Chem 327 Exam 1

Front 1

What are the four steps of chemical analysis

Back 1

1. For the question
2. Select procedures
3. Sample Prep
4. analysis

Front 2

What do the following prefixes mean
tera giga mega

Back 2

tera 10^12, giga 10^9, mega 10^6

Front 3

what do the following prefixes mean
kilo hecto deca

Back 3

kilo 10^3 hecto 10 ^2 deca 10^1

Front 4

What do the following prefixes mean
deci centi milli

Back 4

deci 1-^-1 centi 10^-2 milli 10^-3

Front 5

What do the following prefixes mean
micro nano pico femto

Back 5

micro 10^-6, nano 10^-9, pico 10^-12, femto 10^-15

Front 6

what is an angstrom

Back 6

10^-10 meters

Front 7

What is molarity

Back 7

moles substance/ L solution

Front 8

what is formal concentration?

Back 8

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

Front 9

How is % wt. definied

Back 9

mass solute/mass total solution

Front 10

how is % volume defined

Back 10

volume solute/ volume total solution

Front 11

What is molality

Back 11

moles solute/ kg solvent

Front 12

How are ppm and ppb defined

Back 12

1 ppm= 1g substance/ 1X 10^6 gram solution, 1ppb= 1 g substance/ 1X10^9 gram solution

Front 13

What is the dilution equation

Back 13

M1V1=M2V2

Front 14

Why does boyance affect mass measurements?

Back 14

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

Front 15

Define each term in the boyance correction equation
m=m'(1-da/dw)/ (1-da/d)`

Back 15

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

Front 16

When do boyance errors occur during mass measuremetns

Back 16

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.

Front 17

Why does temperature effect volumetric measurments

Back 17

both the liquid being measured and the class expand as the temperature rises. This changes the volume that is acually delivered

Front 18

What is the calibration equation used for volumetric glassweare

Back 18

true volume= mass of water X correction factor (ml/g)

Front 19

How is volumetric glassweare calibrated

Back 19

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.

Front 20

What are the sig fig rules for log. ie. how many digits shoudl be included in log (339)

Back 20

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

Front 21

What are the SF rules for antilogs i.e. antilog (-3.42) or 10^-3.42

Back 21

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

Front 22

define systematic or determinate error

Back 22

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

Front 23

define random error or indeterminate error

Back 23

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

Front 24

define precision

Back 24

a meausre of the reproducibility of your results

Front 25

define accuracy

Back 25

how close a measured value is to a true value

Front 26

define absolute uncertainty

Back 26

expresses the margin of uncertainty associated with a measurement e.g. 50 =/- 0.02 ml

Front 27

define relativie uncertainty and give its equation

Back 27

reltive uncertainty compares the absolute uncertainty with its asociated measurement. The equation is relative uncertainty= absolute uncertainty/ magnitude of measurement

Front 28

Does systematic error effect accuracy or precision

Back 28

Accuracy. The measurements will continue to be precise but they will be centered around the wrong value

Front 29

Does random error effect accuracy or precision

Back 29

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

Front 30

How is uncertaintly propagated when adding or substracting

Back 30

The induvidual ABSOLUTE errors are squared and sumed. The sum of the squares is square rooted. This gives the absolute uncertaintly of the response

Front 31

How is uncertainty propagated when multiplying and dividing

Back 31

calcuate the relative percent errors, square then sum then take the square root. This gives the relative percent uncertainty of the answer

Front 32

How do you convert relative % uncertainty to absolute error

Back 32

divide by 100 to get back to the decimal then multiple by the magnitude of the measurement

Front 33

how is error propagated in mixed operations

Back 33

do addition and subtraction first and calcuate the absolute error. Then calcuate the % relative error and carry out multiplication like normal

Front 34

What is the real rule of significant figures

Back 34

the first uncertain figure of the answer is the last significant figure (the decimal places of the mesaurement and the absolute uncertainty should match)

Front 35

what type of error does statistics deal with

Back 35

random (indeterminate) error only

Front 36

WHat aspects of a gaussian distribution to the mean and standard deviation determine

Back 36

the mean determines the center and the standard deviation determines the width. The larger the standard deviation the more short and wide the curve

Front 37

how do you calculate relative standard deviation

Back 37

standard deviation divided by the average

Front 38

what is variance

Back 38

variance is the square of the standard deviation

Front 39

What percentage of measurements lie within +/- 1 standard deviation from the mean of an ideal gaussian distribution

