Final Exam

bulk sample

(also called a gross sample) is taken from the lot for analysis or for archiving (storing for future reference). must be representative of the lot.

flame ionization detector

(eluate is burned in a mixture of H2 and the air) a destructive mass-sensitive detector whose response is proportional to mass of carbon entering per unit time. 100-fold lower detection limit than thermal conductivity, 10^7 linear response range

safety data sheets

-are provided with each chemical sold in the united states -list hazards and precautions for the chemical -provide first aid procedures and instructions for handling spills

standard uncertainty for x decreases with:

-smaller standard deviation in measurements - greater slope of calibration - more replicate measurements of unknown - more calibration points -sample data range closer to center -wide calibration range

critical functions of the lab notebook

-state what you did -state what you observed to be understandable to a stranger

3 types of experimental error

-systematic -random -gross (blunders)

sample preparation

.transforming a sample into a state that is suitable for analysis by dissolving the sample, removing or masking species that interfere with the analysis.

steps in a chemical analysis

1. formulate the question. 2. form analytical procedure. 3. Sampling 4. Sample preparation 5. Analyze 6. Report and interpret 7. Draw conclusions

solutes are ____ and ____ in programmed temperatures

1. strongly retained (trapped) at the column head for most of the time on the column 2. weakly retained when eluted due to higher temperatures and thus appear as sharper peaks

thermal conductivity detector

10^5 linear response range. H2 and He give lowest detection limit. sensitivity increases with increasing filament current decreasing flow rate, lower detector block temperature. nondestructive

molarity

A common measure of solute concentration, referring to the number of moles of solute per liter of solution.

concentration

A measurement of how much (mol) solute exists within a certain volume (L) of solvent

surfactant

A molecule with a hydrophilic end and a hydrophobic end that accumulates a the interface between 2 phases

common ion effect

A salt is less soluble if one of its ions is already present in the solution

What is a segregated heterogeneous material?

A segregated heterogeneous material contains large regions of obviously different compositions.

Grubbs test

A statistical test in which one only point of data may be discarded because it is far away from other other points.

Microwave digestion

A teflon lined bomb is heated in a microwave oven is a convenient means of dissolving difficult samples. metal would absorb microwaves. bomb should be cooled prior to opening to prevent loss of volatile products

Beer Lambert Law

Absorbance increases as concentration increases. The molar absorptivity value is chromophore and wavelength specific. The absorption spectrum is a graph showing how absorbance changes with wavelength.

The chemist has identified some analytical procedures to test for cadmium and mercury in soil samples. What is the next step? Please choose the correct answer from the following choices, and then select the submit answer button. Answer choices

After identifying an appropriate analytical procedure, the next step in a chemical analysis is sampling. Having a representative sample is important to obtain meaningful data.

How are the chromatographic methods divided?

By there mechanism of interaction of solute with the stationary phase

what is the most common supercritical fluid solvent?

Carbon dioxide because it is inexpensive, and eliminates the need for costly disposal.

What are the most accurate grade of burets

Class A burets

T-test

Compares mean values of a continuous variable between 2 categories/groups.

capillary electrophoresis

DNA fragments can be separated and identified by (gas chromatography, capillary electrophoresis).

wet ashing

Destruction of organic matter in a sample by a liquid reagent prior to analysis of an inorganic component.

normal error curve

Gaussian curve with unit area

selected ion monitoring

Graph of detector response versus time when a mass spectrometer monitors just a few selected

van Deemter equation:

H = A + B/u + Cu

retention gap

In gas chromatography, a 3- to 10-m length of empty, silanized capillary ahead of the chromatography column. The retention gap improves the peak shape of solutes that elute close to solvent when large volumes of solvent are injected or when the solvent has polarity from that of the stationary phase.

What is the advantage of using solid-phase extraction for sample preparation in the analysis of caffeine in chocolate over the traditional method?

