Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
150 Cards in this Set
- Front
- Back
What are the four steps of chemical analysis
|
1. For the question
2. Select procedures 3. Sample Prep 4. analysis |
|
What do the following prefixes mean
tera giga mega |
tera 10^12, giga 10^9, mega 10^6
|
|
what do the following prefixes mean
kilo hecto deca |
kilo 10^3 hecto 10 ^2 deca 10^1
|
|
What do the following prefixes mean
deci centi milli |
deci 1-^-1 centi 10^-2 milli 10^-3
|
|
What do the following prefixes mean
micro nano pico femto |
micro 10^-6, nano 10^-9, pico 10^-12, femto 10^-15
|
|
what is an angstrom
|
10^-10 meters
|
|
What is molarity
|
moles substance/ L solution
|
|
what is formal concentration?
|
The concentration of a substance if it were not to dissociate. i.e. 1M Acetic acid isn't really 1 molar because its a weak acid and we get some H+ some OAc - and some HOAc. Formal concentration ignores this fact and defines the concentration of this solution as simply 1M
|
|
How is % wt. definied
|
mass solute/mass total solution
|
|
how is % volume defined
|
volume solute/ volume total solution
|
|
What is molality
|
moles solute/ kg solvent
|
|
How are ppm and ppb defined
|
1 ppm= 1g substance/ 1X 10^6 gram solution, 1ppb= 1 g substance/ 1X10^9 gram solution
|
|
What is the dilution equation
|
M1V1=M2V2
|
|
Why does boyance affect mass measurements?
|
The apparent weight of the objects is less than the true weight by an amount equal to the weight of the air displaced by the object
|
|
Define each term in the boyance correction equation
m=m'(1-da/dw)/ (1-da/d)` |
m is the true weight
m' is the weight read from the balance da is the density of air dw is the density of the balance weight d is the density of the object |
|
When do boyance errors occur during mass measuremetns
|
A boyancy error will occur when the density of the object is not equal to the density of the calibration weights (if this is the case, the correction factor reduces to 1 and m=m')
If the object is more dense than the calibraiton weights, it will appear to weigh less than its true weight. If the object is less dense than the calibration weight, it will appear to weight more. |
|
Why does temperature effect volumetric measurments
|
both the liquid being measured and the class expand as the temperature rises. This changes the volume that is acually delivered
|
|
What is the calibration equation used for volumetric glassweare
|
true volume= mass of water X correction factor (ml/g)
|
|
How is volumetric glassweare calibrated
|
A known volume is dispensed and weighed. This mass is multiplied by a correction factor which is simply the density of water at the paticular temperature. This correction gives the volume dispensed.
|
|
What are the sig fig rules for log. ie. how many digits shoudl be included in log (339)
|
The number of digits in the mantissa (the decimal portion of the log) should equal the number of signifiant figures in the original number. So, log 339 would be 2.530 with 3 SFs in the decimal portion
|
|
What are the SF rules for antilogs i.e. antilog (-3.42) or 10^-3.42
|
The number of digits in the decimal portion of the antilog should equal the number of digits in the decimal place of the original number. So, 10^ -3.42 should be written as 3.8 x 10^-4 because there are two digits in the decimal of 3.42
|
|
define systematic or determinate error
|
an error that is repeatable if the measurement is made the same way over again. It should be correctable. Examples include an imporperly calibrated pH meter or a faulty buret
|
|
define random error or indeterminate error
|
arises from limitations in ability to make precise measurements and random fluctuations. It cannot be corrected Examples include reading scales and electrical nose in an insturment
|
|
define precision
|
a meausre of the reproducibility of your results
|
|
define accuracy
|
how close a measured value is to a true value
|
|
define absolute uncertainty
|
expresses the margin of uncertainty associated with a measurement e.g. 50 =/- 0.02 ml
|
|
define relativie uncertainty and give its equation
|
reltive uncertainty compares the absolute uncertainty with its asociated measurement. The equation is relative uncertainty= absolute uncertainty/ magnitude of measurement
|
|
Does systematic error effect accuracy or precision
|
Accuracy. The measurements will continue to be precise but they will be centered around the wrong value
|
|
