ch 1-5 key terms

characterization analysis

What are the sample’s (analytes) chemical and physical properties?

fundamental analysis

How does this method work and how can it be improved?

qualitative anaylsis

need to identify what is present in a sample

(is a particular analyte present)

quantitative analysis

How much (analyte) is present?

SI Units

International System of Units, are the global standard for measurement, forming the modern metric system

scientific notation

a system for writing very large or very small numbers concisely by expressing them as a number between 1 and 10 multiplied by a power of 10

significant figures

convey information about a measurements magnitude and uncertainty (# digits known exactly + one uncertain)

concentration

general measurement unit that reports amount of solute present in known amount of solution

molarity

concentration of a particular chemical species

formality

substances total concentation without regard to its specific chemical form

normality

defines concentration in terms of an equivalent, which is the amount of one chemical species that reacts stoichiometrically with another chemical species

molality

used in thermodynamic calculations where a temp independent unit of concentration is needed

weight percent, volume percent, weight to volume percent

express concentration as the units of solute present in 100 units of solution

parts per million and parts per billion

ratios that give the grams of solute in, respectively, one million or one billion grams of sample

p-function

concentration that spans many orders of magnitiude

p function of X is pX

pX= -log(X)

analytical balance

measures an objects mass (digital)

graduated cylinder

simplest device for delivering known volume of liquid reagent

volumetric pipet

more accurate method for delivering known volume of solution

volumetric flask

contains specific volume of solution (calibration mark)

meniscus

liquids top surface curve

bottom should align with calibration mark

desiccator

a closed container that isolates the sample from the atmosphere

desiccant

drying agent placed at bottom of desiccantor

stock solution

prepared by weighing out appropriate portion of pure solid

a solution containing a predetermined amount of dyestuff dissolved in a specified quantity of water

quantitative transfer

to ensure complete transfer, rinse the beaker several times with a little water adding each rinse to the volumetric flask

dilution

the process of decreasing the concentration of a solute in a solution by adding more solvent, typically water, without changing the amount of solute present

chemical analysis

any chmical or physical principle that we can use to study an analyte

method

the application of a technique for a specific analyte in a specific matrix

procedure

set of written directions that tell us how to apply a method to a particular sample

protocol

a set of stringent guidelines that specify a procedure that an analyst must follow if an agency is to accept the results

mean

X with line on top

numerical average for a data set

median

X squiggly line over top

middle value when we order our data from smallest to largest

range

W

the difference between a data sets largest and smallest values

standard deviation

s

the spread of individual values about their mean

variance

the square of the standard deviation

determinate error

error that affects the accuracy of an analysis

sampling error

sampling strategy does not provide us with a representative sample

method errror

exists when the value for kA or for Smb is in error

measurement error/tolerance

10mL volumetric pipet has a tolerance of ± 0.02 mL

so its range is 9.98-10.02 mL

personal error

ex: ability to see a change in color of an indicator that signals endpoint of titration

constant determinate error

magnitude is the same for all samples (more significant when anaylzing smaller samples)

proportional determinate errror

the errors magnitude depends on the amount of sample (more difficult to detect)

standard reference material

standards from the National Institue of Standards and Technology

repeatability

the precision when a single analyst completes an analysis in a single session using the same solutions, equipment, and instrumentation

reproducibility

precision under any other set of conditions

indeterminate errors

errors that affect precision - characterized by random variations in their magnitude and direction

error

the difference between a single measurement or result and its expected value

bias

erorr is a measurement of bias

uncertainty

the range of possible values for a measurement or result

propogation of uncertainty

allows us to estimate the uncertainty in a result from the uncertainties in the measurements used to calculate that result

population

set of all objects in the system we’re investigating

sample

limited subset (sample) of population

probability distributions

specific result as a function of the possible results

binomial distribution

population in which the result is # of times an event occurs during a fixed number of trials

normal distribution

gaussian distribution (most common)

confidence intervals

how confident we are in assigning the range

standard error of the mean

the standard deviation of the mean

histogram

sample divided int ointervals by mass

central limit theorem

measurement is subject to a variety of indeterminate errors

degrees of freedom

number of independent measurements

significance test

determines whether the difference between two or more results is sufficiently large that it cannot be explained by indeterminate errors

null hypothesis

H0 indeterminate errors are sufficient to explain any differences between our results

alternative hypothesis

HA the differences in our results are too great to be explained by random error

two-tailed significance test

each shaded area account for 2.5% of the area under the probability distribution curve

total 5%

one-tailed significance test

shaded area represents 5%

type 1 error

When we conduct a significance test at a = 0.05, there is a 5% probability that we will incorrectly reject the null hypothesis

type 2 erorr

occurs when we retain a null hypothesis even though it is false

t-test

samples confidence interval is smaller than explained by indeterminate error and we retain the null hypothesis

F test

evaluate whether a difference between s2 and o2 is significant

unpaired data

Measurements from two independent samples that are compared using t test

paired data

measurements made on the same individual or sample under different conditions

paired t-test

We retain the null hypothesis if texp is less than or equal to t(a, o)

outlier

measurement that is not consistent with other measurements

dixons q test

The null hypothesis is that there are no outliers, and the alternative hypothesis is that there is an outlier

grubbs test

distance between the samples mean and the potential outlier

chauvenets criterion

we can reject the data point if the pobability of obtaining the data points value is less than (2n)-1

detection limit

the smallest concentration or absolute amount of analyte that has a signal significantly larger than the signal from a suitable blank

limit of identification

the analytes signal at the limit of identification

Kernel density plot

a smoothed histogram

box plot

useful way to identify potential outliers without making any assumptions about the datas distribution

primary standard

reagent that we can use to dispense an accurately known amount of analyte

secondary standards

reagents that do not meet the criteria of primary standards

reagent grade

chemicals of a high purity level suitable for laboratory, analytical, and research purposes, often meeting or exceeding the standards set

serial dilution

most concentrated standard diluted then that is diluted etc

single point standardization

a calibration method in analytical chemistry where the concentration of an unknown sample is determined by comparing its signal to that of a single standard solution of known concentration

multiple point standardization

should include at least 3 standards

calibration curve

a plot of Sstd versus Cstd

external standards

prepared and analyzed separate from the samples

matrix matching

trying to match the standards matrix to that of the sample

method of standard additions

carrying out the standardization in the sample

internal standard

species added to all samples and standards

linear regression

goal; to determine the best estimate for B0 and B1

unweighted linear regression

each standard contributes equally in our estimate of the slope and y intercept

residual error

the difference between y and y^ for each value of x

standard deviation about the regression

the cumulative deviation of our data from the regression line (total residual error) is proportional to the uncertainty in the regression

weighted linear regression

each xy pairs contribution to the regression line is inversely proportional to the precision of yi

total youden blank

the true blank correction