In the traditional sample preparation process, fat and other nonpolar substances were extracted from the chocolate using an organic solvent. The caffeine was then extracted from the sample using hot water. Finally, fine particles that could ruin the expensive chromatography column were removed with repeated centrifugation and filtration. Solid-phase extraction is able to replace these steps, reducing the sample preparation time. In solid-phase extraction, caffeine and other nonpolar substances are retained on the silica column. Polar, water-soluble substances are washed from the column using water. The caffeine is then washed from the column using methanol, leaving the fats and other nonpolar substances on the column.

weighing by difference

Is a method used to accurately weigh the amount of material transferred. The mass of a container before (with dry material) and after transferring the material is taken and the difference between these values is the mass of material transferred. necessary for hygroscopic reagents

measuring pipet

Is graduated and can be used to measure various volumes of liquid accurately

Molarity vs. Molality (Temperature change)

Molarity changes as temperature changes because it is a unit of moles per volume. However, molality is a unit of moles per mass which remains unchanged

ppb

Parts Per Billion. A Unit Used To Express The Concentration In A Solution.

ppm

Parts per million - measuring system for the amount of substance present.

What types of columns are used with gas-solid chromatography?

Porous layer open tubular columns

preconcentration

Process of concentrating trace components of a mixture prior to their analysis.

The chemist collects a representative sample of the very fine, uniform stamp sands near the town. What is the chemist's next step?

Remove or mask any interfering substances.

ashless filter paper

Specially treated paper that leaves a negligible residue after ignition of a precipitate. It is used for gravimetric analysis.

solvent trapping

Splitless gas chromatography injection technique in which solvent is condensed about 15 degrees celsius below its boiling point at the start of the column. - leads to sharp chromatographic peaks entire solute dissolve in a narrow band in the condensed solvent.

analyte

Substance being analyzed

experimental error

The difference between the true value of a measurement and the measured value

The real rule

The first digit of the absolute uncertainty is the last significant digit in the answer.

Denby and Scott used an organic solvent to extract fats from the crude sample before extracting the caffeine and theobromine from the chocolate sample in hot water. In the solid-phase extraction, the crude sample is extracted with hot water first. Then the fats are extracted from this aqueous extract using an organic solvent.

The method used by Denby and Scott used petroleum ether, an organic solvent, to remove fats from the crude sample before using hot water to extract the caffeine and theobromine. In the solid-phase extraction, caffeine and theobromine are first extracted using hot water. The aqueous sample is then applied to a silica column and the fats remain adhered to the disposable column throughout the procedure.

formal concentration

The molarity of a substance if it did not change its chemical form on being dissolved. It represents the total number of moles of substance dissolved in a liter of solution, regardless of any reactions that take place when the solute is dissolved. Also called analytical concentration or formality.

light as a wave

The product of the frequency and wavelength of a wave of light is the speed of light. Frequency is the number of oscillations that a wave makes each second. The speed of light in a vacuum is 2.998 × 108 m/s. Light travels slower through matter than through a vacuum.

storing samples

The sample composition may change with time after collection because of chemical changes, reaction with air, or interaction of the sample with its container. Glass is a notorious ion exchanger that alters the concentrations of trace ions and proteins in solution. Plastic containers must be washed before use. Polyethylene containers can contribute a measurable flux of analyte even after being soaked in acid for several months.

Why is it more difficult to provide an accurate analysis of the caffeine content of a chocolate bar containing macadamia nuts than a pure chocolate bar?

The sampling strategy is more complex for the heterogeneous material than for the homogeneous material.

Example of sample preparation

The students are frustrated when their sample is cloudy after repeated extractions, centrifugations, and filtrations.

mean

The sum of measured values divided by the number of measurements. aka the average or the center of the distribution

Another pair of students repeated the analysis of caffeine in chocolate bars performed by Denby and Scott to verify their results. However, they were in a hurry and after extracting the fat, they performed only one aqueous wash and transfer of the fat-free chocolate residue. Predict how their results will compare to those of Denby and Scott.

Their data will likely show a lower caffeine content because they did not completely transfer all of the fat-free chocolate residue. These students likely did not make a quantitative transfer of the fat-free chocolate residue because they performed only one rinse and transfer, so the amount of caffeine in their final sample is likely less than if they would have repeated these steps multiple times to ensure the complete transfer of the residue.

The temperature program for a separation starts at a temperature of 50 degrees Celsius and ramps the temperature up to 270 degrees Celsius at a rate of 10 degrees celsius/min.