Does random error effect accuracy or precision
|
precision. Random error is equaly likely to be positive or negative. It will cause your measurements to fall within a range of your true value
|
|
How is uncertaintly propagated when adding or substracting
|
The induvidual ABSOLUTE errors are squared and sumed. The sum of the squares is square rooted. This gives the absolute uncertaintly of the response
|
|
How is uncertainty propagated when multiplying and dividing
|
calcuate the relative percent errors, square then sum then take the square root. This gives the relative percent uncertainty of the answer
|
|
How do you convert relative % uncertainty to absolute error
|
divide by 100 to get back to the decimal then multiple by the magnitude of the measurement
|
|
how is error propagated in mixed operations
|
do addition and subtraction first and calcuate the absolute error. Then calcuate the % relative error and carry out multiplication like normal
|
|
What is the real rule of significant figures
|
the first uncertain figure of the answer is the last significant figure (the decimal places of the mesaurement and the absolute uncertainty should match)
|
|
what type of error does statistics deal with
|
random (indeterminate) error only
|
|
WHat aspects of a gaussian distribution to the mean and standard deviation determine
|
the mean determines the center and the standard deviation determines the width. The larger the standard deviation the more short and wide the curve
|
|
how do you calculate relative standard deviation
|
standard deviation divided by the average
|
|
what is variance
|
variance is the square of the standard deviation
|
|
What percentage of measurements lie within +/- 1 standard deviation from the mean of an ideal gaussian distribution
|
68.3%
|
|
What percentage of measurements lie within +/- 2 standard deviation from the mean of an ideal gaussian distribution
|
95.5%
|
|
What percentage of measurements lie within +/- 3 standard deviation from the mean of an ideal gaussian distribution
|
99.7%
|
|
what is a confidence interval
|
a range of values within which there is a specified probability of finding the true mean
|
|
How do you determine the degrees of freedom to use for calculating a confidence interval
|
The degrees of freedom is n-1 or number of data points -1
|
|
How do you find the T value for determining a confidence interval
|
find the degress of freedom an the % confidence desired then use the T table
|
|
T/F A 90% confidene interval is smaller than a 50% confidence interval
|
False, a 50% interval is smaller. To be 90% sure that we'll find the true mean, we have to have a large interval, if we are only 50% sure, we'll have a smaller value. Numerically, the t value for a 90% interval is larger than that for a 50% interval with the same DOF
|
|
what is the null hypothesis of the student's T test
|
the means are not different
|
|
how many degrees of freedom are used to find the T value when doing a comparison of means test
|
n1+n2-2
|
|
What does it mean it Tcalc> T table for a comparision of means test? What if Tcalc<T table
|
if Tcalc> T table, the two means are significantly different
If Tcalc<T table, the means are not different (note that we cannot say that the means are the same) |
|
what is the fancy name for a known sample
|
Standard Refereance Material
|
|
How would calculate a confidence interval if you knew the population standard deviation
|
You would use the T value for infite degress of freedom
|
|
what equation would you use to compare your mean to a known value
|
T calc=(u-x) * (√n)/s)
|
|
How is a Grubbs test for an outlier preformed
|
Calculate the mean and standard deviation. Line the data up in order and look for a questionable values. Find G calc (questionable -average/ s) and compare to the table. If Gcalc> Gtable the questionable point should be discarded. Recalculate the new mean and standard deviation
|
|
What assumptions concerning vertical deviations are employed when using the least squares method for finding a best fit line (2)
|
1. The experimental uncertainties in the y values are greater than the uncertainties in the x values
2. The uncertainties for all of the y values are the same |
|
describe the "ranges" of a calibration curve
|
1. linear range
2. dynamic range- data no longer shows a linear relationship but it can still be used |
|
what is an R squared value
|
R squared describes how well a best fit line fits the data. The value ranges from 0-1 with 1 being a perfect fit
