and where are they?

Answer 39

Action potential reaches synaptic knobs in the presynaptic neuron. Voltage gated Ca2+ channels open. Ca2+ is outside the cell. Ca2+ is the uptaken into the cell. Ca2+ binds intracellularly to signal release of vesicles that exocytose the neurotransmitter into the synaptic cleft.

Question 40

When the neuro transmitter binds in the synaptic cleft to the post synaptic cell, what is the main thing that happens as a result? What happens to the neurotransmitters?

Answer 40

Ion channels open that could make the cell more positive or negative.

If they make the cell more negative, these are inhibitory post synaptic potentials

If they make the cell more positive, these are excitatory post synaptic signals. (If -50mV is hit, the AP continues)

Neurotransmitter activity is terminated: diffuses away, degraded, or re-uptake into the cell for future use

Question 41

Ion channels stimulated by neurotransmitters can be categorized into two kinds of signals, based on the ions they release into the post synaptic neuron:

Answer 41

Inhibitory (-)

Excitatory (+)

Question 42

What degrades neurotransmitter acetylcholine?

Answer 42

Acetylcholinesterase —> choline and acetyl co-A; re-uptake, cell makes more acetylcholine from these blocks

Question 43

What does G protein response lead to

Answer 43

Second messenger system, not the receptors themselves.

Question 44

Where does biosynthesis take place in the neuron?

Answer 44

The cell body

Question 45

In fatigue, what is happening?

Answer 45

Pre-synaptic cell is running out of neurotransmitter and cannot make more in time to keep up with reproducing the stimulus.

Question 46

Hyperopia is ? And is corrected with what kind of lens?

Answer 46

Farsightedness- Image is focused behind the retina. Corrected with convergent lens.

Question 47

Myopia is? And is corrected with what type of lens?

Answer 47

Nearsighted ness - Image is focused infront of the retina. Corrected with divergent lens.

Question 48

Where are proteins vs steroids made?

Answer 48

Rough Er vs smooth ER

Question 49

Steroid hormone receptors are typically where? Peptide hormone receptors are typically where?

Answer 49

Steroid: inside the cell because they can passively diffuse across the membrane. Binding to receptor usually regulates transcription in some way.

Protein: outside the cell because they cannot permeate the membrane. Second messenger systems are used to transmit the signal inside the cell.

Question 50

Tropic hormones are:

Answer 50

Hormones that controls other hormones (adrenocorticotropic hormone)

Question 51

What is a solubility product constant?

Answer 51

An equilibrium constant (Ksp) that deals with a very specific type of reaction. In this case, the reactant is usually a solid or a liquid and is therefore by included in the rate law. Ksp is assigned to rxn a like this and is known as the solubility product constant, because it only describes concentrations of products (the reactants were solid and not included in the rate law).

Question 52

Ksp stands for what

Answer 52

The equilibrium constant when an ionic solid dissociates into its ions.

“Solubility Product Constant” or “Solubility Product”

Question 53

What is x from an ice chart?

Answer 53

The molar solubility.

Question 54

For rate law, how is order determined?

Answer 54

Rxn order (exponents) must be determined experimentally.