Back 39

68.3%

Front 40

What percentage of measurements lie within +/- 2 standard deviation from the mean of an ideal gaussian distribution

Back 40

95.5%

Front 41

What percentage of measurements lie within +/- 3 standard deviation from the mean of an ideal gaussian distribution

Back 41

99.7%

Front 42

what is a confidence interval

Back 42

a range of values within which there is a specified probability of finding the true mean

Front 43

How do you determine the degrees of freedom to use for calculating a confidence interval

Back 43

The degrees of freedom is n-1 or number of data points -1

Front 44

How do you find the T value for determining a confidence interval

Back 44

find the degress of freedom an the % confidence desired then use the T table

Front 45

T/F A 90% confidene interval is smaller than a 50% confidence interval

Back 45

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

Front 46

what is the null hypothesis of the student's T test

Back 46

the means are not different

Front 47

how many degrees of freedom are used to find the T value when doing a comparison of means test

Back 47

n1+n2-2

Front 48

What does it mean it Tcalc> T table for a comparision of means test? What if Tcalc<T table

Back 48

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)

Front 49

what is the fancy name for a known sample

Back 49

Standard Refereance Material

Front 50

How would calculate a confidence interval if you knew the population standard deviation

Back 50

You would use the T value for infite degress of freedom

Front 51

what equation would you use to compare your mean to a known value

Back 51

T calc=(u-x) * (√n)/s)

Front 52

How is a Grubbs test for an outlier preformed

Back 52

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

Front 53

What assumptions concerning vertical deviations are employed when using the least squares method for finding a best fit line (2)

Back 53

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

Front 54

describe the "ranges" of a calibration curve

Back 54

1. linear range
2. dynamic range- data no longer shows a linear relationship but it can still be used

Front 55

what is an R squared value

Back 55

R squared describes how well a best fit line fits the data. The value ranges from 0-1 with 1 being a perfect fit

Front 56

what are specifications

Back 56

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)

Front 57

define selectivity

Back 57

being able to distinguish analyte from other species in the sample

Front 58

define sensitivity

Back 58

the capability of responding reliably and measurably to changes in analyte concentration

Front 59

Define each type of blank
method-
reagent-
field-

Back 59

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

Front 60

describe a spike recovery

Back 60

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)

Front 61

How do you calculate spike recovery

Back 61

%recovery= Cspiked-Cunspiked/ Cadded * 100

Front 62

What is a calibration check

Back 62

analyze solutions that contain a known amount of analyte and make sure they match the calibration curve

Front 63

What are preformance test samples

Back 63

blind samples that are used a a quality control method to eliminate bias introduced when an analyst knows then concentration

Front 64

What is the detection limit

Back 64

The smallest quantity of analyte that is "significantly different" from the blank

Front 65

What is the difference between the detection limit and the lower limit of quantitation

Back 65

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

Front 66

What is the reporting limit

Back 66

the concentration below which regulations dictate that a given analyte is reported as "not detected" Usually 5 to 10 times above the detection limit

Front 67

What is the difference between signal detection limit and detection limit

Back 67

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

Front 68

what does the "s" stand for in the equations ydl=yblank + 3s, MDC= 3s/m, LOQ= 10s/m? What does the m stand for?

Back 68

the S standands for the standard deviation of the y values (the measurements) the m is the slope of the calibration line

Front 69

describe light waves

Back 69

perpendicular oscillating electric and magnetic fields

Front 70

what is wave number

Back 70

the inverse of wavelength, usually expressed as cm-1
don't forget to inverse first before doing any conversions

Front 71

what is the range of wavelengths and frequencies for x rays and what do they do to molecules

Back 71

Frequency= 10^18
wavelength = 10^-11-10^-8
they cause bond breaking and ionization

Front 72

what is the range of wavelengths and frequencies for UV rays and what do they do to molecules

Back 72

Frequency =10^16
wavelenght 10^-8-10^-6
they cause electronic excitation

Front 73

what is the range of wavelengths and frequencies for visable light and what do they do to molecules

Back 73

Frequency 10^15
wavelength 400 (violet)- 700 (red) nm (10^-7)
many cause electronic exictiation but only near the violet end

Front 74

what is the range of wavelengths and frequencies for infrared rays and what do they do to molecules

Back 74

Frequency= 10^14-10^12
wavelength= 10^-6-10^-3
causes bond vibration and streching

Front 75

what is the range of wavelengths and frequencies for microwaves and what do they do to molecules