Weakly retained solutes will separate and elute early in the separation. Strongly retained solutes will remain at the head of the column when the temperature is low. At 10 degrees Celsius /min, a total of 22 min are needed to reach 270 degrees Celsius. The vapor pressure of strongly retained solutes will increase as the temperature increases.

aqua regia solution

a 3:1 (vol/vol) mixture of HCl and NHO3 used to dissolved Au and Pt (these strong oxidizing agents can dissolve difficult substances)

dessicator

a closed chamber containing a drying agent

outlier

a datum far from other points

open tubular column

a hollow capillary tube with inner walls that are coated with stationary phase material

Gas Chromatography

a method of separating chemicals to establish their quantities mobile phase: gas stationary phase: usually a nonvolatile liquid like polymer but sometimes a solid analyte: gas or volatile liquid

buret

a precisely manufactured glass tube with graduations enabling you to measure the volume of liquid delivered through the stopcock (the valve) at the bottom. (0 mL marker is at the top) interpolate the reading to 0.01 mL

derivatization

a procedure in which analyte is chemically modified to make it easier to detect or separate.

Temperature programming

a procedure used in gas chromatography in which the temperature of the column is raised during the separation to increase analyte vapor pressure and decrease retention times of late-eluting components.

absorption

a process in which one substance is taken inside another (example: water absorbs into the sponge)

tris

a pure compound that measures concentrations of acids as a primary standard

excess reagent

a reagent present in a quantity that is more than sufficient to react with a limiting reagent; any reactant that remains after the limiting reagent is used up in a chemical reaction

High pressure asher

a resistive heating element inside a chamber for digestion at temperatures up to 270 under a pressure of 140 barr.

ambient temperature

a sample reaches this particular temperature when it is equal to the temperature of the surroundings

green chemistry

a set of principles intended to change our behavior to help sustain a habitable planet

Student's t

a statistical tool used most frequently to express confidence intervals and to compare results from different experiments

method of least squares

a statistical way to find the best-fitting line through a set of data points. y=mx+b

a low pka means

a strong acid

electrolyte

a substance that dissociates into ions in solution. (strong or weak)

coprecipitation

a substance whose solubility is not exceeded precipitates along with another substance whose solubility is exceeded

primary standard

a weighed amount of pure reagent in a known volume of solution. pure enough to be weighed and used directly. (greater than 99.9%) should not decompose under ordinary storage stable when dried by heat or vacuum Examples: CaCO3, AgNO3, Ni(metal)

relative uncertainty

absolute uncertainty/magnitude of measurement . can be reduced by increasing volume delivered by the buret.

cloud point extraction

accomplishes a liquid-liquid extraction plus preconcentration of analyte by use of a surfactant that forms spherical micelles (Box 26-1) into which analyte is extracted

What is the purpose of a guard column?

accumulate nonvolatile substances that would otherwise contaminate the chromatography column and degrade its performance

The first 3- to 10-m length of a capillary column serves as a guard column and retention gap. Guard columns

accumulate nonvolatile substances to prevent column contamination.

standard mass

affected by buoyancy, ways less in air than in a vacuum

cold trapping

an alternative means of condensing solutes in a narrow band at the beginning of the column by using an initial column temperature at least 100°C lower than the boiling point of the solutes of interest

steel needles

an avoidable source of metal contaminatio n

metal chelating agent

an ion or molecule that binds with a metal to allow transfer into another phase

linear range

analyte concentration range over which response is proportional to concentration

gas-solid adsorption chromatography

analyte is adsorbed directly on solid particles of stationary phase

extraction

analyte is dissolved in a solvent that does not necessarily dissolve the entire sample and does not decompose the analyte

species

any chemical of interest

limiting reagent

any reactant that is used up first in a chemical reaction; it determines the amount of product that can be formed in the reaction

eratic readings

balance door open, object hot or cold, static charge on object

symptoms of excessive column bleeding

base line high or rising at lower temperatures than normal increasing broadening and tailing with successive injections changing retention times in successive injections

on column injection

best injection method for quantitative work and thermally sensitive compounds. injected directly into the column liner without going through a hot injector. limited to clean samples containing little to no nonvolatile components

gross error

blunders. aka. extreme instances of random or systematic error due to departures from procedure unrecoverable errors

transfer pipet

calibrated to deliver one fixed volume

static charge

can be dissipated by patting balance and object with antistatic brush

Random sample

collected by taking portions from an appropriate number of segments chosen at random

