Analytical Chemistry Final- ACS Exam Questions with Complete Solutions 2024, Study Guides, Projects, Research of Chemistry

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Analytical Chemistry Final- ACS

Exam Questions with Complete

Solutions 2024

ppm (grams analyte/grams sample)x10^ Molarity moles analyte/liter of solution Volume Percent (volume solute/volume soution)x Volume ppm (volume solute/volume solution)x10^ kilo- 10^ deci- 10^- 1 centi- 10^- 2 milli- 10^- 3 micro- 10^- 6 nano- 10^- 9 pico- 10^- 12 femto- 10^- 15 weight percent

(grams analyte/grams sample)x ppt (grams analyte/grams sample)x10^ ppt simplified gram analyte/liter solution ppm simplified mg analyte/liter solution ppb simplified micrograms analyte/liter solution pptr simplified nanograms analyte/liter solution buoyancy correction m=(m'(1-(air density/weight density)))/(1-(air density/object density)) accuracy closeness of the mean to the "true value" precision reproducibility of individual measurements Uncertainty in Addition/Subraction e=sqrt(ex1^2+ex2^2+ex3^2+...) Uncertainty in Multiplication/Division e=y*sqrt((ex1/x1)^2+(ex2/x2)^2+(ex3/x3)^2+...) Significant Figures in Logarithms and antilogarithms the number of significant figures in the log should equal the number of digits in the mantissa How many significant figures in log(205.5) four significant figures, so you will need four decimal places in your answer pH

• log[H3O+] [H3O+] 10^-pH Absorbance
• log(transmittance) Random Error
• repeated measurements are sometimes high and sometimes low
• cannot be corrected for Systematic Error
• repeated measurements are usually always high or always low
• can and should be corrected for

Relative uncertainty= absolute uncertainty/magnitude of measurement 68% of measurements in a Gaussian Curve will lie between the mean-1 and the mean+ Variance in standard deviation standard deviation squared mean= true value +-time*standard deviation T-test Case 1 measure sample of known composition T-test case 2 compare replicate measurement of an unknown sample T-test case 3 compare individual difference of an unknown sample

• two sets of data analyzed by both methods being used T-test case 1 equation true value= mean (+-) (time*standard deviation)/sqrt(number of measurements)) T-test case 1 Tcalc= (sqrt(n)Iknown value-calculated meanI)/standard deviation For Case 1: If Tcalc>Ttable the actual value isn't in the range and it is bad For Case 1: If Tcalc<Ttable the actual value is close to our calculated value For Case 2: you need to first solve for Fcalc= (larger standard deviation)^2/(smaller standard deviation)^ If Fcalc<Ftable, you should use Case 2A If Fcalc>Ftable, you should use Case 2B T-Test Case 2A: Tcalc= (Icalculated mean 1-calculated mean 2I/spooled) sqrt((n1 n2)/(n1+n2)) For Case 2A: if Tcalc < Ttable, then the two sets of data are statistically indistinguishable

For Case 2A: spooled(standard deviation pooled)= sqrt((s1^2(n1-1)+s2^2(n2-1))/(n1+n2-2)) where s=standard deviation and n=number of measurements For Case 2B: Tcalc= (Icalculated mean 1-calculated mean 2I)/sqrt((s1^2/n1)+(s2^2/n2)) For case 2B: if Tcalc<Ttable, then the two sets of data are indistinguishable For Case 3: Sd= sqrt((sum of (difference-average difference)^2)/n-1) For Case 3: Tcalc= (Iaverage differenceI/Sd)*sqrt(n) Q-test Q=gap/range For the Q-test, if Qcalculated>Qtable, the value in question can be rejected with 90% confidence Grubbs test Gcalculated= Iquestionable value-calculated meanI/standard deviation

• calculated mean and standard deviation need to include the questionable point For the Grubbs test, if Gcalculated<Gtable, you need to keep the questionable point in the set of data Absorbance corrected for dilution= Absorbance measured(total volume/initial volume) Energy= Plancks constantfrequency Planck's constant= 6.626x10^-34 Js c=(in terms of energy and absorption) wavelenghtfrequency E= (planck's constantc)/wavelength Beer's Law Equation Absorbance= constant distance concentration

