CHEMISTRY 311 - ASSIGNMENT 1
Hand-in your answers in a neat organized format to the appropriate number significant figures,
showing chemical equations and calculations where appropriate.
Due date: Tuesday, September 27th
1. What mass of Na2HPO4.3H2O and KNO3 is required to make 500. mL of a combined
stock solution containing 50.0 ppm P and 100.0 ppm N? If a 5.00 mL aliquot of this
solution is transferred to a 250 mL volumetric flask and diluted to the mark with
deionized water, what is the final phosphorus and nitrogen concentration in units of ppb
and µM.
2. Municipal sewage sludge is being tested for use as an agricultural soil amendment
fertilizer and suspected of contamination by aluminum. A 5.242 g sample of the dry
sludge is treated to dissolve all the metal ions and the aluminum is precipitated by adding
an excess of 8-hydroquinoline (C9H6NOH) to yield 0.1653 g of dry solid precipitate.
Al3+ + 3 C9H6NOH  Al(C9H6NO)3(s) + 3 H+
a) What is the concentration of Al in the original sample in ppm by mass?
b) What assumptions are involved in making this gravimetric determination?
3. In an effort to establish a new method for the analysis of cadmium in blood, a standard
reference blood sample with a certified Cd concentration of 88.2 µg/kg was analyzed five
times and yielded the following results.
83.6 69.0 83.4 96.0 76.4
Report on the precision and accuracy of the method indicating how each is influenced by
determinant and indeterminant errors.
4. Alkalinity of a water sample is a measure of its acid neutralizing ability. The total
alkalinity is determined by titrating a water sample with a standardized acid to a methyl
orange endpoint (pH ~ 4.3). What volume of 0.0160 N H2SO4 titrant is required to titrate
a 100.0 mL wastewater with the following characteristics: pH = 9.30, [CO32-] = 0.54
mM, bicarbonate ion = 68 ppm as C and 200 ppb NH3? What percentage of the total
alkalinity is due to bicarbonate ion in this sample?
5. A volumetric analysis of calcium ion uses ethylenediaminetetraacetate (EDTA4-),
which forms a 1:1 complex with Ca2+ using a field portable Hach Digital Titrator.
Calculate the molar concentration of EDTA titrant for use in this method, such that each
digit increment (resulting in a 1.25 µL delivery of titrant) corresponds to 1.00 ppm
CaCO3, when titrating a 25.0 mL water sample.
CHEM 311 Assign 1 2011
6. A hydrochloric acid titrant was standardized as follows;
• accurately weigh ~0.1 g of dry primary standard grade of Na2CO3 was weighed into
a 125 mL flask and dissolved in ~25 mL of deionized water to which was added 3
drops of bromocresol green indicator
• titrate with HCl until it just turns from blue to green, at which point it is heated to a
boil to expel CO2 and the solution returns to a blue colour
• let cool and continue titration until solution turns green
• titrate a blank solution prepared from 3 drops of indictor in 50 mL of 0.05 M NaCl
and subtract the blank volume from that required to titrate the Na2CO3
2 HCl + Na2CO3  CO2 + 2 NaCl + H2O
a) What is meant by the terms standardization and primary standard?
b) Why is it important to accurately record the mass of Na2CO3 used, but not the volume
of water it is dissolved in?
c) Why is it necessary to remove CO2 before the endpoint?
d) What is the purpose of the titration blank?
e) Calculate the mean HCl molarity, standard deviation and relative standard deviation
from the data table below.
Mass of Na2CO3
Volume of HCl delivered
(±0.1 mg)
(±0.03mL)
126.0
23.77
105.4
19.51
122.8
22.85
7. The concentration of dichromate ion (Cr2O72-) in electroplating waste may be
determined by titrating with a standardized solution of ferrous ammonium sulphate (FAS).
Fe2+ + Cr2O72- + H+ ----------> Cr3+ + Fe3+ + H2O
a) Calculate the normality of dichromate if a 100.00 (±0.08) mL sample required 14.20
(±0.03) mL of 2.42 (± 0.08) x 10-3 N of FAS to reach the end point (unbalanced reaction
given above).
b) What is the concentration of dichromate - chromium in mg/L?
c) Use the reported uncertainties in each measured quantity to propagate the uncertainty
in the final result in part b above.
8. The Kjeldahl procedure was used to analyze 520 µL of a solution containing 79 mg of
protein per mL. The liberated NH3 was collected in 5.00 mL of 0.0336 M HCl, and the
remaining acid was back-titrated with 6.34 mL of 0.010 M NaOH for complete titration.
a) What is involved in the Kjeldahl procedure?
b) What is the weight percent of nitrogen in the protein?
CHEM 311 Assign 1 2011