achem

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

mass solute/mass solution

volume solute/volume solution

mass of the solute divided by the volume of solution

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

1 microg solute per L solution.

1 ng (10-9 g) solute per L solution.

moles solute/ mass solvent [mol/kg]

independent of temperature

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
• Adding reactions= K1*K2
• Multiplying reactants by C then K= K^C

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

• reproducibility of a result; can be measured by:
• -standard devation
• -mean deviation from the mean
• -range
• -relative standard dev

• -how close a measured result is to a true value
• -quantitatively described by absolute error (xi-x_true) and relative error (xi-x_true)/x_true *100

results from human error- physical limitations. they do not affect the mean of the data set

results from faulty equipment so error continues to be repeated. shifts entire data set

a range of values within which there is a specified probability of finding the true population mean.

if t_calc > t_table they are statistically different

ttable is with N₁+N₂-2 DOF

determines if a data point is an outlier. Qcalc>Qtable , its an outlier

Qcalc= gap/range

solution that contains all components of a sample except an analyte

all components of the sample excluding the analyte

a known amount of the analyte which is added to a sample

the slope of the calibration curve. measurement how large a detector response is recorded per unit analyte concentration

being able to distinguish between an analyte signal and another species in the solution

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. y_dl=y_blank+3s

a salt will be less soluble of one of its constituent ions is already present in the solution

• -the lowest analyte concentration that can be reliably quantified
• -produces a signal 10sigma of the blank noise
• =10s/m

uses external means to creat a calibration curve. compare detector signal for sample with calibration curve

• -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

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

the volume of a known reagent required for a complete reaction with analyte by a known reaction is measured; carried out by titration

a substance which has a physical property that changes when the analyte is used up

• -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

an equilibrium constant describing the solubility of a particular substance

A_xB_y -> xA +yB

K_sp=[A]^x[B]^y

• -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⁺

• -increase H₃O⁺; HCl, HBr;
• -proton donor

• decrease H3O+; increase OH-
• -proton acceptor

• -uses an adsorption indicator
• -

• •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.

Kw=[H+][OH-]= 1.0 x 10^-14

= - Log [H3O+]

so