Chem II unit 2

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what is the key to solving titration problems

* if just given a random volume then determine if it is before after or at equivalence and then determine what will be present at that point on the titration chart * from there you can write the equation, then find the concentrations of species that you need according to your equation * initial, and at equivalence point use RICE- since weak acid or salt present * before equivalence uses Bdelta A and RICE- since need to see how much weak we have first * after just uses concentration since all weak components are gone * 1/2 way point just uses pka of the weak acid

How do you find pH after the equivalence point

* pH will be dominated by excess base or acid added depending on what is being titrated * Take the volume from that point and subtract from the volume at equivalence point * that left over mL is the amount of base or acid added * multiply that by the molarity of the titrant to get the moles at that point * divide that moles by the total volume that is now there (original we started with before titration + the amount of titrant that was added) * -log of that concentration = pH or pOH

How do you find pH at halfway point

* pH= pka so can just use -log of the Ka of the acid given * if graphing this, the volume is equal to 1/2 of the volume at equivalence

how would you find the pH of a titration given a random volume

* start by finding the equivalence point so you know if the volume is before or after equivalence * if the volume given is less than the equivalence point volume you write your equation with the acid and base reacting, use Bdelta A table to find number of moles of the acid and base- titrant found by multiplying molarity x volume given and the other one is given in the problem, subtract the lesser one to then be able to make a RICE chart with the weak acid reacting with water , be sure to convert back to concentration using total volume * if volume is larger than equivalence point- then subtract the equivalence point volume from that * find the number of moles in that amount of excess titrant * then find concentration by dividing by TOTAL volume * then do -log of that concentration * the titrant is strong acid or strong base so no RICE chart is needed

How do you calculate the pH at the equivalence point

* write out the equation for acid + base to see what salt you have *then take that salt that is the component that would contribute to pH and write it out in its own equation with the water to make conjugate acid or base and OH or H * write that equation out with a RICE chart * find concentration of that salt ion- by using same moles as added from titration ( M x volume of titrant to find moles) divided by the TOTAL volume in the solution (initital volume you started with + the volume of titrant added- may have to find volume of titrant added which you do by seeing how many moles you need and then how many mL of that solution you need to get that moles * Make sure to then use correct Ka or Kb according to the equation * find H+ or OH concentration and thus the pH

how do you find pH before the equivalence point

* write out your equation of titrant reacting with the weak acid or base * find moles in the volume, by multiplying the M x volume to get moles * USE BdeltaA table * write out initial moles of each species in the equation- amount of moles of weak acid/base to start with and the moles of the titrant we calculated from our given volume and molarity * subtract the lesser one * NOW make a RICE chart with the leftover weak acid or base and write out that equation -remember to convert from MOLES to molarity- DIVIDE by TOTAL volume * use Ka of the weak acid and solve for x from the RICE CHART * find pH from x concentration

Delta G standard for cell

-nFEcell, n is number of moles of electrons transferred, F is faradays constant (96,485 j/mole) (Volts (j/C)

steps to solving buffer action equation

1. write equation by identifying if a base or acid is added to the buffer and then if the acid or base in the buffer will react 2. convert any concentrations you have to moles so that anything on the Bdelta A chart is in moles 3. identify the limiting reactant and whichever one is limiting subtract that concentration from both species on the left and add it to the species on the right 4. see if you have OH or H left after, convert that in moles back to molarity then use the pH equation or pOH equation to solve for pH, if no OH or H left over do a rice chart- REMEMBER to convert back to molarity FOR THE RICE CHART- use the species that is produced, if it is an acid remember it will produce H3O + and its conjugate base and a base will produce H2O and its conjugate acid

what plot gives straight line for 2nd order reaction

1/[A] vs. t

ex: Calculate the mass of Au that can be plated in 25 minutes using 5.5 A for the half reaction Au3+ + 3 e- makes Au(s)

25min x60s/1 min x 5.5 C/s, x 1 mol e/ 96,485 C x 1mol Au/3 mole e- x molar mass of Au

what is the frequency factor

A- stands for the frequency of collisions between reactant molecules at a standard condition

Units of A and V

Amps are equal to 1 C/s and Volts are equal to 1 J/C

are q and W state function

NO

what plot gives straight line for 0 order reaction

[A] vs. t

If the pKa of HCHO2 is 3.74 and the pH of an HCHO2/NaCHO2 solution is 3.89, which of the following is TRUE?