Derived units

combinations of SI base units examples: Force (N), heat (J) , and Pascal (Pa)

quantitative transfer

complete transfer

reliability

consistency of measurement

standard solutions

contain known concentrations of analyte

When extracting a sample with a liquid, the liquid is __________ from the sample.

decanted

raising column temperature

decreases retention time and sharpens peaks

micropipets

deliver volumes from 0 to 1,000 microliters. require repeated calibration and maintenance.

agate mortar

designed for grinding small particles into fine powder

anhydrous

destitute of (without) water

random heterogeneous material

differences in composition occur randomly and on a fine scale

linear velocity

distance per unit time traveled by solvent

composite sample

draws from each region, and the number of samples from each region is proportional to the area of the region

Silanization

end capping. used by column manufacturers to reduce tailing by blocking the silanol groups with nonpolar (SiOH) groups

matrix

everything in the unknown other than the analyte . may cause systematic error thus it is crucial to know what is in the sample

liquid - liquid extraction

extract nonvolatile analyte, typically from an aqueous solution into an organic solvent. The vapors condense into the extraction vessel. Passing through the liquid, analyte is extracted and passes to the solvent reservoir where it is increasingly concentrated as extractions continue

packed column

filled with particles of stationary phase

eluent

fluid entering the column

eluate

fluid exiting the column

adjusted retention time

for a retained solute is the additional time required to travel the length of the column, beyond that required by solvent

retention time

for each component is the time that elapses between injection of the mixture onto the column and the arrival of that component at the detector

Under what condition is on column injection used?

for samples that decompose above their boiling point

headspace

gas phase above a solid or liquid in a sealed container

carrier gas

gaseous mobile phase in GC

reverse pipetting

good for methanol and hexane. a technique for micropipettes

accuracy

how close a measurement is to the true value

ion pair extraction

hydrophobic cations and anions bring ions of opposite charge from aqueous phase into an immiscible organic solvent.

reading drifts up

hygroscopic material absorbing moisture from the air

aqua regia

if a non-oxidizing agent is insufficient, these oxidizing acids are used to dissolve inorganic materials

causes of excessive column bleed

include excessive column temperature, oxygen from leaking septum or fitting, oxygen contamination from carrier gas, injection of chemicals that react with the stationary phase.

increasing inlet pressure

increases the flow of the mobile phase and decreases retention time.

antilogarithm

inverse of the logarithm

retention volume

is the volume of mobile phase required to elute a particular solute from the column

what is the main source of uncertainty for most elements ?

isotopic variations in different measurements

segregated heterogeneous material

large regions have obviously different compositions

plate height

length of column required for one equilibration of solute between the mobile and stationary phases.

metal chelation extraction

ligand + metal to allow transfer into the organic phase

reading drifts down

liquid evaporating

mother liquor

liquid from which a substance precipitates or crystallizes

filtrate

liquid that passes through the filter

below the optimum linear velocity

longitudinal diffusion broadening becomes dominant

temperature limits of gas chromatography

lower limit: it is the temperature at which the stationary phase no longer behaves like a liquid

open tubular column

made of fused silica with an exterior coating of polyimide (a plastic capable of withstanding ) for support and protection from atmospheric moisture. offer higher resolution, shorter analysis time, and greater sensitivity than packed columns, but they have less sample capacity.

absolute uncertainty

margin of uncertainty associated with a measurement (with units)

Which is measured more precisely? Mass or volume?

mass

true mass

mass measured in a vacuum (buoyancy)

sampling constant

mass of sample that will produce a relative sample standard deviation of 1%.

tare

mass of the empty vessel

above the optimum linear velocity

mass transfer broadening becomes dominant

Linearity error

maximum error of a balance that can occur as a result of non-linear balance response

linear response

means that peak area is proportional to analyte concentration. For very narrow peaks, peak height is often substituted for peak area.

standard deviation

measure of reproducibility

standard deviation of the mean

measures uncertainty of the mean. equals the standard deviation divided by the square root of the sample size. also called standard uncertainty

fusion

melting. substances may be dissolved in hot, molten inorganix flux. carried out in a Pt-Au crucible. large amount of impurities may be introduced due to the large amount of solid reagent.

