Exam 3 Flashcards
What helps properties mix when substances do not form a solution?
Surfactants
What is an example of a surfactant?
Dish soap helping water and oil mix
What is a solute?
In a solution, a solute is the thing that gets dissolved
What is a solvent?
In a solution, the solvent is the the liquid/substance in which the solute dissolves
The interaction between solute and solvent is called… If the solvent is water it is called…
Salvation, Hydration
For something to be a true solution, it must be
A homogenous mixture
In hydration, what type of bonds typically allow ions to stay intact?
Covalent
In hydration, which type of bonds allow ions to break apart?
Ionic
When is a solution saturated?
When no more can dissolve
What happens if we add solute to a saturated solution?
It will no longer break apart and dissolve, it’ll sink to the bottom
What is equilibrium?
When two opposing forces work together at equal rates
How is a saturated solution at equilibrium?
It is a back and forth process where some things go into the solid clump and some leave
What happens to solubility as temperature increases? What is an exception?
As temperature increases, solubility increases (except for gases).
Generally, what are the rules for soluble substances?
All group 1 metals =soluble (no exceptions) Ammonium NH4+ = always soluble Nitrate NO3- = always soluble Acetate CH3COO- = always soluble Perchlorate ClO4- = always soluble Chlorate ClO3- = always soluble
Generally, what are the rules for insoluble substances?
Carbonate = insoluble (except when combined with no exception compounds
If we have a displacement reaction, how do we predict equations?
the reactants will switch partners when they become products
What is a complete ionic equation?
In this type of formula, we only write aqueous solutions as each individual ion, non aqueous solutions are written as a whole
ex: AgNO3 turns to Ag+ (aq) + NO3- (aq) BUT AgCl (s) stays intact
What is a net ionic equation?
From a complete ionic, those that changed in the reaction, get to be written. Those that stayed the same are not included and are called spectator ions.
ex: Ag+ + Cl- –> AgCl so, we would write AgCl in the net ionic
How can we describe solution concentration?
Concentration = (amount of solute)/(amount of solvent)
In a concentration problem, if we are asked for w/w or m/m, what are the units?
grams/grams
If it is v/v what are the units?
mL/mL
If it is w/v, what are the units?
g/mL
What is molarity?
moles/ liters
What is a dilution?
the process of decreasing the concentration of a solute in a solution, usually simply by mixing with more solvent like adding more water to a solution.
ex: adding more water to a salt-water solution making it less salty
In a dilution, what is constant? what changes?
In a dilution, concentration is reduced and amount of solute is constant
How can we use moles (the constant) as a conversion factor?
M1V1=M2V2
What is diffusion?
Diffusion describes the movement of particles from areas of high concentrations to low concentrations
Is diffusion faster in gases or solutions?
Diffusion is faster in gases because they are interacting with empty space. In solutions, they interact with solvent
What is osmosis?
It is a type of diffusion that has a semipermeable membrane where solvent can move (solute cannot)
Why does the solvent move in osmosis?
Water (and other solutions)have a tendency to equalize concentration on both sides of the membrane.
What is hydrostatic pressure?
This type of pressure occurs when the side with the most water creates pressure by weighing and pushing down the water.
How is osmotic pressure calculated?
osmotic pressure (π) = i (n/v) R T where i(n/v)= moles
What is the i in osmotic pressure?
It accounts for the number of particles where single elements count as one and polyatomic ions count as one.
ex: NaNO3= Na+ and NO3- i= 2
In cells, what is a hypotonic?
This occurs when there is a low concentration outside the cell so water moves in and the cell blows up
What is hypertonic?
This occurs when there is a high concentration outside of cell so water moves out of it leaving it deflated.
What must occur for a reaction to happen?
- molecules must collide with enough energy
- molecules must collide in the correct orientation
What factor would make it more likely for molecules to collide with enough energy?
heat
What is the activation energy?
the minimum quantity of energy which the reacting species must possess in order to undergo a specified reaction.
What does a forward reaction look like?
A+B -> Activated complex (spark) -> C+ D
What does a backwards reaction look like?
C+D -> Activated complex -> A + B
In a forward reaction, what is the heat energy?
Since the graph shows the products lower than the reactants, we can assume heat is being released AKA exothermic
In a backwards reaction, what is the heat energy?
Since the graph shows the products higher than the reactants, we can assume heat is being absorbed AKA endothermic.
How can we calculate the heat energy produced between 2 reactions?
We can take the difference in activation energy by subtracting the one from a forward reaction minus the Ea of a backward reaction.
What happens to reactants and products as a reaction advances?
As a reaction continues, reactants decrease and products increase.