Transmittance Equation= P/Po Po= particular intensity at a specific wavelength Percent Transmittance= Transmittance x Acid has a conjugate base and could potentially donate a proton Base has a conjugate acid and could potentially gain another proton what k do you have when you have a base + water on the reactants side? Kb what k do you have when you have an acid + water on the reactants side? Ka what k do you have when you have a base + water on the products side? 1/Kb what k do you have when you have an acid + water on the products side? 1/Ka what is the k equation? k=products/reactants

• this does not include any solids or liquids, only aqueous solutions what is the k-value associated with the dissociation of water molecules or 2H20 ⇌ H3O+ + OH- Kw=1.0x10^- 14 Kw= [H30+][OH-] Kw= (in terms of other k values) Ka*Kb pKw= pH+pOH A weak acid consists of a Ka value of 10^-3 or less Direct Titration standardized titrant is added to the analyte until the end point is observed Indirect Titration includes a back titration, and occurs whenever a direct titration is not feasible Dilution Factors M1V1=M2V Push the reaction to the products side if you have a

very large K value Push the reaction to the reactants side if you have a very small K value You need to consider the autoprotolysis of water when the concentration is <10^- 5 How to write a charge balance equation You put all of the positive charges on the left hand side and all of the negative charges on the right hand side. You need to take the number of charges and use it as a coefficient out front. In Example: NO3^4- : 4[NO3^4-] How to write a mass balance equation Concentration of Solution= concentration of both products. If one of the products can add or lose a proton that needs to be included in the equation. *metals and chloride ions do not gain or lose any protons. Charge Balance Equations can only have one of these equations per problem Mass Balance Equations can have multiple of these equations per problem when do you use the Henderson-Hasselbalch equation? when you are dealing with buffers Henderson-Hasselbalch equation pH=pKa+log[A-]/[HA] titrant the liquid that goes in the buret and what is going down analyte unknown that you are trying to figure out equivalence point theoretical volume of titrant to completely react with the analyte end point experimental volume of titrant needed to completely react with the analyte and determined by a physical change in the solution of the analyte titration error difference between equivalence point and end point primary standard

• typically used to determine concentration of the titrant
• an ideal primary standard would have high purity(99.9%), stable, cheap, relatively high formula weight standard solution solution that has known composition zwitterionic form

an ion that can be an acid or a base How do you solve polyprotic titrations if Ka1 is 3 orders of magnitudes larger than Ka How do you solve polyprotic titrations for the zwitterionic form of the ion you use our special tool to solve for [H3O+] [H3O+] using the special tool equation: =sqrt((K1K2[HL]+K1Kw)/(K1+[HL] [H30+] simplified using the special tool equation: =sqrt(K1K2) pH using the special tool equation: =0.5(pK1+pK2) Finding the predominant species in monoprotic acids: alpha HA= [HA]/([HA]+[A-]) Finding the predominant species in monoprotic acids: alpha A-= [A-]/([HA]+[A-]) Finding the predominant species in polyprotic acids: alpha H2A= [H30+]^2/([H3O+]^2+[H3O+]K1+K1K2) Finding the predominant species in polyprotic acids: alpha HA-= [H3O+]K1/([H3O+]^2+[H3O+]K1+K1K2) Finding the predominant species in polyprotic acids: alpha A^2- K1K2/([H3O+]^2+[H3O+]K1+K1K2) Acid-Base Titration at 0 mL =-log(analyte) Finding the Equivalence point molarity of analyte mL of analyte stoichiometry/molarity of titrant Acid-Base Titration at half-way to the equivalence point solve for x and then take the - log([H3O+]) special equation: pH=pKa Acid-Base Titration at the equivalence point solve for x and then take the - log([H3O+]) Acid-Base Titration beyond the equivalence point solve for x and then take the - log([H3O+])