[HCHO2] < [NaCHO2] because 3.89 is higher than 3.74 there will be more of the basic form present, so since NaCHO2 is acting as the base and HCHO2 is the acid, the basic component concentration will be higher than the acidic component concentration

common ion effect

adding a salt NaA (where A- is the common ion) shifts the position of the equilibrium to the left which lowers the H3O+ ion concentration causing the pH to be higher than the pH of the acid solution alone

common ion and solubility

addition of a soluble salt that contains one of the ions of the insoluble salt decreases the solubility of that insoluble salt

electrolytic cell

an electrochemical cell used to cause a chemical change through the application of electrical energy, forces current in NONSPONTANEOUS direction

line notation

anode is on the left and cathode is on the right side, double verticle lines separate the anode and cathode, single line on each side to show separation between starting element and the product, and include phases

what all can be used to make buffers

aside from using the weak acid or weak base with its conjugate salt, you can also use a weak acid and strong base, with that strong base usually being half the concentration- because it will create a salt and the conjugate base of the weak acid

average rate

asked to find the average rate of something over a certain number of seconds- then do the general reaction equation 1/ coefficient (conc A at time 2- conc A time 1)divided by time 2 - time 1, then when writing out the answer define the span of time used to define that rate so 0-100 seconds

how can you predict the pH of a solution that is at the equivalence point

based on the nature of the salt that is present- if it is a conjugate base of weak acid it is basic if it is conjugate acid of weak base it is acidic if it is anything else then it is neutral

buffer action vs. buffer solution problem

buffer action is just the added acid or base and whichever species it is reacting with with a single arrow, and a base reacting with acid makes water, a buffer solution has both parts of buffer with water and a double arrow

what is cathode vs anode

cathode is positive end where reduction occurs, anode is negative end where oxidation occurs

how do you choose the components you want for your buffer system

choose a weak acid with pKa= to desired pH

how do we determine if precipitation will occur

compare Q for the current solution concentrations to the value of Ksp

relationship between delta E and q

delta E= q at constant volume,

relationship between enthalpy of system and q at constant pressure

delta H= q at constant pressure

how do you write the reaction for a buffer reaction

determine if the species added is a strong acid or a strong base, then react with with the opposite thing in the buffer, for example if NaOH is added that is the strong base so the reaction will be OH- + the acid that is present in the buffer (single arrow) conjugate base and H2O

differential rate law vs. integrated rate law

differential rate law is rate vs. concentration integrated rate law= concentration vs. time data

what is endpoint and equivalence point

end point is when there is a color change with the indicator, the equivalence point is when the reaction is complete and all the acid or base has been neutralized- they are not the same but hopefully would happen at the same time

writing balanced equation for a cell given two reduction equation

find which one should be flipped in order to make most positive, then write that equation flipped, then add the two equations together and balance them so that the number of e- transferred matches, given the concentrations of each of the components can calculate the cell at nonstandard conditions using E=Ecell- .0592/n (log (q) where Q is products/reactants concentrations make sure to include exponents

units for k

for 0 order= m/s, first order is 1/s, second order is 1/(mxs)

how do we draw a voltaic cell

given 2 reactions to be used in it and the standard reduction potentials, use the standard reduction potentials to decide which one can be flipped in order to add them to make a positive E, then look at which one is the oxidation reaction and which one is the reduction, then the anode is oxidation, reduction is at cathode, and then the flow of electrons- always move from anode to cathode, in the salt bridge, show the positive ions arrow towards the cathode, the negative ions in the salt bridge towards the anode

