chem 251 CSULB final terms and procedures ch 1-9

the analytical process

1. state the problem

2. translate the problem into a scientific question

3. design the analysis to answer the scientific question

4. translate the numerical answer into the decision

qualitative analysis

what is present?

quantitate analysis

how much is present

what different methods are there in analytical chemistry

classical and instrumental

when selecting a procedure what should you take into consideration?

availability, suitability, and interference

homogeneous

composition is the same throughout

heterogeneous

composition differs from place to place

qualitative analysis tells you:

what is present in the sample

the correct order of chemical analysis is:

1. select the procedure

2. choose a method

3. collect the sample

4. analyze the sample

5. report the results

true or false ?

false

when you select the procedure you need to consider (choose all that apply)

a. sensitivity

b. availability

c. possible interferences

a,b,c

the aliquot is?

a portion of a sample taken for chemical analysis

the chemical concentration can be expressed in units of ( select all that apply):

a. mol/kelvin

b. mol/L

c. parts per million

b,c

the statistical data analysis is:

part if the analytical process that helps evaluate the validity of collected data.

what are two types of basic errors you need to focus on for statistical data analysis?

1.systematic error

2. random error

what is systematic error?

a problem with the method, all errors are of the same size magnitude and direction.

what is random error?

based on limits and precision of a measurement.

can a systematic error be fixed?

yes using problem solving skills and chemical /physical knowledge.

what is the most common type of error in analytical chemistry?

random error

random error can be treated ___________

statistically

for gaussian distribution the average value is found.

in the middle of the the highest peak.

the width of the gaussian distribution graph gives us:

the random error associated

standard deviation is a:

measure of the width of the distribution

confidence interval is:

the range of values with which there is a specific probability of finding the true mean.

statistical t-test is :

any statistical hypothesis test in which the test statistic follows a a students t-distribution under the null hypothesis

the t-test tells:

tells you how significant the differences are between the groups are

if Tcalculated is greater than T(table) are the means same or different?

they are different at the confidence interval.

grubbs test is:

a test used to detect in a univariate data set assumed to come from a normally distributed population.

grubbs test is used to:

detect if an outlier belongs to the data set.

if G(calculated) is greater than the G(table) the point should be?

rejected.

normal distribution is useful for analyzing:

random errors

uncertainty is expressed as:

standard deviation or confidence interval

the least square method finds:

the best straight line through data points. in this method we minimize the squares of vertical deviation.

random error is also called:

indeterminate error

systematic error is also called

determinate error

precision cjfaq1

a measure of the reproducibility of the result.

accuracy

is how close a measured value is to the true value.

accuracy is defined as the _________ to the true value

nearness

absolute uncertainty

expresses the margin of uncertainty associated with a measurement.

relative uncertainty

compares absolute uncertainty with its associated measurement.

standard solution

a solution containing a known quantity of analyte or reagent

calibration curve

is a graph showing how the experimentally measured property depends on the concentrations of the standards.

if T(table) is > T(calc)

values are not different and belong to the same distribution

endpoint

a marking by a sudden change in physical property of the solution.

primary standard

a reagent that is pure enough to weigh out and directly provide a known number of moles.

back titration

a known excess of a standard reagent is added to the ana

solubility product (Ksp)

is the equilibrium constant for the reaction in which a solid salt (ionic compound) dissolves to give its constituent ions in solution.

saturated

a solution that contains all the solid capable of being dissolved

volhard titration

formation of a soluble, colored complex at the endpoint.

Fajans titration

adsorption of a colored indicator on the precipitate at the endpoint.

gravimetric analysis

the mass of a product is used to calculate the quantity of original analyte

combustion analysis

a sample is burned in excess oxygen and the products are measured.

colloids

particles with diameters in the approximate range 1-500 nm.

nucleation

dissolved moleciules or ions form small crystaline aggregate capable of growing into large particles

particle growth

solute molecules or ions add to an existing aggregate to form a crystal.

adsorption

penetration beyond the surface, to the inside.

masking agent

when impurities are masked which prevent them from reacting with the precipitant.

bronsted and lowry

acid is a proton donor and base is a proton acceptor.

salt

any ionic solid

autoprotolysis

one substance as both an acid and a base. (H2O)

pH =

-log[H+]

Ka

acid dissociation constant (Ka= [H+][A-]/[HA])

Kb

base hydrolysis constant ([BH+][OH-]/[B])

Ka xKb =

Kw = ([H][OH-])

buffer

consists of a mixture of a weak acid and its conjugate base.

a buffer resists the change in pH

because the buffer consumes the added acid or base

indicator

an acid or base whose various protonated species have different colors.

absolute uncertainty

expresses the margin of uncertainty associated with a measurement.

relative uncertainty

compares absolute uncertainty with its associated measurement.