|
|
what are specifications
|
state how good measurements need to be and what procedural precautions will be used (sampling requirements, accuracy and precision, rates of false +/-, selectivity, sensitivity, accetable blank values, recovery of fortification, calibration checks, quality control)
|
|
define selectivity
|
being able to distinguish analyte from other species in the sample
|
|
define sensitivity
|
the capability of responding reliably and measurably to changes in analyte concentration
|
|
Define each type of blank
method- reagent- field- |
method blank-sample containing all components except analyte
reagent blank-similar to a method blank but has not been subjected to all sample preparation procedures field- similar to method blank but it has been exposed to the site of sampling |
|
describe a spike recovery
|
a known quantity of analyte is added to a sample to test whether the response to a sample is the same as that expected from a calibration curve (example if a sample contains 10g and we add 5 g, we should expect to detect 15g)
|
|
How do you calculate spike recovery
|
%recovery= Cspiked-Cunspiked/ Cadded * 100
|
|
What is a calibration check
|
analyze solutions that contain a known amount of analyte and make sure they match the calibration curve
|
|
What are preformance test samples
|
blind samples that are used a a quality control method to eliminate bias introduced when an analyst knows then concentration
|
|
What is the detection limit
|
The smallest quantity of analyte that is "significantly different" from the blank
|
|
What is the difference between the detection limit and the lower limit of quantitation
|
the detection limit describes a point that is distinguishible from the blank but too small for accurate measurement. The lower limit of quantiation (10s/m)is the smallest amound that can be measured with resonable accuracy
|
|
What is the reporting limit
|
the concentration below which regulations dictate that a given analyte is reported as "not detected" Usually 5 to 10 times above the detection limit
|
|
What is the difference between signal detection limit and detection limit
|
signal detection limit is the limit of what is being analyzed e.g. absorbance. Dectection limit is the analyte that produced that signal e.g. concentration
|
|
what does the "s" stand for in the equations ydl=yblank + 3s, MDC= 3s/m, LOQ= 10s/m? What does the m stand for?
|
the S standands for the standard deviation of the y values (the measurements) the m is the slope of the calibration line
|
|
describe light waves
|
perpendicular oscillating electric and magnetic fields
|
|
what is wave number
|
the inverse of wavelength, usually expressed as cm-1
don't forget to inverse first before doing any conversions |
|
what is the range of wavelengths and frequencies for x rays and what do they do to molecules
|
Frequency= 10^18
wavelength = 10^-11-10^-8 they cause bond breaking and ionization |
|
what is the range of wavelengths and frequencies for UV rays and what do they do to molecules
|
Frequency =10^16
wavelenght 10^-8-10^-6 they cause electronic excitation |
|
what is the range of wavelengths and frequencies for visable light and what do they do to molecules
|
Frequency 10^15
wavelength 400 (violet)- 700 (red) nm (10^-7) many cause electronic exictiation but only near the violet end |
|
what is the range of wavelengths and frequencies for infrared rays and what do they do to molecules
|
Frequency= 10^14-10^12
wavelength= 10^-6-10^-3 causes bond vibration and streching |
|
what is the range of wavelengths and frequencies for microwaves and what do they do to molecules
|
Frequency= 10^9-10^8
wavelength= 10^-3 to 10^-1 causes bond rotation |
|
Which end of the visible spectrum is most energetic
|
the violet end, 400nm (shorter wavelength, larger frequency, larger energy)
|
|
what is the equation for transmitance
|
T=P/Po
|
|
What are the components of a single beam spectrophotometer
|
1. light source
2. monochrometer 3. sample 4. light dectector 5. computer/ meter/ display |
|
How do you convert from transmitance to absorbance
|
A=-logT (T is expressed as a decimal, not a percent)
|
|
What are the units of molar absorbtivity
|
M-1cm-1
|
|
What are the assumptions of beer's law
|
1. the light is monochromatic
2. the sample is dilute |
|
what is the probabilty of a false positive using a +3s detection limit on a gaussian curve?