heterogeneous vs. homogeneous catalysts

homogeneous catalysts are in the same phase as the reactant, heterogeneous catalysts are in a different phase than the reactant

what is kinetics

how fast a reaction occurs in time, NOT if it is spontaneous or not

how do you know what equation to use to find the pH of a buffer

identify the weak acid, the conjugate base that is in the salt, and just use the weak acid + H2O (arrow ) conjugate base as the anion + H3O +

how to predict if a metal will dissolve in an acid

if the acid can OXIDIZE THE METAL so the reduction of the H+ is more positive than the reduction of the metal ion- look at the reduction of both of them from the standard reduction table and see which is more positive, so you would have the reduction of H+ and the oxidation of the metal, from neutral metal to positive metal cation

how to know if you should use integrated rate law or general rate law

if the question gives concentrations of reactants and a rate then use general rate law, if it asks for the average rate law from concentrations and times given then just use the general one, if it gives you half life and asks to find k or gives k and asks to find concentration then use integrated rate law

how do we know if reaction mechanism is possible

if the rate law of the slowest step matches the experimental rate law then the mechanism can be true

le chateliers principle with galvanic cells

if the reactant concentration is increased past standard conditions the voltage will increase, if the product concentration is increased past standard conditions then the voltage will decrease

how can you determine the form a compound will be in based on the solution it is in

if the solution is more basic than its pka it will be in basic form, if the solution is more acidic than the pka it will be in its acidic form

what happens to entropy in any spontaneous reaction

in any spontaneous reaction the entropy of the universe increases so delta S is positive

calculate standard cell potential

it is the reduction potentials from the chart, one flipped, add together to get standard reduction potential

what happens if base is added to a buffer

it reacts with the HA and the reaction goes forward to make more A- and water

what happens if acid is added to a buffer

it will react with the A- to produce more HA

if the pKa of phenolphthalein is 9 then what color would the indicator be at pH 3

it would be clear since it is in its acidic form below pH 8. If it was above pH 10 it would be dark pink since that is its basic form and if it is between 8.1-9.9 it would be the mix of clear and dark pink which is light pink

what happens if you add and acid to solution with M2 and OH

it would increase the solubility because the H+ ions would react with the OH and the solution would move to the right to fill in for the lost OH ions

how do we find the volume of titrant added at equivalence point

know amount of moles in the weak acid or weak base, so then using molarity of the titrant and those moles find the volume of titrant needed to have that number of moles in it

what plot gives straight line for first order reaction

ln[A] vs. t

when calculating E that is not at standard temperature what is important to pay attention to in the reactions

make sure the number of electrons are the same in each half reaction, and multiply the same number as you do to the electrons to the entire equation

electroplating questions

make sure to always convert time to seconds, since A is C/second, C from Faradays constant will be on the bottom, and then balance mol of the element with the number of moles of electrons per mole of the element

what is entropy

measure of disorder, so increases as the number of arrangements that are available to a system increases

pka

measure of protein binding affinity

what affects reaction rate

nature of the reactants- gas-liquids-solids concentration of the reactants- higher concentration increases the frequency of collisions between reactant particles, higher pressure of gases increases concentration temperature- higher temp presence of catalyst- affect speed of reaction without being consumed

does first order half life depend on concentration

no

can you compare Ksp values

no, unlike Ka values you cannot compare Ksp values, unless the number of ions is equal

catalyst

not used up in the reaction, appears as a reactant and THEN as a product too

precipitation

occurs when concentration of the ions exceed the solubility of the ionic compound

anode and cathode in electrolytic cell

oxidation at anode and reduction at cathode- but + terminal is the anode and - terminal is the cathode, electrons are forced toward the cathode

