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a chem
exam 1
| Question | Answer |
|---|---|
| sample | portion taken for analysis |
| matrix | everything except the analyte |
| analyte | particular substance being measured/studied |
| major component | analyte makes up significant portion of sample (1----> 100%) |
| minor component | substance present at low levels (0.1 ----> 1.0%) |
| trace component | substance present at very low levels (<0.01%) |
| steps in the chemical analysis | 1. identify the problem and find a method of analysis 2. sampling (huge component) 3.sample preperation- converting sample into something suitable for analysis 4. analysis- actually preforming the measurements 5. interpret the results- data analysis |
| sampling aspects: 1. 2. | 1. obtain a representative sample 2. extract a smaller lab sample from bulk sample |
| sample preperation may incclude: | concentration, dilution, chemical rxn of analyte, removing/masking interfering agents---- may do all or none of these methods |
| qualitative analysis | is a particular analyte in the sample? |
| quantitative analysis | how much analyte is present? |
| chemical identification | what is the identify of an unkown chemical in the sample? |
| structural analysis | what is the atomic/molecular mass composition of structure of the analyte? |
| property characterization | what are some chemical/physical properties of the sample? |
| time-dependent analysis | how does the amount of analyte change overtime?----> kinetics |
| an assay of drinking water to determine if the concentration of a particular pollutant is within legal limits is what type(s) of analysis? | quamtitative and qualitative |
| studies to determine the nature of a an unknown toxin in a food sample is what type(s) of analysis? | chemical identification |
| the location of a specific type of protein with in a cell is what type(s) of analysis? | structural analysis |
| often a calibration curve is constructed by plotting the _________ (y-axis) vs. the __________/_____ (x-axis) of the substance analyzed. | response; concentration/amount |
| quantitative transfer | complete transfer of a substance from 1 container to another- example: rinse 3x with solvent |
| reasons for sample preperation include: | 1.analytes are not present in a suitable matrix 2.substances present in the sample interfere with the measurement 3.analyte needs to be in a chemical form that can be studied by the method 4.to get analyte concentration in a suitable level for detection |
| systematic error | determinate error; a repeatable error that can be discovered and corrected----> examples: incorrect calibration of pH meter, blowing out to deliver (T.D.) pipet |
| characteristics of systematic error | 1. occurs on 1 side of the measurement ( consistantly high or low) 2. reproducable 3. predicatable |
| random error | inderterminante error; arises from limitations on the ability to make the physical measurements and natural fluctuations in the quantitiy being measured-----> examples: random electric error, air fluctuations when using a balance |
| random error cannot be __________ and will occur on either side of a measurement | eliminated; may be minimized |
| precision | reproducability of a measurement (st. dev.) |
| accuracy | closeness to the true/accepted value (% error) |
| eliminating all error achieves ___________ | accuracy |
| cannot eliminate random error so there is always a level of __________ | uncertainty |
| absolute uncertainty | margin of error on a measurement; same for all measurements with that device |
| percent relative uncertainty | (absolute uncertainty/measurement)*100 |
| mean | average |
| standard deviation | measure of the dispersion of the numbers from the mean |
| relative standard deviation | (st. dev./average)*100 |
| alpha error | occurs when 2 values are found to be different when they are actually the same- gives false negatives |
| beta error | occurs when 2 values are determined to be the same when they are actually different- gives false positives |
| 1 standard deviation away on a gaussian distribution is | +/- 68.3% |
| 2 standard deviations away on a gaussian distribution is | +/- 95.5% |
| 3 standard deviations away on a gaussian distribution is | +/- 99.95% |
| mu | true value/ given value |
| t | t-table value |
| x-bar | average |
| s | standard deviation |
| s -x-bar | standard deviation/ sqrt of n |
| n | number of trials |
| when developing analytical methods an _______ ________ is often used to establish a baseline response which can later be subtracted from all sample measurements | ideal blank |
| ideal blank | contains everything present (the matrix) EXCEPT the analyte |
| ideal blanks are usually _______ and a ________ blank is used which approximates the ideal blank | impossible; reagent |
| sensitivity | a measure of how the response changes as the amount of analyte is varied- most common way to describe sensitivity is to use the slope of the calibration curve |
| when a method generates a __________ calibration curve, the sensitivity of the method is the same at all concentrations | linear |
| specificity | selectivity; refers to the ability of an analytical method to detect and discriminate between the analyte and another substances in a sample |
| limit of detection (LOD) | 32/m----> s= st. dev. of intercept m =slope |
| limit of quantitation (LOQ) | 10s/m----> s= st. dev. of intercept m= slope |
| linear range and dynamic range | used to refer to calibration curves; ideally methods have large linear ranges since these ranges are well-suited to error propigation and linera regression |
| equivalence point | exact amount of analyte needed to react with titrant |
| end point | marked by some physical change (color, pH, precipitate, etc.) |
| titration error | difference between end point and equivalence point |
| blank titration | estimate of titration error |
| primary standard | compound pure enough to weigh out and determine the exact number of moles |
| hygroscopic | absorbs water from the atmosphere |
| standardization | process of determining exact concetration |
| direct titration | analyte + known titrant ------> product |
| back titration | analyte + known reagent 1 ------> product + excess reagent 1 excess reagent 1 + known reagent 2 -----> product |
| gravimetric titration | use mass not volume; precision improved from 0.3% to 0.1% |
| redox reactions involve the __________ ____ ______ | transfer of e- |
| a molecule is _____________ when it loses electrons | oxidized |
| a molecule is ___________ when is gains electrons | reduced |
| oxidizing agents (oxidants) _______ electrons from another substance | take |
| readucing agents (reductants) ______ electrons to another substance | give |
| electric charge is measured in ______ | coulombs (C) |
| the charge of an electron is | 1.602 x 10 ^-19 C |
| a mole of electrons has a charge of ______________, which is called __________ _________ | 9.649 x 10 ^4 C; faraday's constant (F) |
| electric current (I) | the quantity of charge flowing each second past a point in an electric circuit |
| the unit of current is an ________ (____) | ampere (A) |
| 1 A= | 1C/s |
| work is measured in | joules |
| electric potential | the amount of work that can be done measured between 2 points; measured in volts (V) |
| galvanic cells | batteries; use spontaneous redox reactions to generate electricity; an oxidant and reductant are physically seperated from one another to force the electrons to travel through a wire |
| one line in line notation represents | phase boundary |
| two lines in line notation represents | salt bridge |
| anode in line notation | always on the left |
| cathode in line notation | always on right |
| species in the same phase are seperated by | comma |
| the standard hydrogen electrode is assigned a value of | 0 V |
| a chemical reaction is spontaneous when E^o is | positive |
| E(cell)= | E(cathode) - E(anode) |
| E^o vs. E | E^o is in standard conditions while E is not |
| anode | more negative half-reaction |
| cathode | more positive half-reaction |
| does the cathode loose electrons/mass | yes |
| nernst equation | E = E^o - (0.05916/n) logQ |
| galvanic cells produce electricity becasue they are trying to reach | equilibrium |
| at equilibrium the nernst equation is E^o= | (0.05916/n) log K |
| AglAgCl = | 0.197 V |
| calomel= | 0.241 V |
| S.H.E= | 0 V |
| an indicator can also be used to detect ___________ in titrations | endpoint |
| redox indicators change colors based on __________ state | oxidation |
Created by:
allijeli
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