ANALYTICAL CHEMISTRY FINAL- ACS EXAM QUESTIONS AND ANSWERS A+ GRADED. BUY Quality Materials!
Using the same thermometer, a lab group measures the room temperature three times over the course of their experiment and they got 23.1, 22.7, and 23.3. What type of error is this: systematic, random, ...
Using the same thermometer, a lab group measures the room temperature three
times over the course of their experiment and they got 23.1, 22.7, and 23.3. What
type of error is this: systematic, random, both, or a mistake?
random error because fluctuation is + and -
You plot a calibration curve using the concentration values listed in your lab
procedure, instead of using the actual concentrations of your diluted standards
recalculated using the dilution equation. What type of error is this: systematic,
random, both, or a mistake?
mistake
During a colorimetric titration, you repeatedly read your final volume of titrant at
the point where it turns very dark blue color, instead of at the first time there is a
persistent faint blue color. What type of error is this: systematic, random, both, or
a mistake?
systematic error to be corrected, or a mistake if you can't collect meaningful data.
you transfer 5.00 mL of sample into the same volumetric flask on three separate
occasions, and record the mass. You clean out the flask with DI water and shake
it, but you do not dry the flask, after each measurement. The mass measurements
for the three trials were 47.385 g, 47.295, and 48.293 g. What type of error is this:
systematic, random, both, or a mistake?
systematic, because you can account for it and fix it.
Do method blanks, blind samples, calibration curves, spiked recoveries, and
automatic sample injection go with accuracy or precision?
accuracy. they help us get results that are closer to the true value.
Do replicated samples, and relative standard deviation go with accuracy or
precision?
Precision. They help to give us measurements that are closer together numerically.
True or false?The true value of a measurement is never known exactly.
I mean, true
True or false? The use of a student's TTEST at 95% confidence level tests one's
method for precision.
false. TTEST is for accuracy.
True or false? The mean, x, approaches the true mean, u, for small sample sizes.
false. b/c the law of large numbers
True or false? The Grubbs test (G-TEST) is used to determine if a questionable
value can be rejected as an outlier.
true
As an analytical chemist working for Coca-Cola, your supervisor has tasked you
with determining the concentration of caffeine in various samples of soda. As
part of your method, you need to prepare 500 (plus or minus 5) mL of 0.035 M (+_
0/003) M caffeine (MW = 194.19 g/mol) stock solution.
, a. calculate the mass (in grams) of caffeine that you should weigh out to make
your stock solution.
b. what is the concentration fo your stock solution in units of ppm? you can
assume the density is the same as water (1.0 g/mL)
c. Calculate both the absolute and percent relative uncertainty associated with
your mass calculation in part A, via propagation of error.
a. 0.035 mol x (194.19 g/1 mol) = 6.796 g caffeine
b. ppm is mass solute/ mass sample * 10^6. or mg/L
6.796 g x (1000 mg/1 g)=6796.65 mg/0.500L is 13593.3 ppm.
c.
relative uncertainty:
mass % = 0.003/0.0035 x 100 = 8.57145
volume 5/500 x 100 = 1%
total relative uncertainty
% rel un= sqrt (8.57`4)^2 + (1.0)^2
= total relative un = 8.629
absolute uncertainty = 8.629 /100 x 6.796
0.5864 abs un
mass +- abs un = 6.8 (+-0.6)
mass +_ rel un = 6.8 (+_9%)
Iron is typically found as an oxide in ore samples. You analyze 1.1324 g sample of
iron ore containing Fe3O4. All of the sample is dissolved in concentrated HCl.
The resulting solution is diluted with water, producing the iron (III) ion in solution.
The Fe 3+ ion is precipitated as Fe2O3 x H2O by addition of NH3. After filtration
and washing, the residue is ignited at a high temperature to drive off the water
and to give 0.5394 g of pure Fe2O3 (MW= 159.69 g/mol).
a. balance the reaction below.
_____Fe3O4 + ____O2 > _______Fe2O3
b. Calculate the mass % of Fe3O4 (MW= 231.54 g/mol). in the original ore sample.
c. your supervisor only wants ore samples with a mass % of iron greater or equal
to 45.0%. Does your sample meet this requirement?
a. 4Fe3O4 + 1O2 > 6Fe2O3
b. 0.5394 g Fe2O3 x (1 mol Fe2O3/159.69 g) x (4 mol Fe3O4/6 mol Fe2O3) x (231.54
g/ 1 mol Fe3O4) = 0.512 g Fe3O4
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