Henderson-Hasselbalch equation

pH = pKa + log [A-]/[HA], only use for buffer solutions

what is the effective pH range of a buffer

pKa +/- 1

how do you find pka

pKa=-logKa

how to slow corrosion of metals

paint, sacrificial anode that is a metal that is more reactive and will be oxidized firstghhhh

how to solve what is the minimum [OH] necessary to begin precipitation of Mg2+ with [.059] with seawater

precipitating occurs when Q=Ksp, so Q=[Mg][OH], look up value for Ksp and just solve for OH

reaction mechanism

proposed series of elementary steps that add up to overall equation

how do you write the equation for just a buffer solution

put the acid on the left + H2O and the conjugate base on the right side + H3O +

general rate law equation

rate law= k[A]^y [B]^x, where x and y are determined experimentally and ARE NOT the coefficients, if A is one then if the reaction rate doubles A concentration doubles

what is the arrhenius equation used for

relationship between temperature and rate constant, k

what do you need to remember for RICE chart after the Bdelta A chart

remember to convert moles to MOLARITY- need to include the total amount of liquid so add the mLs together, also remember to pay attention to the equation, if it is an acid that is produced then in the RICE chart that is the starting species and it produces conjugate base and H3O +

which order has slope= to + k unlike the others

second order

what is the plot of lnk vs. 1/T

slope is -Ea/R

Ksp

solubility product constant

Q>Ksp

solution is above saturation, salt above will precipitation

Q=Ksp

solution is saturated, so no precipitation

Q<Ksp

solution is unsaturated, no precipitation

what are most buffers made of

solution of weak acid with solution of soluble salt containing the conjugate base anion- so basically a weak acid + its conjugate base in the form of a salt

what are buffers

solutions that resist changes in pH when acid or base is added by neutralizing the added acid or base

How do you solve a problem, how many grams of hydroxyapatite will dissolve in 1L of H2O, given molar mass and Ksp

solve for the Molar solubility using Ksp and the coefficients with S, then multiply the value of S by molar mass to find grams, since S is the amount of moles that dissolve

what is an intermediate in a reaction

species that is formed and consumed in the steps so it is not in the overall reaction- first is a product and then is a reactant

how do you solve for the units for k for any general reaction

start with k being m/s in 0 order then figure out what k would be with addition of new concentrations with those coefficients

Faraday's law

the amount of metal deposited during electrolysis is directly proportional to the charge on the cation, the current, and the length of time the cell runs

first law of thermodynamics

the energy of the universe is constant, delta E is 0

third law of thermodynamics

the entropy of a perfect crystal at 0K is 0, s is 0 when T=0

what are the exponents in the rate law when doing reaction mechanisms

the exponents are equal to the coefficients in front of the species in the equation

how do you know what reaction will happen in an electrolytic cell

the half reaction that leads to the most positive or least negative E cell will be the one that occurs EXCEPT- Cl- oxidizes to Cl2 before water oxidizes to O2

half reactions

the individual reduction or oxidation reactions that are combined in the overall reaction

what is true about moles at the equivalence point

the number of moles added from the known is equal to the number of moles of the acid or base that was present in the solution

molar solubility

the number of moles of solute that will dissolve in a liter of solution

what is pKa

the pH where the concentrations of A- and HA- are equal

what can we tell from the halfway point on a titration curve

the pH- and we know the halfway point from the equivalence point- if the equivalence point is at 10mL then the halfway point is at 5 mL

what does it mean delta E is a state function

the path does not affect the outcome, there are not 2 states that would affect the change in E

instantaneous rate- how to find

the rate at one instant in time using concentration vs time plot, use slop of the line tangent to the curve at that time, so if you want to find instantaneous rate at 100 s then draw a straight line that only intersects 100 seconds and find the slope of that line- substitute into the rate equation and then do 1/the coefficient

what is comparative rates

the rate of one species relative to another, depends on the coefficients in that equation and which side of the arrow it is on

what happens when you change the concentration of a species at equilibrium

the reaction will shift but the K remains the same

Ksp expression

the same as K expression but we do not include solids in our expressions so it will just be the products, and remember to raise them to the power of their coefficients