T distribution |
0.15 % A false positive occcurs when a measurement that should fall within the blank distribution is mistaken for being within a measurement distribution. A 3s dection limit means that 99.7% of the measurements about the blank fall within the range of the blank. Half of the remaining measurements (0.3/2) = 0.15% are above this limit so they can be detected as positive when they are really not. The probablity of a false positive on a T distribution is about 1%.
|
|
What is the probability of detecting a false negative using a +3s dection limit on a guassian curve
|
There is a 50% probability of having a false negative. A false negative occurs when a measurement that should be within the sample distribution falls within the blank distrubution instead
|
|
Complement colors
red orange yellow |
red & green
orange & blue yellow & violet |
|
Why is it necessary to use a flat peak portion of the absorbance spectrum when applying beer's law
|
If a flat region is chosen, small variations in wavelenth do not lead to signifiant changes in absorbance. If a steep region is chosen, small variations lead to large changes in absorbance (see graph)
the peak is used because it gives the greatest sensitivity |
|
Why is it necessary to use dilute samples when applying beer's law
|
high concentrations decrese hte distance between particles leading to more interferace. They also decrease the light reaching the detector making the measurements less sensitive (if too little light gets through, intensity is hard to measure)
|
|
Why is it best to use a spectroeter at intermediate levels of absorbance (0.3 to 2)
|
too much light gets through- hard to distinguish from the blank
too little light- hard to measure intensity |
|
What is the main benefit of a double beam spectrometer
|
it reduces the error assocaited with decetor or response drift that can occur between the reference and analyte measurements
|
|
Describe a double beam spectrometer
|
A light source is passed through a scanning monochrometer to select a narrow bandwidth. The light beam is then passed through a chopper which alternates the beam several times per second between the reference and sample cuvet. The beams are then send through a detector and the results are displayed
|
|
What types of light are usually used in spectroscopy and what sources are used to produce them
when do we swtch |
1. visible light and infrared by tungesten filament (320-2500nm)
2. UV light with deuterium lamp (200 to 400) switch is made at 360 nm from deuterium to tungsten |
|
What is a monochrometer and how does it work
|
it breaks light into its component wavelenghts and selects the desired one
1. Radiation from the light source is made into parallel beams by a collimanating mirror 2.The parallel ways hit the grating and the different wavelenths are diffracted at different angles 3. The diffracted ligth hits a second mirror which focuses each wavelenth at a different point 4.A narrow band of wavelengths is detected towards the exit slit and allowed to pass through the sample Rotation of the grating allows different wavelengths to pass throug the exit slit |
|
What balance must be achieved with exit slit width
|
A narrow slit decreases the selected bandwidth which increases the resolution but decreases the energy reaching the detector which results in increased noise
|
|
describe a photomultipler tube spectrometer detector
|
light strikes a photosensitive cathode are electrons are emited these strike a seond surface called a dynode and more electrons are released. This process continues until about 10^6 electrons are released and collected for each photon striking the cathode. This translates very low light intesities into measurable electric signals
|
|
What is the disadvantage to the photomultipler tube dectetion method
|
only one wavelength can be measured at a time
|
|
Describe a photodiode array
|
White light passes through a sample. The beam then enters a polychromator which disperses the light into its wavelengths and directs it to the diode array.
|
|
What is the advantage to a photodiode array? Disadvantage?
|
advantage- detects entire sprectrum at once
disadvantage-about an order of magnitude lower resolution than a dispersive spec. |
|
T/F the absorbance of a mixture is equal to the sum of the absorbances from all the species at that wavelenth
|
True
|
|
How can accuracy be improved when analysing the absorbance of a mixture
|
Pick wavelengths where one compound absorbs strongly and one asbors weakly,
|
|
what is an isobestic point
|
it is the point where two spectra of items in a mixture cross. For any mixture measure at the same wavelength with the same total cocentration, the IB point will be the same. It occurs when Ex=Ey (at the particular wavenlength) and [x] + [y] is constant
A=Esameb([x]+[y]) it is good evidence that only two principle species are present |
|
what is the equation for corrected absorbance ina spectrophotometric titration
|
Abs cor= (total voume/ initial volume) (observed abs)
|
|
how is the end point detected in a spectrophotometric titration
|
we look for the point where the calibration line on the abs vs. volume added plot flatens
|
|
At the most basic level, what happens to a molecule that absorbs a photon? Emits a photon?
