We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF or read online on Scribd
You are on page 1/ 4
; CALISRA TION .
PROSLEMS
Practice Problems to Answer SAMPLE PROBLEM #1
A 5.00-mL sample of blood was treated with trichloroacetic acid
to precipitate proteins. After centrifugation, the resulting solution
was brought to pH 3 and extracted with two 5-mL portions of
methyl isobutyl ketone containing the lead-complexing agent
APCD. The extract was aspirated directly into an air/acetylene
flame and yielded an absorbance of 0.502 at 283.3 nm. Five-
milliliter aliquot of standard solution containing 0.600 ppm of lead
were treated in the same way and yielded absorbance of 0.599.
Find the concentration of lead in the sample in ppm assuming the
Beer's Law is followed ca
(mL)
0
1.00
3.00
5.00
standard
SAMPLE PROB!
20-21. (1 Standard addition. To measure Ca in breakfast cereal,
0.521 6 g of crushed Cheerios was ashed in a crucible at 600°C in
air for 2 h.*? The residue was dissolved in 6 M HCI, quantitatively
transferred to a volumetric flask, and diluted to 100.0 mL. Then
5.00-mL aliquots were transferred to 50-mL volumetric flasks. Each
was treated with standard Ca** (containing 20.0 pg/mL), diluted to
volume with HjO, and analyzed by flame atomic absorption.
Construct a standard addition graph and use the method of least
squares to find the x-intercept and its uncertainty, Find wt% Ca in
Cheerios and its uncertainty.
Absorbance
0.151
0.185
0.247
300
Ca?* standard
(mL) Absorbance
8.00 0.388
10.00 0.445
15.00 0.572
20.00 0.723
EM #2 SAMPLE PROSLEM #3
Hobbins reported the following calibration data for the flame
atomic absorption analysis for phosphorus.**
ppmP Absorbance
2130 0.048
4260 0.110
6400 0.173
8530 0.230
To determine the purity of a sample of Na,HPOy, a 2.469-g
sample is dissolved and diluted to volume in a 100-mI.
volumetric flask. Analysis of the resulting solution gives an
absorbance of 0.135. What is the purity of the NayHPO,?
