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Analytical Chemistry Test Questions

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Molarity (M)
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mol / L total solution
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Molality (m)
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mol solute / kg solvent
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weight %
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(mass analyte / total mass) x 100
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ppm
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mg / L

(mass analyte / mass tot soln) x 10^6

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ppb
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(mass analyte / mass tot soln) x 10^9
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ppt
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g / L

(mass analyte / mass tot soln) x 10^3

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Schlieren Effect
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indicies of refraction cause a solution to look oily if it is not well mixed
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Bad Primary Standards
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-Na2CO3
-H2SO4
-HCl
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Systematic Errors (Determinate)
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reproducable
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Random Errors (Indeterminate
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Gausian disstribution
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Accuracy
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how close to the correct value
(error)
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Precision
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how consistent you are
(deviation)
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absolute error
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mean -actual value
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Relative Error
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actual error/ actual value
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absolute deviation
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result – mean
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Average Deviation
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(?|x-mean|)/ N
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Rel. Avg. Dev.
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[(?|x-mean|)/ N ] / mean
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Std. Dev.
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v {[?(x – mean)^2] / N-1}
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aA + bB –> cC + dD
Find Keq
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[C]^c x [D]^d / [A]^a x [B]^b
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Combine
H2CO3 –> H+ + HCO3- Keq1
HCO3- –> H+ + CO32- Keq2
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H2CO3–> 2H+ + CO3 2-
Keq = (Keq1)(Keq2)
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Reverse:
H2CO3 –> H+ + HCO3-
Keq1 = 4.45×10^-7
Keq = (Keq1)(Keq2)
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HCO3- + H+ –> H2CO3
Keq= 1/Keq1 = 2.25×10^6
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Order of precipitation
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smaller Ksp precipitates first
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Common Ion Effect
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a salt will be less soluble if one of its constituent ions is already present in the solution
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Acids and Bases
Arrhenius
Bronsted-Lowry
Lews
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H+ and OH-
H+ donar and H+ acceptor
e- acceptor and e- donar
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Strong Acids
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HCl
HNO3
H2SO4
HClO4
HBr
HI
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Weak Acids
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HOAc
Carboxylic Acids
HF
H2S
H3PO4
H2CO3
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Strong Bases
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NaOH
KOH
LiOH
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Weak Bases
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NH3
R-NH2
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Find Kb
NH3 + H2O –> NH4+ + OH-
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Kb = [NH4+]x[OH-] / [NH3]
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Kjeldalhl For N
(volumetric)
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-sample placed in boiling H2SO4–> NH4+ + CO2 + H2O
-add excess base to convert NH4+ –> NH3
-distill the NH3 into a known conc. of HCl (some of the HCl will be neutralized, but not all)
-titrate the excess HCl with NaOH
-the difference in moles correlates to the moles of NH3 consumed
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What is the end point?
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observed in lab –> color change
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What is the equivalence point?
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mol of titrant = mol of anlayte
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ionic strength
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1/2 ?CnZn^2 = µ
C=Concentration
Z=Charge
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Activity of M
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AM = [M]?M
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Debye- Huckle Equation
(for calculating ?)
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log? = (-0.51 x z^2vµ) / (1 + {[?vµ]/305})
? = activity coefficient
z = ion charge
µ = ionic strength in [M]
? = hydrated ionic raiums in ppm
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Thermal Expansion
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(conc1/ dens1) = ( conc2/ dens2)
[M]( 1 ± coeff. of therm. expan)(? temp)=
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Comparing an answer with the accepted answer within a specified confidence limit of a small data set (replication of a measurement with one overall mean and standard deviation)
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Use the Confidence Interval:
µ = [m ± (ts)] / vn
look up t value for whatever degrees of freedom your data has (df = n-1)
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Comparing two different methods to see whether they agree with each other within a specified confidence limit. Measuring a qunatity multiple times with different methods; each data set has its own mean and standard deviation.
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tcalc = |m1-m2| / spooled
calculate this t and compare to a t value from the table
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Comparing whether 2 methods agree with each other when a sample is measured once by one method and then again by another. Then different sample is measured once by method 1 and once by method 2. This is repeated for n different samples
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1.Standard Deviation of the differences:
sd=v( [? (di – d)^2] n-1 )
di=difference between two methods
d= mean of the differnces
2. tcalc=(|d|/sd) v n
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variance
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s^2
(s=std. dev)
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coefficient of variation
(relative standard deviation)
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(s/m) x 100
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Standard Error of the Mean
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s / vn