|
The molecule is promoted to a more energetic state
|
|
define singlet state
|
the electron spins are opposed (paired)
|
|
define triplet state
|
the electron spins are parallel (the same)
|
|
Which is lower energy S1 or T1
|
T1 has lower energy than S1
|
|
Draw the ground state
|
↑↓
---- |
|
Draw the S1 state
|
↑
-- ↓ -- |
|
draw the T1 state
|
↑
--- ↑ --- |
|
Assume a molecule absorbs a photon of sufficient energy to promote it from ground state So to S1. What is the usual next event
|
The molecule vibrationally relaxes to a lower level of S1, energy is lost to other molecule via collisions
|
|
describe an internal conversion
|
a molecule in S1 enters a highly excited vibrational level of So
|
|
describe an intersystem crossing
|
A molecule in S1 relaxes and then moves to an excited vibrational level of T1
|
|
How might a molecule relax from S1 back to ground state via emission of heat through collisions (2 ways)
|
1. S1 to R1 internal conversion to So R2 to ground state
2. S1 to R1 intersystem crossing to T1, R3, intersystem crossing to So, R4 to ground state So |
|
What transition results in phosphorescence?
Flourescence? |
Phosphorescence is T1 to So
Fluorsecence is S1 to So |
|
What transition results in phosphorescence
|
T1 to So
|
|
T/F Phosphorescence and flurescenec can terminate in any vibrational level of So so long as it is not the ground state
|
True
|
|
Which occurs at lower energy Phosphorescence or fluroescence
|
Phosphorescence because it invovles a transition from T1 to So which is lower energy than S1 to So
|
|
Even though Phosphorescene occurs at lower energy than fluorescence it is rarer. Explain why
|
Phosphorescence requires a transition from T1 to So. Molecules in the T1 state are likely to undergo collisional deactivation before phosphorescence can occur
|
|
Describe the relationship between fluorescence and absorbance spectra
|
Fluorescence occurs at a lower energy than absorbance. It is roughly the mirror image of absorbance because the vibrational levels are roughly equal and the transition probabilites are similar
|
|
Besides electronic transitions what is another consquence of absorption of light
|
The breaking of chemical bonds (photochemistry), Also, some chemical reactions can release energy as light (chemoluminescence)
|
|
define luminescence
|
any emission of electromagnetic radiation. Includes fluorescence, phosphorescence, and other processes
|
|
How is luminescence measured
|
A sample is excited at a wavelength it absorbs and the wavelength of maximum emission is observed . The observation is made perpendicular to the incident direction to minimize the detection of scattered radiation.
|
|
Why is luminescence more sensitive than absorption
|
It is much easier to detect a light sample against a dark background than detecting a dark sample against a light backgroud (stadium candles example)
|
|
Describe a luminescence detector
|
A light source sends light to an excitation monochromater where one wavelength is selected. the light is sent through a sample cell where luminescence occurs at many wavelengths, These resultant wavelengths pass through another monochromater which selects for a dection wavelength. this wavelength is sent to the detector
|
|
What is the luminescence equation
|
I=kPoC
k is a constant Po is the incident wavelenth C is the concentration and I is the intensity of luminescence |
|
describe self absorption and how it effects the spectra
|
if the concentration of the analyte bceomes too great neighboring unexcited molecules absorb light from the excited molecule before the light can escape from the cuvet, this leads to an apparent decrease in fluorescence intensity at hight concentrations, the molecule quencehs its own emission
|
|
What to things must you do to a balance before you weight (besides making sure its clean and level)
|
calibrate and tare
|
|
how should a hygroscopic material be weight
|
You should weight by difference. Weigh a weight bottle, stoper and the material. Place it on the balance and tare. Remove some material from the bottle and place in into the reaction vessel. Note the difference as a negative value
|
|
What are some sources of determinate error when weight
|
evaporation of a liquid, fingerprints, weighing hot objects
|
|
What is the chemical name for THAM
|
tris-(hydroxylmethyl)aminomethane
|
|
What is THAM?