what is the rate determining step

the slowest step

which step has the largest activation energy

the slowest step

how do the buffers work

the weak acid reacts with added acid and the conjugate base reacts with added acid- eventually the necessary component of the buffer will run out and the solution pH will change significantly, this works by le chateliers principle- if you add H+ to the system it will react with the conjugate base to make HA and keep the concentration of H3O constant

electroplating

the work piece is the cathode, cations are reduced at the cathode and plate to the surface of the work piece

what concentrations are true when pH < pKa

there is a higher concentration in the acidic form

what concentrations are true when pH> pKa

there is a higher concentration of basic form

what must happen for collisions to be effective

they must occur with proper orientation and sufficient energy

where do the salt bridge anions move

toward the anode, since oxidation occurs here the + charge builds up as electrons leave resulting in the anions being attracted to it

where do salt bridge cations move

toward the cathode

how do you calculate initial pH on a titration curve

use a RICE chart to find the pH initially because it is just the pH of the weak acid or the weak base

how do you calculate what ratio of NaCHO2:HCHO2 would be required to make buffer with pH of 4.25

use equation pH=pKa + log([A-]/[HA] , the ratio equals 3.24 so need 3.24 as many moles of CHO2 as HCHO2

what species exist at the equivalence point

water and a salt - NO acid or base

how do we select an indicator

we find the pH at which our solution has the equivalence point, and then find the indicator with the pKa equal to that pH

what are indicators generally made of

weak acid

what characteristics allow a buffer to have largest capacity

when HA- to A- ratio is 1 and have a reasonable molarity

how can you predict the color of indicators

when there is 50/50 of the acid and base components of the indicator the pH that will give you that mix is equal to the pka of the indicator and that is where there will be a color change- the acidic form of the indicator is one color, the basic form is another color, and where there is 50/50 acid and base it is the mixed color of the two

how to write a chart for electrolysis

write down all the possible reactive species given your element (for ex: given MgI2, then you have Mg2+ and I-, and also H2O since it is (aq) write down the possible reactions that could occur- if a reduction could occur or an oxidation- look at the chart and see what half reactions you can find with the species you are looking for, then choose the redox rxn with the most positive reduction potential and the oxidation rxn with the most positive oxidation potential, then using the 2 you selected write the combined equation

how do you calculate the molar solubility of lead (II) chloride in water given Ksp

write expression (always the solid on the left), write out a RICE chart with the initial amounts of both species on the right being 0, then +S for both, but use +2S when the coefficient is greater than 1, fill in the expression using the S terms and set equal to Ksp and solve for S, the value of S is the molar solubility

How do you find the Ksp of Lead (II) bromide if its molar solubility in water is given

write out the equation and RICE chart, start with 0 again as initial amounts, then fill in the change column with the value for the molar solubility- remember to multiply the value by the coefficients, then Ksp is equal to those values as you multiply them out according to Ksp expression

how do you calculate the molar solubility of calcium fluoride in .1M sodium fluoride

write out the expression like normal with RICE chart, in the initial column however, write down the molarity of what is already present, so F- ions will already be present at .1M, then add S and 2S accordingly since there is a coefficient, and F- will be .1 + 2S, write out the Ksp using your values, S= the molar solubility

how do you calculate the rate law experimentally

write the rate law out with variables so that you can enter in values from experimental data, choose two sets of data where only one of the concentrations of reactants changes, solve for one of the exponent variables, then use another set of experiments plug into that and solve for y

does 0 order half life depend on concentration

yes

does second order half life depend on concentration

yes

what happens in a reaction where the concentrations of 2 of the reactants is much larger than the third reactant

you can write a new rate law that is k'[concentration of lowest reactant A] to find k then k'=k[reactant B][reactant C] solve for k using k' and the reactants of B and C to solve for the actual rate constant k

how do you calculate the pH before the equivalence point

you need to know the volume at equivalence point


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