# achem

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1. sampling
is collecting a small amount of material which will be chemically analyzed. should be representative and homogeneous
is the conversion of a substance into a form which is not detected in a particular type of analysis
3. mass percent
mass solute/mass solution
4. Volume percent
volume solute/volume solution
5. Mass/volume percent
mass of the solute divided by the volume of solution
6. parts per million
1mg solute/ 1000 g solution =1X10-6

aqueous solutions = 1 mg per 1 L of solution since solution density is often very lose to 1.0 g / mL
7. parts per billion
1 microg solute per L solution.
8. Parts per trillion
1 ng (10-9 g) solute per L solution.
9. Molality
moles solute/ mass solvent [mol/kg]

independent of temperature
10. equilibrium constant
aA + bB -> cC +dD

K=[C]c[D]d/[A]a[B]b

• when K is large, there are more products
• when K is small, there are more reactants
• Solutes must be in M, gases are in bars, pure components are equal to 1
• True equlibrium constants are expressed in terms of activity: a=[A]gammaa

• K for reversed reactions = 1/K
• Multiplying reactants by C then K= K^C
11. reaction quotient
useful tool to determine which way equilibrium will shift. same equation as K but uses initial concentrations present in reaction

• Q>K shift towards reactants
• Q<K shift towards products
• Q=K equilibrium
12. Precision
• reproducibility of a result; can be measured by:
• -standard devation
• -mean deviation from the mean
• -range
• -relative standard dev
13. Accuracy
• -how close a measured result is to a true value
• -quantitatively described by absolute error (xi-xtrue) and relative error (xi-xtrue)/xtrue *100
14. random (indeterminate) error
results from human error- physical limitations. they do not affect the mean of the data set
15. Systematic error (determinate error)
results from faulty equipment so error continues to be repeated. shifts entire data set
16. confidence interval
a range of values within which there is a specified probability of finding the true population mean.
17. t-test
if tcalc > ttable they are statistically different

ttable is with N1+N2-2 DOF
18. Q-test
determines if a data point is an outlier. Qcalc>Qtable , its an outlier

Qcalc= gap/range
19. Blank
solution that contains all components of a sample except an analyte
20. sample matrix
all components of the sample excluding the analyte
21. spike
a known amount of the analyte which is added to a sample
22. sensitivity
the slope of the calibration curve. measurement how large a detector response is recorded per unit analyte concentration
23. selectivity
being able to distinguish between an analyte signal and another species in the solution
24. detection limit
the lowest concentration of the analyte that can be reliably detected; produces a signal 3 std dev. of the measurements. minimum detectable concentration= 3s/m. ydl=yblank+3s
25. common ion effect
a salt will be less soluble of one of its constituent ions is already present in the solution
26. quantitation limit
• -the lowest analyte concentration that can be reliably quantified
• -produces a signal 10sigma of the blank noise
• =10s/m
27. external calibration
uses external means to creat a calibration curve. compare detector signal for sample with calibration curve
28. internal calibration- method of standard additions
• -use when the sample matrix is complex or unknown
• -sample is spiked with a series of known amounts of analyte and the resulting change in detector is used the measure the concentration in the origonal sample
• -eliminates matrix effects
29. calibration curve
plot of the detector signal vs concentration

• y=mx+B
• det. sig= m(concentration) + yblank

yblank= mean signal from blank

slope, m, is the sensitivity
30. volumetric analysis
the volume of a known reagent required for a complete reaction with analyte by a known reaction is measured; carried out by titration
31. indicator
a substance which has a physical property that changes when the analyte is used up
32. primary standard (5)
• -should be available in high purity
• -not decompose under storage conditions
• -be stable when dried or heated
• -have relatively high molar mass
• -have no waters of hydration
33. solubility product
an equilibrium constant describing the solubility of a particular substance

AxBy -> xA +yB

Ksp=[A]x[B]y
34. Volhard titration
• -formation of a soluble colored complex at the end point
• -back titration
• 1)Cl- is precipitated by a known excess quantity of AgNO3
• Ag+ +Cl- -> AgCl (s)
• 2) Filter off precipitate AgCl
• 3) Standard KSCN is used to titrate the remaining Ag+. End point is indicated by red color
• Ag+ + SCN -> AgSCN (s)
• Fe3+ +SCN -> FeSCN2+
35. acids
• -increase H3O+; HCl, HBr;
• -proton donor
36. bases
• decrease H3O+; increase OH-
• -proton acceptor
37. Fajans Method
• -

• •Ag+ is slowly added to a solution containing
• an anion (example Cl-).
• It is believed that the precipitate particles carry a surplus negative
• charge prior to the equivalence point.
• After the equivalence point the particles are believed to carry a net
• positive charge.
38. autoproslysis constant
Kw=[H+][OH-]= 1.0 x 10-14
39. pH
= - Log [H3O+]

so
 Author: jehenry ID: 38079 Card Set: achem Updated: 2010-09-29 16:48:21 Tags: achem Folders: Description: achem Show Answers: