Chem 220 final section 1

dilution calculations

M1V1=M2V2

Adding 45 mL of concentrated HCl to a beaker of water

graduated cylinder

Glassware used to accurately transfer small volumes

graduated pipet

concentration

how much solute is contained in a given volume/mass

volume %

volume solute/volume of total solution x 100

rel. standard dev

% RSD= s/x x 100

back titration

- step 1- a known excess of a standardized reagent is added to an analyte step 2: the amount of leftover reagent is determined by a titration calculation: the analyte concentration is determined by subtracting the number of excess mol found in step 2 form the total mol added in step 1

what makes a reaction a good basis of a titration

- a large K (constant is very product favored) -fast rxn

types of titration reactions

-acid base titration -redox titration -complexometric titration (ex. EDTA, ligand) -precipitation titration (forming AgCl)

random error

-always present -equal frequency of being too high or low -to reduce: repeat experiemnt -uncertainty represented as the st. dev. of confidence interval, x+- ex

multiplication/division propagation of error

-change absolute uncertainty to % rel. uncertainty -ex/x x 100= % rel. uncer. -% et= sq rt (%e1^2.......) -change back to absolute uncer. -%et= 100( ex/ final total)

end point

-change you see in the lab

two types of t tests

-comaparing experimental data to a known value -comparing two averages each with their own st. dev. -must do an F test to see if they have similar levels of random error to see if you can pool the s -if the Fcalc<Ftable, then you can pool them

grubs test

-how to determine if a value is an outlier -Gcalc<Gtable- value is not an outlier

end point of a titration

-indicator color change -sudden change in an instrumental measurement (usually pH) -change you observe in the lab

measuring mohr pipet

-less accurate -straight

analytical balance

-most accurate, goes to 4 decimal places -nearly every measurement made in lab can be trced back to accurate weighing

sig figs for log(x)

-number of digits in the answer are the same as the sig figs of x in log(x) -log (9.9 x10^3)= 4.00

confidence interval

-range of value in which the "true" value probably lies

sig figs for propagation of error

-report only 1 sig fig for error -final answer is rounded to same # of decimals as the error

equivalence point

-the theoretical point when exactly all the analyte has been consumed by titrant

equivalence point

-theoretical point when exactly all the analyte has been consumed by titrant

volumetric flask

-to contain -at 20 degrees, temp matters

buret

-to deliver -read going down -thickness of a line is about .02 mL

transfer/volumetric pipet

-use rubber bulb -has the bubble halfway down -drain the liquid onto the wall of the vessel -don't blow out last drop -more accurate than mohr pipet and graduated cylinder

t tests

-used to see if values agree with each other

preparing solution

-weigh correct mass of pure reasgent -dissolve in vol flask -dilute with more solvent to desied vol -invert flask

how is st dev used with average

average (+- st. dev)

Glassware best used when greater access to the contents is needed

beaker

Delivering different volumes of 0.200 M HCl solution for titration of a base.

buret

Glassware used to deliver a volume not known in advance

buret

adsorption

chemicals stick to the surface of glass -acid wash can help stop this

Glassware used to prevent splashing or evaporation

erlynmeyer

addition/ subtraction propagation of error

ex= sq rt (e1^2+ e2^2....)

titration

known quantity of reagent (titrant) is added incrementally with a buret to an unknown quantity of an analyte

weight %

mass solute/mass solution

weight %

mass solute/mass total solution x 100

ppm

mg solute/L

Transferring 50 μL of an enzyme solution to a test tube

micropipet

ppb

mirogram solute/L

% rel. tolerance

ml tolerance/ mL capacity x 100

Dispensing 6.6 mL portions of a solution to a series of test tubes

mohr pipet

molarity

mol solute/L soln

molality

mol solute/kg solvent (not solution) -not temp dependent, molarity is

molecular mass

number of grams containing avos number of moleucles

atomic mass

number of grms containing avogadros number of atoms

sig figs for 10^x

number of sig figs in 10^x should be equal to the number of digits after the decimal point in x 10^1.24= 1.7 x 10^1

the real rule of sig figs

only report one sig fig for error ( ex. 0.02) -the final result is rounded to the same number of decimals as the error

tolerance

permissable deviation from the specified value -class A has lower tolerance

K

product/reactant -want a large K

accurate

results are close to the "true" value

precision

results are reproducable

systematic error

results are reproducable (precise), but not accurate -sources: imporper tech, faculty equip, poorly prepared standards -consistently too high or too low

Glassware used to make accurate solutions.

volumetric flask

Glassware used to accurately transfer a small, single volume

volumetric pipet

Transferring 5.00 mL of solution from one container to another

volumetric pipet

when is standardization necessary

when a titrant is not available at high enough purity to act as a primary standard

When should a plastic volumetric flask be used instead of a more accurate glass flask?

when perfoming trace analysis and the analyte may adsorb to a glass surface

parallax error

when your eye isnt at the same height as the liquid