School of Medigine, Howard University
SYLLABUS
OF
EXERCISES IN QUANTITATIVE ANALYSIS
H. G. SGURLOGK
PROFESSOR OF CHEMISTRY
WASHINGTON. D. C.
BERESFORD, PRINTER, 605 F ST.
1912
GRAVIMETRIC METHODS.
I. DETERMINATION OF SPECIFIC GRAVITY.
a. A Solid Heavier Than Water.—Weigh the substance
(a) in air, (b) in water, suspending the substance from one
end of the balance by a thin wire. Subtract the weight in
water from the weight in air, divide weight in air by the
difference to find S. G. Calculate the weight of 185 c.c.
of the substance, and the volume of 250 gms. of the same.
b. A Solid Lighter Than Water.—Weigh substance in
air; weigh a sinker in water; attach sinker to the sub¬
stance and weigh both together in water. Subtract the
weight of both in water from the water-weight of the
sinker alone, add the difference to the air-weight of the
substance and divide the air-weight by this figure. The
result is the S. G. of the substance. Calculate weight and
volume as in a.
c. The S. G.- of a Liquid.—Determination of the per
cent, of alcohol in solution.
Expose the solution, water and pycnometer to the at¬
mosphere'of the room in which the experiment is to be
made till they are all of the same temperature. See that
the pycnometer is perfectly clean and dry, and weigh cor¬
rectly to the tenth of a milligram.
Fill the pycnometer with distilled water to any con¬
venient graduation on the stem, using the capillary pipette
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to take out or put in water, as necessary. Weigh cor¬
rectly ; subtract weight of pycnometer to find weight of
the water.
Again make pycnometer perfectly clean and dry, and in
the same way as for water find the weight of the alcoholic
solution, being careful to fill the pycnometer with the so¬
lution to exactly the same mark that it was filled with
water. Find the weight of the alcoholic solution ; divide
by the weight of the water to find the apparent S. G.
Calculate S. G. at 40 C. by use of factor for cubical expan¬
sion (obtain factor from instructor).
Consult Bureau of Standards' Tables for percent, of alco¬
hol corresponding to S. G. at 40 C., and report.
II. DETERMINATION OF C02.
Get apparatus (Schroetter's) and carbonate from supply
clerk. See that the apparatus is perfectly clean and dry.
Carefully weigh the bottle containing the carbonate, and
shake out on a piece of black glazed paper about two
grams of the carbonate. Again weigh the bottle and con¬
tents and subtract from first weight to find how much car¬
bonate has been taken.
Follow the directions in Olsen's Quantitative Analysis,
page 105 (office), and calculate the per cent, of C02. (Copy
the directions in Olsen and put into your note-book.)
III. DETERMINATION OF A SULPHATE.
Bring to an instructor a beaker of about 150 c.c. capacity,
labeled " Sulphate" and with your name.
Add to the solution given you about 30 c.c. of water and
a few drops of hydrochloric acid. Heat nearly to boiling
and gradually add 25 c.c. of hot barium chloride solution.
Continue the heating, nearly to boiling, for 30 minutes,
3
constantly stirring. Allow the ppt. to settle, and wash by
decantation with hot water, pouring the liquid through a
filter.
Transfer the ppt. to the filter and wash with hot water
till the filtrate no longer gives a ppt. with silver nitrate
solution. Dry the filter and contents and carefully remove
the latter without loss to a watch glass or piece of black
glazed paper. Burn the filter paper in a weighed crucible,
then add the ppt. and ignite; cool in the desiccator and
weigh. Calculate the weight of magnesium sulphate in the
solution given you.
IV. DETERMINATION OF A CHLORIDE.
Bring to an instructor a beaker as in III, labeled " Chlor¬
ide." Add about 30 c.c. of distilled water and a few drops
of nitric acid ; heat to boiling. Add slowly 25 c.c. of silver
nitrate solution, stirring meanwhile, and protect from light.
Continue the heating and stirring until the ppt. settles
readily. To the clear supernatant liquid add a drop of
silver nitrate solution to see if precipitation is complete.
Wash by decantation with hot water to which a few drops
of nitric acid have been added, pouring the liquid through
a weighed Gooch crucible. Finally wash the ppt. into the
crucible and filter off all the liquid. Dry the crucible and
contents to a constant weight at i30° C., cool in the desic¬
cator, weigh and calculate the quantity of common salt in
the solution given you.
See directions for preparation of the Gooch crucible.
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VOLUMETRIC METHODS.
V. DECI-NORMAL OXALIC ACID SOLUTION.
Get from an instructor a weighing bottle containing
pure oxalic acid crystallized with two molecules of water,
H2CA.3HA Carefully weigh the bottle and its con¬
tents, and shake out from the bottle about three grams of
the acid. Again weigh the bottle and contents and sub¬
tract from the first weight to find the amount of acid re¬
moved.