What formulas can we use to describe the rate/relationship between reactants and products?
appearance of product/time OR
disappearance of reactant/time
What is the purpose of a catalyst?
To speed up the rate of the reaction (reaction remains unchanged but the shape (graph) of the reaction changes
What happens to the activation energy when a catalyst is applied?
It is lowered
What is a reaction intermediate?
is a short-lived, high-energy, highly reactive molecule. When generated in a chemical reaction, it will quickly convert into a more stable molecule
What is the difference between a reaction intermediate and a catalyst?
A reaction intermediate is produced early and consumed later. A catalyst is consumed early and produced later. Both are not present in the overall reaction
How do we identify intermediates and catalysts?
Reaction sequences
How do reaction sequences function?
First, look for the elements that appear either first in reactants and then in products or first in products then reactants. Once you identify them, if the element is in the reactants (first step) and products second step, it is a catalyst. If it is in the product first step and reactants second step, it is an intermediate
How is equilibrium represented?
With a double arrow
How do we find the value for constant concentration of products and reactants?
Since the concentration of products and reactants is constant at equilibrium, the value for this can be calculated by Keq = products/reactants
Only constant at a given temperature
Are all types of elements listed in Keq?
No, only gases and aqueous solutions.
What units is Keq given in?
Molarity (moles/liter)
How do we set up Keq?
As stated before, products go on top and reactants in the bottom. If an element has a coefficient, in Keq, it will be an exponent.
What does a large Keq tell us about the reaction?
In a large Keq (greater than one), we can assume that products are favored, it is a favorable reaction
What does a small Keq tell us about the reaction?
In a small Keq (less than one), we can assume that reactants are favored and it is an unfavorable reaction.
Are catalysts and intermediates included in the overall reaction?
No, we only include regular elements
How do we find Keq for reaction sequences?
Find the Keq for each individual reaction then multiply the two. Remember to cancel out the elements that are catalysts and intermediates
According to LeChatliers Principle, If we add reactant, where will the reaction shift?
Shift right
According to LeChatliers Principle, If we remove reactant, where will the reaction shift?
Shift left
According to LeChatliers Principle, If we add product, where will the reaction shift?
Shift Left
According to LeChatliers Principle, If we remove product, where will the reaction shift?
Shift right
How does heat relate to LeChatlier’s Principle?
If we have an endothermic reaction, heat is a reactant and it will shift right. If we have an exothermic reaction, heat is a product and it will shift left
According to the Bronsted Lowry definition, what is an acid?
An acid is something that donates an H+ ion AKA a proton.
How is H+ considered a proton?
Since it only has 1 pt and 0 nt, some consider it a proton
According to the Bronsted Lowry definition, what is a base?
A base is something that accepts hydrogen ions (protons).
water is an _________ species that acts as both an acid and a base
amphoteric
Why is water amphoteric?
Because water is at equilibrium with both hydroxide and Hydronium
What is the Keq (Kw) of water at 25 C?
1.00 * 10 ^-14
What are the 6 strong acids?
HCl, H2SO4, HI, HNO3, HBr, HClO4
What makes an acid strong? weak?
Complete dissociation in solution means an acid is strong. A weak acid has a partial dissociation in solution.
How can we determine if an acid is strong or weak?
By looking at the ions (products) or by calculating Keq (small Keq= Weak)
What is generally a weak acid?
Carboxyllic Acids
What bases are strong?
Generally strong bases are metal hydroxides
LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2
What are weak bases related to?
Weak bases are related to ammonia (NH3). Also, if the hydroxide is not paired with a metal, it is weak
According to the Bronsted Lowry definition, what is the relationship between acids and bases (proton donors and acceptors)?
Acids and bases come in sets AKA conjugate base pairs. Every acid-base reaction with water will result in 2 acid-base pairs. A conjugate pair is related by an H+ ion.
Ex: HCl and Cl- , H2O and H3O+
Can we write Ka and Kb values for acids and bases?
Yes the same rules apply (products over reactants) and Only include gases and aqueous solutions.
How do we tell the difference between Ka and Kb?
Ka= acid + water ⇌ H3O + conjugate base Kb= base+ water ⇌ OH- + conjugate acid
How does the K value relate to favoritism?
If we have two values with a small Ka Value, the one that is the biggest (even though they both favor reactants) is the stronger weak (acid/base).
How does the K value relate to an inverse relationship in strength of weak acids/bases?
If we determine we have a weak acid, we know the conjugate base will be strong. If we have a weak base, the conjugate acid will be strong.
How do Ka and Kb relate to Kw?
