CHM 145 final Flashcards
properties that do not rely on the identity of the solution but rather how much of it is present
aka the concetration
Colligative properties
expt 1.
what does the addition of a non votile solute do to the vapor pressure of a solution?
expt. 1
it lowers the vapor pressure and therefore increases the boiling point
because the surface of the solution is more cluttered so less gas
change in boiling point =
expt. 1
molal boiling point constat * molality
Kbm
moles of solute/ kg of solvent * the number of ions the solute dissociates into
molality
did salt or sugar have the higher bp and why?
expt. 1
salt (NaCl) because it dissociates into ions (aka is an electrolyte) and sugar is nonpolar (nonelectrolyte) and does not dissolve
In the experiment you had to be sure that the 150mL beaker was covered to not let the solvent escape in large quantities, what would happen if you let the solvent escape freely?
expt. 1
The molality would be affected. this would raise the boiling point of the solution past the correct point.
what were the dependent and independent variables for expt. 1 Colligative properties?
aka what did you change and what did you measure/ x and y axis
dependant variable (y): temperature change
independent variable (x): substance (NaCl or sugar)
the change in concetration of reactants or products over the change in time
depends on the reactant concentrations
reaction rate
what can catalysts change about a reaction?
expt. 2
they can lower the Ea which increases the reaction rate
proteins that lower the activation energy and are not decomposed in reactions
expt. 2
catalysts
how do you convert from the Kpa/s to M/s
expt. 2
kpa/s/(8.314*TempK)
what is the rate law from the chemical kinetics expt. 2
R=k[H2O2}^x[KI]^y
the minium energy required to bring a reaction to completion
activation energy
how do you find Ea?
ln(k)=-Ea/RT+lnA
as concentration of H2O2 decreased what happened to the reaction rate?
the reaction rate also decreased
—- in a chemical reaction occurs when concentrations are stagnant but reactions do not stop occuring
aka the rate of the forward and the reverse reactions are =
equilibrium
what is the concetration of the products and the reactants goverend by?
the equilibrium constant (Keq)
Finish the hypothesis
if the concentration of Fe3+ is held constant and the concentration of SCN is increased the absorbance of the complex ion will—
increase
What is the equation for the ionization of acid in water?
HA+H2O—A- +H3O+
A: conjugate base
If you are shown a graph of pH (Y) and log([A-]/[HA]) how do you determine pKa?
by the y-intercept of the graph
Complete the hypothesis
I expect that test tube #—will have the highest pH bc—
Test tube #12 will have the highest pH because it had the highest concentration of the base HPO42-
If pH>pKA what color will the soln be?
the color of the basic form of the indicator
if pH<pKa what color will the soln be?
the color of the acidic form of the indicator
for qualitative evaluation of the test tubes what will the pKa be?
The pKa will be = to the pH of the tube that has the most equal mixture of both the basic and the acidic form of the indicator by color
absorbance is —- to concentration
proprotional
aka =
When using derivatives to determine pKa what is the value of pKa?
the pH of the peak of the first derivative is the pKA
what is Ai in the rearranged henderson hasselbalch equation?
hint: it does not stay consistent
it is the absorbance at each measurments pH
what is Aa in the rearranged Henderson Hasselbalch equation?
hint: it stays consistent
the most acidic measurements absorbance
What is Ab in the rearranged henderson hasselbalch equation?
hint: it stays consistnet
the most basic measruments absorbance
how do Ai, Ab and Aa fit into the re-arranged henderson hasselbalch equation
pH= pKa +log (Ai-Aa/Ab-Ai)
an aq. solution of a weak acid and its conjugate basae
Buffer
What are three ways a buffer can be made?
- adding a weak base to strong acid
- adding weak acid to strong base
- adding salt of an acid to the acid
the capacity of the buffer to consume acid is limited by its concentration of —
base
A-
the capacity of the buffer to consume base is limited by its concentration of —
acid
HA
If the pKa of a buffer is 6.2 what would be a range the buffer would be effective in resisting change?
expt 5
5.2-7.2
How do you calculate the expected buffer capacity? / what do you need to calculate it?
expt. 5
concentration of the base in the buffer and the amount of moles of acid needed to ‘break ‘ the buffer and volume of the buffer
The extent to which a dissolution reaction occurs is dependent on the —- of the —-
expt 6
Magnitude, Ksp
For a precipitate to form Q must be —- than Ksp
expt 6
larger
Q>Ksp
True or false? the larger the pKsp value the harder it is to form a precipitate?
False, any pKsp value larger than 7 is easily formed and stable
What is a flame test useful for finding?
If Na is present in a solution
What is a Fe(salicyltate) test useful for finding?
expt 6
H2PO4-
What is a AgNo3 test useful for finding?
expt 6
If a halide (Br, I, Cl-) are present in a solution
What are acceptable places for collecting nitrate field samples?
expt 7
Pond, stream, river
what device was used to determine voltage of the nitrate solutions?
expt 7
ISE (ion selective electrode)
what were the x and y axis of the calibration curve used to determine nitrate concentration?
expt 7
x- axis: Log (concentration of nitrate)
y-axis: measured potential (mv)
An electrochemical devices that allows for a redox reaction to occur spontaneously while transferring electrons externally
Voltaic cell
expt 8
to be oxidized is to —
lose electrons
to be reduced is to —
gain electrons
electrons flow from the — to the —
anode, cathode
how do you know which species is the cathode based on the standard potentials?
which ever one is most positive will be the cathode value
most negative will be anode value
How do you calculate standard deviation?
- take all the sample values and subtract the mean from them then square that value
- add those squared values together and divide that by n-1
- Take the dividie value and x^.5
T-test equation for comparison to an accepted value
I u-meanI > t*Sm
t= n-1
T-test equation for comparison of two values that have the same number of measurements
Im1-m2I> t(Sm1^2 +Sm2^2)^.5
t= 2n-2
T-test equation for comparison of two values that have a different number of measruments
Imean1-mean2I>tS12((n1+n2)/’n1n2)^.5
t= n1+n2-2
If the equality holds in a T-test what does this mean?
the values are statistically significant
