achem midterm

when are sig.figs significant?

non-zero digits, captive zeros between nonzero numbers, trailing zeros after a decimal point

when are sig figs not significant?

leading zeros

what is the sig fig rule when multiplying or dividing

the result matches the factor with the fewest total sig figs

what is the rule with sig figs when adding or subtracting

the result matches the number with the fewest sig fig decimal places

when do you round to the next even number?

when the digit beyond the last sig fig is exactly 5

what is molarity formula?

n solute / volume of solution in L

what is molarity dependent on?

is temperature dependent because liquid volume changes witg density

what is the mass concentration formula?

m solute over v solution in L

what is molality formula

n solute over m solvent in kg

what is molality dependent on

it is actually independent of temperature because mass doesnt change with temperature

what is mass percent or weight percent

mass solute over mass solution times 100%

what is percent volume

volume solute over volume solution times 100

what mass volume or weight volume

mass solute in g over volume solution in ml times 100

what is parts per million

1 mg of solute over 1 L solution

what is parts per billion

1 microg solute over 1 L solution

what is dilution equation

MconcVconc=MdilVdil

what is dilution equation for mass conc

c conc V conc = c dil V dil

what is dilution equation for mass percent

c conc m conc = c dil m dil

what is density equation

m over V

what is specific gravity equation

d substance over d water

what is percent relative error

%e = e abs divided by measured value times 100

what is the error propagation formula for addition or subtraction

$$e_{y}=\sqrt{e_{x_1}^2 + e_{x_2}^2 + e_{x_3}^2}$$

what is multiplication division error propagation formula

$$\%e_{y}=\sqrt{(\%e_{x_1})^2 + (\%e_{x_2})^2 + (\%e_{x_3})^2}$$

what is a sample

portion of the material selected for analysis

what is matrix

all substances comprising the material except the analyte

what is analyte

the specific substance of interest being measured

what is interference

a species in the matrix that causes an increase or decrease in the detector signal of the analyte

what is masking

transforming an interfering species into an unreactive form so its not detected

what is homogeneous sampling type

uniform composition throughout

what is heterogeneous random sampling type

fine scale random variation, taking random samples

what is heterogeneous segregated sampling type

large segregated patches, take a composite sample proportional to the percent makeup of each region

what goes on the x axis of calibration curves

analyte concentration

what goes on the y axis of calibration curves

detector response

what is the purpose of calibration curves

to measure the response of an unknown to interpolate its exact concentration using y=mx+b

what does qualitative mean

what is present, identification

what does quantitative mean

how much is present , how much is present

what are the steps to chemical analysis

1. formulating the question

2. selecting analytical procedures

3. sampling

4. sample prep

5. chemical analysis

6. reporting and interpret

7. drawing conclusions

what is random type of error

uncontrolled fluctuations with equal chance of being positive or negative

• affects precision

• cant be eliminated but is quantified

what is systemic type of error

flaws in equipment or method design that cause reproducible one directed shifts

• affects accuracy

• can be detected and corrected

what is gross error

major departure from experimental procedure

• leads to outliers

• must be discarded

detecting systematic error

analyzing certified reference materials

• analyzing blank samples

• comparing independent analytical methods

what do you do if G cal is more than G crit

reject the outlier, recalculate the mean and standard deviation without the outlier

what do you do if G calc is less than G crit?

keep the outlier

what do you do if F calc is more than F table

reject the H0, the standard deviations are significantly different

what do you do if F calc is less than F table

accept the H0, the precision between the two sets isnt significantly different

what does k signify in calibration calculations

the number of replicate measurements of the unknown

what does mu +- 1 theta cover?

68.3% of expected values

what does mu+-2theta cover?

95.4% of expected values

what does mu+-3theta cover?

99.7% of expected values

what does null hypothesis mean

that there is no significant difference

what does alternative hypothesis state

that the significant difference exist

what do two tailed tests test

if a value is significantly different than a reference

what do one tailed tests test

used only when one direction matter

what do you do for external calibrations

• prep standards independently

• use 6 standard concentrations

• measure replies of unknown samples

• always interpolate within the calibrated linear range

what are the factors that minimize uncertainty

• increasing replicate measurements of the unknown (k)

• increasing the number of calibration standards (n)

• having a steeper slope

• minimizing scatter around the line

• centering y unk near the centroid mean of standards

what is linear range

signal is directly proportional to concentrations

• for quantitative analysis

what is dynamic range

range over which any measurable detector response occurs

what happens when Q < K

the chemical equilibrium moves forward ( toward the products)

what happens when Q > K

the equilibrium shifts backwards, towards reactants

what happens when Q=K

the equilibrium is established

how do you calculate formal concentrations after dilution

M1V1=M2V2

what happens when Qsp > Ksp

precipitate forms

what happens when Qsp < Ksp

no precipitate forms

how do you perform gravimetric caculations?

Mass of analyte = mass of precipitate X (FW analyte / FW precipitate) x (moles of analyte / moles precipitate)

what is Kw equal to?

1×10^-14 at 25 degrees C

how do you find pH?

-log [H3O+]

how do you find pOH

-log [ OH-]

pH + pOH =

pKw or 14.00

what is the Le Chatelier’s principle

when a system at equilibrium is disturbed, it adjusts to counteract the disturbance

when adding or removing reactant, what happens to the equlibrium

it shifts towards products

what happens when you decrease or increase pressure

pressure shifts toward fewer gas molecules

what does increased temperature favors?

endothermic reaction

what does decreased temperature favors?

exothermic reaction

what does arrhenius acid produce

H+

what does arrhenius base produce

OH-

what is bronsted lowry acid

a proton donor ( H+)

what is bronsted lowry base

a proton acceptor

what is lewis acid

an electron pair acceptor

what is a lewis base

an electron pair donor

what are ionizable hydrogens

are attached to highly electronegative atoms

• hydrogens bonded to carbon are non-polar and non-ionizable

central metal cation

lewis acid

ligand

lewis base

monoprotic

1 hydrogen

diprotic

2 hydrogens

triprotic

3 hydrogens

polyprotic

more than 2 hydrogens

monodentate

1 donor atom

bidentate

2 donor atoms

multidentate or chelating

more than 2 donor atoms

titrant

known standard solution delivered from a buret

analyte ( titrand)

solution of unknown concentration in the receiving flask

equivalence point

theoretical stoichiometric point where moles of titrant added exactly equal analyte moles

end point

physical change observed experimentally

titration error

difference between the observed endpoint volume and the theoretical equivalence point volume

primary standard

highly pure, stable, non-hygroscopic compound used to standardize titrants

what is the first derivative

endpoint is the peak maximum

what is second derivative

endpoint is the zero crossing

selective precipitation

adding a precipitating counter-ion allows separation of two cations if their Ksp values differ by several orders of magnitude

• the least soluble precipitates first

coprecipitation

an otherwise soluble compound precipitates along with the target precipitate via surface absorption or crystal lattice inclusion

• common when precipitates share identical crystal structures

when is pH = 7 at equivalence point

strong acid + strong base