Acid-Base Polyprotic Titrations at half way to the equivalence point pH=pK Acid-Base Polyprotic Titrations at the equivalence point pH=1/2(pk1+pK2) Acid-Base Polyprotic titrations half way to the second equivalence point pH=pK How do you tell which endpoint is better in a polyprotic acid-base titration curve? The endpoint that has the largest change in pH What are indicators considered? a weak acid with special characteristics monodentate one lone pair on the reactant multidentate multiple lone pairs on the reactant EDTA a hexadentate ligand with six lone pairs What is the reaction stoichiometry for EDTA? 1 to 1 no matter what how is EDTA written in a stoichiometric reaction? Y^4- alpha Y4- [Y^4-]/ Cedta Kf for an EDTA reaction [MY^(n-4)]/([M^n+][Y^4-]) Kf' (alpha Y^4-)*Kf EDTA Titration at 0 mL

• log[metal] Finding the Equivalence Point for EDTA titrations [metal] volume of metal solution [EDTA] EDTA Titration half-way to the equivalence point using Kf', you solve the ice table for x and then take - log[metal] EDTA Titration at the equivalence point using Kf', you solve the ice table for x and then take - log[metal] which will be the x that you solved for. EDTA Titration past the equivalence point using Kf', you solve the ice table for x and then take - log[metal] which will be the x that you solved for What pH is it best to work at with an EDTA Titration?

basic to keep the Kf' large Why do you add auxilliary complexing agents to EDTA titrations? To stop the metal from precipitating with OH- since the metal will bind with the complexing agent. alpha m(solving for) 1/(1+B1L+B2L^2+B3L^3+...) B= value that is given L=fixed concentration of added solution Kf'' =Kf (alpha Y^4-) alpha m alpha m(to find concentration) =[metal]/Cmetal Auxilliary Complexing Titration at 0 mL use the alpha m equation for finding concentration and then take the - log[metal] Auxilliary Complexing Titration half-way to the equivalence point solve an ice table using Kf'' and then use the alpha m equation for finding concentration to solve for [metal] and then take the - log[metal] How do you solve a back titration?

1. Find the mmols of EDTA used total
2. Find the mmols of EDTA in excess
3. Take mmols total-mmols excess to find mmols of the metal used
4. Take mmols metal used/mL of sample it is in to find the [metal] solubility units g/L Molar solubility units mol/L A Ksp reaction needs to go from what to what solid to ions *there needs to be some solid present at equilibrium Why do we use Q values in Ksp reactions? to determine whether the reaction needs to move to the right or to the left in order to attain equilibrium Q>Ksp the reaction goes to the left Q<Ksp the reaction goes to the right Q=Ksp the reaction is at equilibrium To solve for Q you need to

use the K equilibrium constant equation but use the initial concentrations of the ions How to determine a molarity if 99% of part of the solution precipitated Take 0.99*[molarity of known solution] and then use that to solve an ice table where the solid starts at 0 and then goes to some Gravimetric Titration at 0 mL can't be done because you get an error while doing the math gravimetric titration before and after the equivalence point

1. need to check which way you have to go by using the Q values- will be the same for the entire titration
2. solve the ice table using the Ksp
3. use the concentrations at equilibrium to solve for the pMETAL by taking the - log[metal] What is electrode potential? how much potential energy an electron has Nernst Equation Ecell= E°-(0.059/n)*(log[red]/[ox]) Reduction equation electrons are being added to the reactants Oxidation equation electrons are being added to the products Galvanic(voltaic) cells electrons flow in the spontaneous direction (from E- to E+) Electrolytic Cell electrons flow in the non-spontaneous direction (from E+ to E-) One electron is equal to how many coulombs? 1.6x10^- 19 One mole of electrons is equal to how many coulombs? 96,500 C(1 Faraday(F)) q(charge in coulombs)= nxF

• n is the number of moles of electrons
• F is Faraday's constant (96,500 c/mole electrons) I(current)= q/s
• q is the charge in coulombs
• s is the time in seconds
• usually in units of Amperes(A) or coulombs/second Anode the half cell that electrons leave from and where oxidation occurs

Cathode the half cell that electrons flow into and where reduction occurs Ecell= E+-E- Given a voltmeter readout, how do you determine which way the electrons flow? If the readout is a positive value, then the electrons flow from left to right. If the readout is a negative value, then the electrons flow from right to left. How do you balance a half reaction equation?