SI base units

meter, kilogram, second, kelvin, mole, ampere, candela

Chemical analysis

middle portion of a process that begins with a question and ends with a conclusion.

solute vs. solvent

minor species vs. major species

Strong electrolyte

mostly dissociated into ions in solution

laboratory sample

must have the same composition as the bulk sample and the individual aliquots are then used for analysis.

degrees of freedom

n-1.

to improve resolution:

narrower column longer column different stationary phase

dry ashing

no liquid used - halogens in coal -metals in plant material

pyrolysis

nonvolatile samples are heated to temperatures that cause thermal decomposition. The resulting gas is transferred to the gas chromatography.

weak electrolyte

partially dissociated into ions in solution

standard test sieves

particles can be sorted by passing them through a series of mesh sieves. particle diameter range varies with each sieve

grinding

performed in a mortar and pestle

chromatogram

plot of detector response versus retention time

aliquots

portions

decant

pour off gently

Under what condition is split injection used?

preferred for samples where the analytes of interest constitute >0.1% of the sample.

Under what condition is splitless injection used ?

preferred for trace analysis of analytes that are less than parts-per-million in the sample.

blank solutions

prepared with the same reagents and solvents as standard solutions and unknowns but there is no desired analyte added. Are there impurities or interfering species in the solution?

elution

process of passing a liquid or a gas through a chromatography column

QuEChERS

quick, easy, cheap, effective, rugged and safe sample preparation procedure used in analytical chemistry. First the analyte is extracted, followed by sample cleanup to remove matrix components before chromatography.

indeterminate error

random error. arises from uncontrolled variables in measurement. equal chance of being positive and negative. Always present, cannot be eliminated. Might be reduced with better technique. Ex: subjective reading of a scale, electrical noise in an instrument.

retention index

relates the retention time of a solute to the retention times of linear alkanes and provides a scale of relative retention that remains constant for all columns with the same stationary phase

Clausius-Clapeyron equation

relates the vapor pressure of a substance at different temperatures to its heat of vaporization

Gaussian distribution

represents a set of experimental data that is normally distributed. Repeated experiments approaches this sort of distribution. Known as "normal distribution" characterized by the average and the standard deviation

splitless injection

required for very dilute samples. also requires solvent trapping or cold trapping. Temperature programming is also necessary.

universal detector

responds to all analytes but not to carrier gas

selective detector

responds to limited classes of analytes

septum

rubber disk in which a sample is injected through for gas chromatography

the field consists of several different regions, areas that are covered with grass, areas that are covered with brush and small shrubs, and several small areas with trees growing on them. What term best describes the field, and what type of sample should the laboratory construct?

segregated heterogeneous material and composite sample

size exclusion chromatography

separated by size and sometimes molecular weight

Chromatography

separates analytes and measures the quantity of each compound. (based on polarity) analytes are able to absorb uv radiation from lamp.

calibration curve

shows the response of a chemical analysis to known quantities (standard solutions) of analyte. less certainty in y

readability

smallest increment of mass that can be indicated

What is the equation for calculating the overall variance?

so^2=sa^2 + ss^2

SPE

solid phase extraction. removes sugars, fats, and fine particles all on one small column.

affinity chromatography

solute binds to a molecule specific for the solute

partition chromatography

solute equilibrates between mobile phase and film of liquid attached to stationary phase

ion exchange chromatography

solute ions of the opposite charge are attracted to the stationary phase

interference

species other than the analyte decreases or increases the response of the analytical method. making it appear that there is more or less analyte present

shatterbox laboratory mill

spins a puck and ring inside a grinding container pulverizing up to 100 g of material.