Calculate the amount of water in which the acid must
be dissolved to make a deci-normal solution (6.3 gms. ox¬
alic acid in 1,000 c.c. of water make a deci-normal solu¬
tion ; hence, 6.3 : 1,000 :: wt. of acid : x = amount of water
required).
Weighing of the acid and measuring of the water must
be done very exactly, for this solution is to be used as the
starting point in volumetric methods. The correctness of
all subsequent work will depend upon the accuracy with
which the first solution is made. Measurement of the
water should be made with volumetric flasks and burettes.
For example, if the amount of water required is 435 c.c.
a volumetric flask could be used to measyre 400 c.c., being
careful to drain it thoroughly, and the remainder added
with a burette; or, the whole amount could be measured
with a burette. If the exact amount of acid to make a
liter or half a liter is weighed the solution will be more
nearly correct if the acid is put into the flask and the flask
then filled to the mark exactly. But practically the same
results can be obtained by the first method by putting the
acid into the flask used for measuring, filling to the mark,
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dissolving and completely rinsing out with the subsequent
portions of water to be measured. If the work is done
with care the solution so made will be sufficiently accu¬
rate for the requirements.
Stopper the bottle and label " Deci-normal Oxalic Acid."
VI. DECI-NORMAL SODIUM HYDROXIDE SOLUTION.
Get from the supply clerk a piece of sodium hydroxide
for the solution. Place into a 500 c.c. volumetric flask,
add about 300 c.c. of water and dissolve. Allow to cool,
add water to the mark and shake to thoroughly mix.
With the burette, or with an accurate transfer pipette,
measure into a beaker exactly 5 c.c. of the solution, add 20
c.c. of distilled water and three drops of phenolphthalein
solution.
Fill a perfectly clean burette with N/10 oxalic acid solu¬
tion, and titrate the NaOH solution until the red color just
disappears. Repeat the test several times until the average
difference of the readings is not greater than .1 c.c.
Suppose it is found that 5 c.c. NaOH solution require 12
c.c. of the oxalic acid solution ; then, 5 : 12 : : 1 : x = 2.4 ;
i. e., as the solution now stands it is 2.4 times the strength
of the oxalic acid, and must be diluted with water to the
extent that 1 volume of the NaOH shall become 2.4 vol¬
umes, For example, 400 c.c. of the solution should be
diluted to 960 c.c. (2.4 X 400), or, 560 c.c. of water must
be added.
Such a solution will be approximately deci-normal if the
measuring is done with the care already cautioned, but it
must again be tested against the oxalic acid solution.
Proceed as before, but use 10 c.c. of the diluted solution
instead of 5 c.c.
Suppose it is found that 10 c.c. of the diluted NaOH
solution require 9.5 c.c. of the acid ; then, 10 : 9.5 : : 1 :
x = .95, or the NaOH solution is .95 N/10. The bottle
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maybe labeled "0.95 N/10 NaOH," and when used as a
test solution calculations may be made as if it were deci-
normal and then corrected by use of the factor .95. Of
course this same method would apply to a solution stronger
than N/10.
VII. DECI-NORMAL HYDROCHLORIC ACID
SOLUTION.
Measure into a 500 c.c. volumetric flask ro c.c. of con¬
centrated hydrochloric acid ; fill with water to the mark
and mix thoroughly. Proceed to standardize as in VI,
titrating with deci-norinal NaOH. Use phenolphthalein
as indicator ; but'it is to be remembered that there will be
no red color on adding the indicator to the acid solution.
The end-point of the reaction is shown by the merest pink
tinge produced permanently in the solution by the titration.
Use the same care here as elsewhere.
VIII-IX. ACIDIMETRY AND ALKALIMETRY.
Bring to an instructor two beakers marked with your
name, and on one of them " Alkali" and on the other
"Acid."
Determine the amount of alkali and of acid, respectively,
in the solutions given you, in terms of the substance re¬
quired. Titrate the alkali with HC1 solution, not oxalic
acid. Use phenolphthalein as indicator.
X. DETERMINATION OF FORMALDEHYDE.
Measure into a 250-c.c. Erlenmeyer flask 25 c.c. of deci-
normal sodium-hydroxide solution and add 25 c.c. of hy¬
drogen-peroxide solution. Weigh out about three grams
of formaldehyde solution (the exact weight must be known)
and add to the contents of the flask.
Heat on the boiling-water bath for five minutes, shaking
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occasionally. Allow to cool; titrate the excess of alkali
withdeci-normal acid (use litmus as indicator) and calculate
the per cent, strength of the formaldehyde solution.
In this experiment the formaldehyde is oxidized to formic
acid in the presence of an alkali. In working with strong
solutions of formaldehyde it is better to use normal solutions.
Exercises for which mimeographed instructions will be
provided:
Analysis of Milk : Specific gravity by lactometer; de¬
termination of total solids ; ash ; fat by Babcock's method.
Analysis of Saccharine Solution: Amount of reducing
sugar ; sucrose, Clerget's hydrolysis ; polariscopy.
Examples in analysis of Foods, Water, Drugs, etc.