|
THAM is a primary standard weak base. It's structure consists of three HOCH2 groups connected to a central carbon which also has and NH2 group
|
|
Why is THAM a good primary standard base (6 reasons)
|
1. It is non-hygroscopic
2. it does not absorb carbon dioxide from the air 3. it is stable both as the solid and in aqueous solution 4. It can be prepared in very pure form 5. It can be dried without decomposition 6. It reacts quickly and stoichiometrically with the hydronium ion |
|
What is the balanced chemical reaction for the THAM titration
|
THAM + HCL => (HOCH2)3CNH3+ + Cl-
|
|
why is it necessary to standardize an aproximate solution of NaOH
|
Analytical quality sodium hydroxie contains small amounts of impurites including water and carbonate.
|
|
What does KHP stand for
|
Potassium hydrogen phthalate
|
|
Why is KHP used for standardizing bases (4)
|
1. It is easily obtained in pure form
2. It has a high molecular weight 3. it is non hygroscopic 4. it is stable on drying |
|
What is the balance reaction for the KHP titration
|
KHP +NaOH => KHC8H4O4 + H2O + Na+ (the Na plucks the acidic hydrogen from KHP giving water and the KHP anion
|
|
What is the acid base indicator used in the THAM + HCl titration and what is its color change? At what pH does this occur
|
bromocresol green
it is yellow as an acid and blue as a base it changes color a pH of 4.7 (intermediate green color) |
|
What is the pH indicator used in the KHP + NaOH titration? What is it's color change and at what pH does this occur?
|
The indicator is phenophthalein. It is colorles when acidic and bright fusha when basic. The pH changes at about 9.2
|
|
How do you determine weight percent
|
mass of analyte/mass sample
|
|
what is the purpose of a positive control
|
-a calibration check used to check technique
-the answer is known in advance -the goal is to prove that the data generated will be reliable |
|
In what order were the reagents added to the iron reaction
|
1. HCL
2. NH2OH 3. NaOAc 4.Bipryidyl |
|
what was the purpose of adding HCL to the iron mixture
|
it kept the pH low so that the iron complex would be stable
|
|
What was the purpose of adding NH2OH to the iron mixture
|
It is a reducing agent used to make sure all the iron is as Fe2+ (not Fe3+) which is the form that makes the complex
|
|
What was the purpose of adding NaOAc to the iron mixture
|
it is a buffer
|
|
What was the purpose of adding bipyridyl to the iron mixture
|
it is the reagent that forms the red complex with Fe2+
|
|
What is the advantage to using the precipitation from homogenous solution method for analysing Ca content
|
The precipitate forms slowly which gives larger crystals that are easier to handle. There are no zones of contact between relativley concentrated solutions
|
|
What is the purpose of the urea (NH2)2CO in the calcium oxalate precipitation
|
When urea is heated it begins a chain reaction of equations that evenually generate the oxalate ion needed to precipitate the Ca ions
|
|
Write the reactions that generate the calcium oxalate from urea + water + heat
|
(NH2)2CO + H20=> 2NH3 + CO2
2NH3 + H2C2O4=> 2NH4+ +C2O4 2- Ca 2+ + C2O4 2- + H2O => CaC2O4. H2O (make sure to include the water in the molar mass) |
|
How would you calculate % Ca of a sample from the final mass of calcium oxalate
|
Use the final mass of calcium oxalate and divide by the mass of the original sample. This gives a percent of CaCO4. Now change this percent into a decimal and multiply by the % Ca in CaCO4 (27.4296 g Ca/100 calcium oxalate)
|
|
What is the pupose of each of the following reactants in the calcium oxalate precipitation
urea ammonium oxalate |
urea + water and heat gives NH3, a weak base. THe NH3 reacts with the oxalic acid to release the oxalate anion. The Amonium oxalate supplies the oxalate anion and the HCl turns the oxalate anion into oxalic acid. This reactions allows for the slow generation of oxalate ions and controlled precipitation.
|