Ka * Kb = Kw where Kw = [OH-][H+] = 1.00 * 10 ^-14
What happens if we have a really small conjugate base or acid?
If we are given Ka and we solve for Kb (or vice versa) we are given a value. If Kb (or Ka) is so small we assume water is a better base/acid than Ka’s conjugate. Depending on which it is, we have an overall worthless base/acid.
How can we determine the acidic or basic properties of salts?
We can look at their cations and anions from the formula and see if what type of property we have
The conjugate of anything strong is _______
Neutral
The conjugate of anything weak is ______
Weak
Salts of small positive metals are considered _______.
Acidic
What is a polyprotic acid?
This is a term given to an acid that lose more than one proton in different steps
How do we write a formula for a polyprotic acid?
Depending on how many H+ there are, it will let us know the number of steps the reaction will take. The first step is acid + water (→ if strong Ka, if weak Ka⇄) and then using the correct arrow to write H3O + and the same ion (minus one H). Overall, you have to also make sure the charges are correct for every step.
How do we use Ka in polyprotic acids?
The larger Ka (between the steps) will determine the arrow and stronger reaction.
Single headed arrows are used for
Strong acids and bases that completely dissociate
Double headed arrows are used for
Weak acids and bases that do not dissociate
A large K value means…
Strength
A small K value means…
Weakness
Which formula do we use to calculate hydronium ion concentration or Hydroxide concentration?
Kw= [OH-][H3O+]
When calculating concentration of H3O+ or OH-, what will determine acidic or basic?
If we have a higher H3O + concentration, it is acidic. If OH- is higher, it is basic
What does the pH scale do?
It converts the exponents (from concentrations) into whole numbers
What does “P” mean? anything with P in front means….
“Take the - log of”
How do we calculate pH?
-log [H+ concentration]
How do we calculate pOH?
-log [OH- concentration]
A small pH indicates the solution is …
Acidic
A larger pH indicates the solution is…
Basic
Why does the pH scale ranges up to 14?
Because it is related to Kw
What must happen in order to have a neutral solution?
[H+] = [OH-]
What is the equation for solving pH or pOH?
pH + pOH = 14
What units is concentration in?
Molarity
Are solids included when writing equilibrium expressions?
No
What does a buffer solution do?
It resists changes in pH when a strong acid or base is added
When does a buffer work at its best?
When ph = pKa
How do we know we are solving for buffer?
If we are given a solution and its conjugate base with values
Which equation do we use for buffer solutions
Henderson Hasselbach (pH= pKa + log (base/acid)
What is the relationship between M and V?
They have an inverse relationship
To find pH, what do we do?
-log [H3O+]
To find pOH what do we do?
-log [OH-]
To find concentration of H3O+, what do we do?
10 ^-pH
To find concentration of OH-, what do we do?
10 ^-OH
To find pOH from pH or pH from pOH, what do we do?
pH+pOH = 14
Usually, Hydrogen with a nonmetal is considered a/n
acid
Usually, Hydrogen with a metal is considered a/n
base
In a formula, if H acts as a cation, it is a/n ______
acid
In a formula, if H acts as an anion, it is a/n
base
If we are mixing a strong acid in water and writing a chemical formula, what must we use?
A single arrow
is h30+ the same as H+?
yes
Since pH and pOH concentration is in Molarity, what should we do if we are given grams and ml?
If we are asked to solve for pH and pOH given g and ml, we must convert those values into M and then solve
If our titration solution is dark pink, what happened?
We have so much base that it passed the equivalence point
In titration problems, what are we essentially working with
Since a base is added to an acid, we work with the values for our base
How do we write equations for acid base titrations?
Acid + Base –> Salt + Water
make sure it is balanced
What is the general notation for finding the volume of equivalence point given molarity and initial volume?
mL to L using 1/1000 conversion
L to mol using Molarity
mol to mol using balanced equation
mol to liter using molarity and l to ml using conversion
How do we find pH of a titration?
Depending on what we are given, we make multiple conversions to find equivalence point of the base. Once we do the correct conversions, we apply that to the equivalence point. EX: if our equivalence point is 70 mL but we only have 50 mL, what does that mean for pH? It means it is not neutral, it is before equivalence pt so the solution is more acidic.
How do we find H+ or OH- concentrations?
Kw
In order to solve for hyper/hypo/iso, what should we do?
If we are given molarity, determine the number of particles (i) and multiply both. If one has a higher concentration, water will move towards it
the conjugate of anything strong is
Neutral
If we have a conjugate weak acid and base, how do we know which is the “stronger weak acid”?
Since we know the Ka values are going to be small, we simply determine which is closest to one. (inverse relationship)