Back 75

Frequency= 10^9-10^8
wavelength= 10^-3 to 10^-1
causes bond rotation

Front 76

Which end of the visible spectrum is most energetic

Back 76

the violet end, 400nm (shorter wavelength, larger frequency, larger energy)

Front 77

what is the equation for transmitance

Back 77

T=P/Po

Front 78

What are the components of a single beam spectrophotometer

Back 78

1. light source
2. monochrometer
3. sample
4. light dectector
5. computer/ meter/ display

Front 79

How do you convert from transmitance to absorbance

Back 79

A=-logT (T is expressed as a decimal, not a percent)

Front 80

What are the units of molar absorbtivity

Back 80

M-1cm-1

Front 81

What are the assumptions of beer's law

Back 81

1. the light is monochromatic
2. the sample is dilute

Front 82

what is the probabilty of a false positive using a +3s detection limit on a gaussian curve?
T distribution

Back 82

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%.

Front 83

What is the probability of detecting a false negative using a +3s dection limit on a guassian curve

Back 83

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

Front 84

Complement colors
red
orange
yellow

Back 84

red & green
orange & blue
yellow & violet

Front 85

Why is it necessary to use a flat peak portion of the absorbance spectrum when applying beer's law

Back 85

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

Front 86

Why is it necessary to use dilute samples when applying beer's law

Back 86

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)

Front 87

Why is it best to use a spectroeter at intermediate levels of absorbance (0.3 to 2)

Back 87

too much light gets through- hard to distinguish from the blank
too little light- hard to measure intensity

Front 88

What is the main benefit of a double beam spectrometer

Back 88

it reduces the error assocaited with decetor or response drift that can occur between the reference and analyte measurements

Front 89

Describe a double beam spectrometer

Back 89

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

Front 90

What types of light are usually used in spectroscopy and what sources are used to produce them
when do we swtch

Back 90

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

Front 91

What is a monochrometer and how does it work

Back 91

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

Front 92

What balance must be achieved with exit slit width

Back 92

A narrow slit decreases the selected bandwidth which increases the resolution but decreases the energy reaching the detector which results in increased noise

Front 93

describe a photomultipler tube spectrometer detector

Back 93

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

Front 94

What is the disadvantage to the photomultipler tube dectetion method

Back 94

only one wavelength can be measured at a time

Front 95

Describe a photodiode array

Back 95

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.

Front 96

What is the advantage to a photodiode array? Disadvantage?

Back 96

advantage- detects entire sprectrum at once
disadvantage-about an order of magnitude lower resolution than a dispersive spec.

Front 97

T/F the absorbance of a mixture is equal to the sum of the absorbances from all the species at that wavelenth

Back 97

True

Front 98

How can accuracy be improved when analysing the absorbance of a mixture

Back 98

Pick wavelengths where one compound absorbs strongly and one asbors weakly,

Front 99

what is an isobestic point

Back 99

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

Front 100

what is the equation for corrected absorbance ina spectrophotometric titration

Back 100

Abs cor= (total voume/ initial volume) (observed abs)

Front 101

how is the end point detected in a spectrophotometric titration

Back 101

we look for the point where the calibration line on the abs vs. volume added plot flatens

Front 102

At the most basic level, what happens to a molecule that absorbs a photon? Emits a photon?

Back 102

The molecule is promoted to a more energetic state

Front 103

define singlet state

Back 103

the electron spins are opposed (paired)

Front 104

define triplet state

Back 104

the electron spins are parallel (the same)

Front 105

Which is lower energy S1 or T1

Back 105

T1 has lower energy than S1

Front 106

Draw the ground state

Back 106

↑↓
----

Front 107

Draw the S1 state

Back 107

↑
--
↓
--

Front 108

draw the T1 state

Back 108

↑
---
↑
---

Front 109

Assume a molecule absorbs a photon of sufficient energy to promote it from ground state So to S1. What is the usual next event

Back 109

The molecule vibrationally relaxes to a lower level of S1, energy is lost to other molecule via collisions

Front 110

describe an internal conversion

Back 110

a molecule in S1 enters a highly excited vibrational level of So

Front 111

describe an intersystem crossing

Back 111

A molecule in S1 relaxes and then moves to an excited vibrational level of T1

Front 112

How might a molecule relax from S1 back to ground state via emission of heat through collisions (2 ways)

Back 112

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

Front 113

What transition results in phosphorescence?
Flourescence?

