CHEM Lab Final
A ______ standard deviation indicates high precision while a ______ standard deviation indicates a low precision.
small, large
How did we know when Zinc and Iodine had finished reacting? What was this reaction's equation?
The color of the solution turned from light yellow --> dark brown --> colorless (finished) Zn + I2 --> ZnI2
Which measurement (in PV=nRT) in the IGL experiment cause the most uncertainty?
volume it had the largest amount of uncertainty & could have easily been misread
How did we rearrange the two ∆G calculations into a linear form?
y = mx + b ln(Ksp) = (-∆H/R)(1/T) + ∆S/R
What are the two equations used to calculate ∆G in the Thermodynamics lab? Why were there two?
∆G = -RTln(Ksp) ∆G = ∆H - T∆S Free Energy can be related to K or ∆H & ∆S
What are the molecule names for Synthesis of a Compound?
Ferric Chloride: FeCl3 + Potassium Oxalate hydrate: K2C2O4 x H2O forms: potassium trioxalatoferrate(III): K3[Fe(c2O4)3] x 3H2O
What is K from the thermodynamics lab (what is excluded)?
K = [products] / [reactants] = [Na+]^2 [B4O5(OH)4^2-] ** remember: pure l & s are excluded **
Boyle's Law
P1V1=P2V2
Ideal Gas Law. How did we use this to determine the ID of an unknown metal?
PV = nRT experiment: solve for n n=PV/RT this worked because we were able to calculate the moles while keeping pressure of the gas, volume and temperature constant. Then, we used molar mass to determine the atomic weight.
What did we conclude from the pennies experiment (regarding copper and zinc)?
Pennies made with mainly Cu were heavier than pennies made with mainly Zn. Therefore, Cu is heavier than Zn.
How did we calculate the # moles I that reacted with Zinc?
"split the bonds" between the two I atoms (I2) moles I = 2 x moles I2 Then used the Law of Definite Proportions to find empirical formula
*** Show that for an accuracy of 1% in weighing a 50g sample, a balance which is uncertain to the 0.5g is required.
% uncertainty=(absolute uncertainty/measurement) x 100 % uncertainty = 1/50=0.02
dF= ??? dC
(9/5)dC + 32
In the Thermodynaimcs lab, what was the balanced eq. equation?
(Na2B4O7)(10H2O) <---> 2Na^+(aq) + B4O5(OH)4^2-(aq) + 8H2O(l)
% Error =
(|accepted-observed|/accepted) x 100
Calculate the percnt error if observed values are 121.5, 122.3, 121.9 and the accepted value is 122.1.
0.2%
Calculate the average and standard deviation for these measurements: 74.6, 75.2, 73.7.
74.4, 0.6
on p. 99 of the manual, calculate the frequency (Hz) & energy in kJ.
690 nm 4.35 x 10^-14 sec^-1 174 kJ/mol
What were the sources of error that accounted for the mol ratio (Zn:I) to be too high or too low? Why?
Iodine moles are divided by Zinc moles: I/Zn -too low: Zn moles were calculated to be too large -too high: Zn moles would have been calculated to be too small errors: -too low: lost excess Zn somehow (perhaps when drying) -too high: not weighing excess Zn accruately or not drying it enough
How did we calculate the concentration of each solution in the Abs Spec experiment?
MconcVconc = MdilVdil Mconc = concentration of stock solution (known) Vconc = volume of stock in total solution (known) Vdil = volume of water in total solution (known) Mdil = concentration of solution
What were the two balanced equations used in Hess's Law experiment?
Mg(s) + 2HCl (aq) -->MgCl2 (aq) + H2 (g) MgO(s) + 2HCl(aq) --> MgCl2(aq) + H2O(l)
How do you calculate standard deviation?
S.D. = sqrt((d1^2 + d2^2 + ...+ d#^2)/(n-1)) where n = num measurements dx^2 = (measurement-avg)^2
What measures %T & Absorbance? What are these formaulas?
Spectrometers %T = (I/Io)100 where I=light transmitted, Io=amount that initially strikes matter Absorbance=log(Io/I)=log(%T/initial amount)
How do you calculate heat evolved in Hess's Law lab?
q = mC∆T
What is the Law of Definite Proportions? What did we use this for?
The ratio of the masses of the reactants are proportional to the ratio of their atomic weights: 2Cu + S ---> Cu2S mass Cu/mass S = X(atomic weight Cu/atomic weight S) solve for X --> yields the result CuxS We used this to determine the empirical formula of Zinc Iodide
How did we calculate the pressure of the gas during the ideal gas law experiment? Why did we do this?
The reaction beween the metal and the water resulted in hydrogen. However, due to temperature change, the gas collected resulted in being both H2 & H2O. We calculated the pressure by using Dalton's Law of Partial Pressures and then subtracted the H2O pressure. We needed to subtract this value because the reaction involved H2, not H2O.
Charles' Law
V1/T1 = V2/T2
Avadagro's Law
V1/n1 = V2/n2
In the IGL experiment, how would failing to account for trapped air inside the graduated cylinder affect the calculation of: a) vol H2 b) # moles H2 c) molar mass of metal sample
a) calculating more water volume than actually present b) increase the # moles calculated, since vol increased c) cause the molar mass to decrease (g/mol), because moles woud have been larger
In the IGL experiment, why were we able to use the # moles of H2 to calculate the atomic weight of the unknown metal?
because H2 had the same mol to mol ratio in the equation (there was the same amount of each): M (s) + 2HCl (aq) --> MCl2 (aq) + H2 (aq)
How did we determine the experimental concentration of each solution in the Abs Spec experiment? Why?
by estimating from the calibration curve (concentration vs. absorbance) & the Spectrum graph (Absorbance vs. wavelength: this shows where lambda max is, which we then plot on c.c., which then shows usconcentration at lambda max) equation: exp. conc = (unknown absorbance - intercept) / slope
How do you calculate ∆Hrxn for Hess's Law lab?
by subtracting the two equations: ∆Hrxn = ∆Hrxn(A) - ∆Hrxn(B)
When synthesizing the Coordination Compound, how did we determine the limiting reactant?
calculate the # moles of each reactant, proceed all the way until the product. The result that is lower
What is frequency?
f = c / λ rate at wavelength occurs over time
Energy of Light: E = ?
hc/λ where h=planck's constant=6.626 x 10^-34 c=speed of light=3 x 10^10 λ=wavelength
**In the IGL experiment, why is it necessary to bring both sides of the apparatus to an equal volume?
it will be read as greater than it actually is???
density=
mass/volume