1. determine the oxidation numbers for all of the numbers
2. balance the number of non H or O atoms
3. balance the number of electrons based on oxidation numbers
4. balance the number of oxygens with H2O
5. balance the number of hydrogen with H+
6. Check charge balance and atom balance In order to have a complete half cell reaction, you must have no electrons in the final equation How do you find the K value in half-cell reactions K=10^((n*(E+-E-))/0.059) The half cell with the higher Eo tends to be a reduction equation The half cell with the lower Eo tends to be an oxidation equation The best reducing agents have lower Eo values The best oxidation agents have higher Eo values Reference Electrodes maintain constant potential(V) so that we are able to determine the potential of a different electrode What are three examples of reference electrodes? Standard Hydrogen Electrode (SHE) Silver-Silver Chloride Electrode Saturated Calomel Electrode (SCE) What is the E of the Standard Hydrogen Electrode? 0 V What is the E of the Silver-Silver Chloride Electrode? 0.197 V What is the E of the Saturated Calomel Electrode?

0.242 V

What are indicator electrodes? the electrodes that are used in the cell that are responsive to changes in analyte concentration What is a first order indicator electrode? the ion that you are looking for is the same as the metal put in the solution What is a second order indicator electrode? the ion that you are looking for is not the same as the metal put into the solution Liquid Junction Potentials uses a salt bridge to keep both half cells from having a charged potential Liquid Junction Potential in the Anode Half Cell you start with a neutral solution but when current flows out there is a build-up of positive charge in the solution Liquid Junction Potential in the Cathode Half Cell you start with a neutral solution but when current flows in there is a build-up of negative charge in the solution Liquid Junction Potential problems the migration of ions to keep the half cells neutral varies greatly causing there to be an unknown potential between the two solutions Liquid Junction Potential Ecell= E+-E-+Ejunction Ejunction= (0.059/z1)*log(Aitest/Aireference)

• z1 is the charge on the species that can cross the barrier
• Ai s the activity(molarity) of the species that can cross the barrier What else can we use to keep the complete half cell reaction neutral? a semi-permeable membrane What is one problem with the semi-permeable membranes? it cannot be made to be 0% permeable to other cations or anions A good semi-permeable membrane will have what type of K? the K value will be very very small What type of agent is used more in redox titrations as a titrant? an oxidizing agent What is the problem with using permanganate as a titrant in redox titrations? it is not a primary standard When doing a redox titration, are you able to find a point at 0 mL? no, you cannot find a point because you don't truly know the [metal] Doing a redox titration:

1. Find the K value using the equation to find K with half-cells
2. Find the equivalence point(same as with acid base titrations)
3. solve the ice tables (WATCH OUT FOR STOICHIOMETRY)
4. Solve for E+ using the concentrations you got
5. Find Ecell by taking the E+ you found- E- of the reference electrode chelate effect the ability of multidentate ligands to form more stable metal complexes than those formed by similar monodentate ligands masking agent a reagent that protects some component of the analyte from reaction with the EDTA common ion effect a salt will be less soluble if one of its constituent ions is already present in the solution Gravimetric factor (grams of substance in analyte)/(grams of product formed) what is an extraction? combine two immiscible phases (polar, non-polar), agitate, and let the analyte partition what is chromatography? combine two immiscible phases (polar, non-polar), let analyte partition what is the difference between an extraction and chromatography? one of the phases is flowing in chromatography while the other phase is stationary what is the principle of extraction? like dissolves like Ka equation for chromatography [A]stationary phase/[A]moblie phase In chromatography you want to have Ka and Kb not equal to each other Retention Factor Equation k=(tR-tM)/tM tR is the distance between the peaks tM is the distance from 0 to the first peak Relative Retention alpha=k2/k1 or alpha=t'2/t' *the smallest it can be is 1 which is bad to get Resolution(Efficiency) R=(tR1-tR2)/(0.5(w2+w1)) R must be greater than or equal to 0 Liquid Chromatography

used for samples that are not volatile, like dissolves like Normal Phase in Liquid Chromatography a more polar stationary phase and less polar mobile phase and is not used as often Reverse Phase in Liquid Chromatography a less polar stationary phase and more polar mobile phase and is used more often Gas Chromatography mostly used for gases or volatile liquids How does gas chromatography work? you use a carrier gas to "push" the analyte through the mobile phase what is a carrier gas? a non-polar, chemically inert gases, usually a noble gas