Back 113

Phosphorescence is T1 to So
Fluorsecence is S1 to So

Front 114

What transition results in phosphorescence

Back 114

T1 to So

Front 115

T/F Phosphorescence and flurescenec can terminate in any vibrational level of So so long as it is not the ground state

Back 115

True

Front 116

Which occurs at lower energy Phosphorescence or fluroescence

Back 116

Phosphorescence because it invovles a transition from T1 to So which is lower energy than S1 to So

Front 117

Even though Phosphorescene occurs at lower energy than fluorescence it is rarer. Explain why

Back 117

Phosphorescence requires a transition from T1 to So. Molecules in the T1 state are likely to undergo collisional deactivation before phosphorescence can occur

Front 118

Describe the relationship between fluorescence and absorbance spectra

Back 118

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

Front 119

Besides electronic transitions what is another consquence of absorption of light

Back 119

The breaking of chemical bonds (photochemistry), Also, some chemical reactions can release energy as light (chemoluminescence)

Front 120

define luminescence

Back 120

any emission of electromagnetic radiation. Includes fluorescence, phosphorescence, and other processes

Front 121

How is luminescence measured

Back 121

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.

Front 122

Why is luminescence more sensitive than absorption

Back 122

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)

Front 123

Describe a luminescence detector

Back 123

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

Front 124

What is the luminescence equation

Back 124

I=kPoC
k is a constant
Po is the incident wavelenth
C is the concentration
and I is the intensity of luminescence

Front 125

describe self absorption and how it effects the spectra

Back 125

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

Front 126

What to things must you do to a balance before you weight (besides making sure its clean and level)

Back 126

calibrate and tare

Front 127

how should a hygroscopic material be weight

Back 127

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

Front 128

What are some sources of determinate error when weight

Back 128

evaporation of a liquid, fingerprints, weighing hot objects

Front 129

What is the chemical name for THAM

Back 129

tris-(hydroxylmethyl)aminomethane

Front 130

What is THAM?

Back 130

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

Front 131

Why is THAM a good primary standard base (6 reasons)

Back 131

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

Front 132

What is the balanced chemical reaction for the THAM titration

Back 132

THAM + HCL => (HOCH2)3CNH3+ + Cl-

Front 133

why is it necessary to standardize an aproximate solution of NaOH

Back 133

Analytical quality sodium hydroxie contains small amounts of impurites including water and carbonate.

Front 134

What does KHP stand for

Back 134

Potassium hydrogen phthalate

Front 135

Why is KHP used for standardizing bases (4)

Back 135

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

Front 136

What is the balance reaction for the KHP titration

Back 136

KHP +NaOH => KHC8H4O4 + H2O + Na+ (the Na plucks the acidic hydrogen from KHP giving water and the KHP anion

Front 137

What is the acid base indicator used in the THAM + HCl titration and what is its color change? At what pH does this occur

Back 137

bromocresol green
it is yellow as an acid and blue as a base it changes color a pH of 4.7 (intermediate green color)

Front 138

What is the pH indicator used in the KHP + NaOH titration? What is it's color change and at what pH does this occur?

Back 138

The indicator is phenophthalein. It is colorles when acidic and bright fusha when basic. The pH changes at about 9.2

Front 139

How do you determine weight percent

Back 139

mass of analyte/mass sample

Front 140

what is the purpose of a positive control

Back 140

-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

Front 141

In what order were the reagents added to the iron reaction

Back 141

1. HCL
2. NH2OH
3. NaOAc
4.Bipryidyl

Front 142

what was the purpose of adding HCL to the iron mixture

Back 142

it kept the pH low so that the iron complex would be stable

Front 143

What was the purpose of adding NH2OH to the iron mixture

Back 143

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

Front 144

What was the purpose of adding NaOAc to the iron mixture

Back 144

it is a buffer

Front 145

What was the purpose of adding bipyridyl to the iron mixture

Back 145

it is the reagent that forms the red complex with Fe2+

Front 146

What is the advantage to using the precipitation from homogenous solution method for analysing Ca content

Back 146

The precipitate forms slowly which gives larger crystals that are easier to handle. There are no zones of contact between relativley concentrated solutions

Front 147

What is the purpose of the urea (NH2)2CO in the calcium oxalate precipitation

Back 147

When urea is heated it begins a chain reaction of equations that evenually generate the oxalate ion needed to precipitate the Ca ions

Front 148

Write the reactions that generate the calcium oxalate from urea + water + heat

Back 148

(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)

Front 149

How would you calculate % Ca of a sample from the final mass of calcium oxalate

Back 149

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)

Front 150

What is the pupose of each of the following reactants in the calcium oxalate precipitation
urea
ammonium oxalate

Back 150

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.