UF CHM2045L lab exam

Accuracy

A description of how close a measurement is to the true value of the quantity measured.

Precision

a measure of how close a series of measurements are to one another

sig figs for addition and subtraction

the result has the same number of decimal places as the measurement with the fewest decimal places

sig figs for multiplication and division

the result has the same number of sig figs as the term with the least number of sig figs

density formula

D=m/v

percent error formula

|accepted value-measured value| / accepted value x100

how to take a proper measurement

record the measured value plus one estimated digit

how to take a proper liquid measurement

read from the bottom of the miniscus

mass percent of solute

mass of solute/mass of solution x 100 ALSO mass of solute / (mass of solute + mass of solvent) x 100

independent variable is graphed on the

x-axis

dependent variable is graphed on the

y-axis

finding moles

(total grams) / (molar mass) = moles

mass percent of water

(grams of water lost) / (grams of hydrate before it was heated) x 100

reduction

gaining electrons

oxidation

loss of electrons

How does titration work?

Fill a burette with a known volume of an alkali, at a known concentration. Make sure the acid is in an aqueous solution at a known volume, and get it into a beaker with a pipette. Add an indicator to the acid (phenolphthalein), and begin to drop the alkali in from the burette, until the solution has turned permanently pink, indicating that the acid is now neutral. Record the volume of alkali added.

Titrant

A solution usually of known concentration that is used to titrate a solution of unknown concentration (added to the analyte)

Analyte

Substance being analyzed, usually of unknown concentration

equivalence point

the point at which the two solutions used in a titration are present in chemically equivalent amounts

end point of titration

when the titration ends (the point at which the indicator changes color)

Ideal Gas Law

PV=nRT (n is equal to the number of moles of the substance and R is the gas constant 0.082)

STP (standard temperature and pressure)

conditions of 0.00°C (273 K) and 1 atm pressure

calorimetry equation

q=mcdeltaT

Hess's Law

the overall enthalpy change in a reaction is equal to the sum of enthalpy changes for the individual steps in the process

q of the system =

-q surroundings

q of reaction =

-q solution

specific heat of water

4.184 J/gC

delta H of a reaction

sum of delta H products - sum of delta H reactants

Beer's Law

A=ebc

What does each letter represent in A=ebc

A is absorbance, b is path length (length of cuvette in cm), e is molar absorbtivity, c is concentration

when volume of a solution changes, its new concentration can be determined by

m1v1 = m2v2

rate =

k[A]^m[B]^n

Energy of a photon equation

E=hv where h=6.626E-34 and v=frequency

formal charge equation

valence electrons - sticks and dots