chem 351 exam 1

quantitative chemical analysis

measurements of how much a chemical substance is present; analysis provides a numeric answer

qualitative chemical analysis

identification of what chemical constituents are preset in a substance; test confirms the identity of the compound

sampling

procuring a representative sample to measure

heterogeneous

material composition differs from region to region

homogeneous

material composition is the same everywhere

analyte

substance that is measured

measurand

the quantity of the analyte to be measured

quantitative transfer

transfer of a sample from one container to another such that none is lost; residue is not transferred will result in final analysis error

calibration (standard) curve

a graph of detector response as a function of analyte concentration

method validation

proves suitability of instrument and method

general steps in analytical process

1. formulating the question

2. selecting the analytical procedure

3. samplig

4. preparing the sample

5. validating the method

6. analyzing

7. reporting and interpreting

8. drawing conclusions

formulating the question

translate general questions into specific questions related to chemical measurement

selecting the analytical procedure

search chemical literature to find an appropriate procedure or devise a new procedure

sampling

select representative material to analyze

preparing the sample

convert a representative sample into a form suitable for analysis

validating the method

check that a method reliably produces results that can answer the initial question

analyzing

measure the concentration of the analyte in several identical aliquots; the uncertainty. of the measurement is as important as the measurement itself; replicating measurements are essential

aliquots

portions

reporting and interpreting

deliver a clearly written, complete report of results, highlighting any limitations; be sure the report is appropriate for the intended audience; clearly written reports limit the chance for misinterpretation by those who use them

drawing conclusions

at times, the conclusions may point you toward starting over and reformulating the question

species

any element, compound, or ion of interest; analyte

interference

phenomenon in which the presence of one substance changes the response in the analysis of another substance

matrix

all substances found within a material

masking

process of adding a chemical substance to a sample to prevent one or more components from interfering in a chemical analysis

random heterogenous aterial

differences in composiiton occur randomly and on a fine scale

random sample

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

segregate heterogeneous material

large regions have obviously different compositions

composite sample

made of portions of each region, with relative amounts proportional to the size of the region