Cold trapping and solvent trapping are used with ________ injection to give _________ peaks.

splitless;sharper

Calibration curve

standard curve, measures detector response for known concentration of each analyte. Peak height versus concentration

relative standard deviation

standard deviation expressed as a percentage of the mean value. aka coefficient of variation

Trouton's Rule

states that the heat of vaporization is proportional to the atmospheric-pressure boiling temperature near 88 j/mol * K

gas liquid partition chromatography

stationary phase is a nonvolatile liquid bonded to the inside of the column or to a fine solid support

determinants

summarize arithmetic operations. Used in the least square method to express the final solution for slope and intercept

slurry

suspension of a solid into a liquid

aerosol

suspension of fine liquid droplets or solid particles in the gas phase

determinate error

systematic error. arises from a flaw in equipment or experimental design. can be discovered and corrected

Selected Reaction Monitoring (SRM)

technique in which a precursor ion selected by one mass separator passes through a collision cell in which the precursor breaks into several fragment ions. A second separator then selects one of these ions for detection

gravimetric analysis

the MASS of product from a reaction is measured to determine how much unknown was present

slope

the change in y over the change in x. equals 'm' in the equation of the line

molality

the concentration of a solution expressed in moles of solute per kilogram of solvent

dynamic range

the concentration range over which there is a measurable response to analyte, even if the response is not linear

mantissa

the decimal part of a log

vertical deviation

the difference between the y value of a data point and the y value of the least squares curve for the same x value.

desiccant

the drying agent . example : 98% wt sulfuric acid

parallax

the error that occurs when your eye is not at the same height as the liquid

precision

the exactness of a measurement

Chromatogram

the graph of detector response versus time confirm identity of individual peaks by: spectral characteristics, spike with verified caffeine solution to see if one peak grows)

ignition

the heating to high temperature of some gravimetric precipitates to convert them into a known, constant composition that can be weighed. Usually over a burner or in a furnace

characteristic

the integer of a log

supernatant

the liquid above the packed solid

extraction

the physical transfer of a solute from one phase to another

adsorption

the process in which a substance sticks to a surface

calibration

the process of measuring the actual quantity that corresponds to an indicated quantity on the scale of an instrument.

serial dilution

the process of successive solutions to reach a desired concentration of reagent

analysis may be meaningless if

the sample was collected improperly, measures to ensure reliability were not performed, or the results weren't communicated clearly

sample preparation

the series of steps required to transform a sample so that it is suitable for analysis. (dissolving the sample, extracting analyte from matrix, concentrating dilute analyte, chemical conversion, mask interfering species)

The larger the transfer pipet ..

the smaller the relative uncertainty

variance

the square of the standard deviation

null hypothesis

the statement that two sets of data are drawn from populations with the same properties such as standard deviation ( F test) or mean ( T test)

Formula mass

the sum of the average atomic masses of all atoms represented in its formula or the molecular mass of a strong electrolyte

variance of an analysis

the sum of the sampling variance and the analytical variance

masking

the transformation of an interfering species into a form that is not detected

standard deviation

the width of the distribution . How closely are the data gathered about the mean?

Fcalc>Ftest

there is a significant difference between the population standard deviations of the two populations.

What is the purpose of a serial dilution?

to transfer accurately small amounts of material that are too little to weigh accurately.

lot

total material from which samples are taken

True or false? Many small extractions are more effective than a few large extractions

true

True or false? in Gas chromatography solutes equilibrate between the stationary and vapor phases.

true

split injection

used for relatively concentrated samples. Only 0.2-2.0% of the sample is delivered to the column and the remaining flows to waste, Injection of the entire sample could overload the column. (use packed liner)

confidence interval

used to compare mean values measured by different methods. compared measured result to a "known" calue

acid washing

used to replace H+ to surfaces with low cation concentrations

supercritical fluid extraction

uses a supercritical fluid as the extraction solvent.

Ball mill

uses steel or ceramic balls rotated inside a drum to crush sample into a fine powder

As the temperature of the GC column increases, the ______ of the analyte increases, the retention time _____, and the peak shape _____ .

vapor pressure; decreases; sharpens

gas chromatograph

volatile liquid or gaseous sample is injected through a septum (a rubber disk) into a heated port, in which it rapidly evaporates.

volume percent

volume of solute/volume of solution

flow rate , F

volume of solvent per unit time traveling through column

a strong acid has

weak conjugate base and a low pKa.

spiking

when an authentic compound is added to the unknown. The most reliable way to compare retention times

y-intercept

where a line crosses the y-axis, x=0, b in the equation of the line

general elution problem

which is the inability of a single isothermal column temperature to provide adequate separation within reasonable time for samples containing compounds with very different boiling points.

abscissa

x-axis of a coordinate graph

ordinate

y-axis of a coordinate graph