Synthetic Inorganic Chemistry

78 WATER AND SOLUTION

add HC1, drop by drop, until the color changes to pink, and then
make sure that a single drop, or less, of NaOH turns the color yel-
low after thorough mixing. Record the final reading of both bur-
ettes. Calculate the number of cubic centimeters of HC1 equiva-
lent to 1 cc. of NaOH. Confirm your result by running a duplicate,
and for the final value use the average of your two determinations.
Enter your data in your note book according to the following plan:

HC1 AGAINST NaOH

First trial Second trial

HC1 end reading 41.23 cc. 41.20 cc.

Initial reading 1.33 0.05

NaOH end reading

Initial reading

39.90 cc.

40.70 cc.

0.25

41.15 cc.

42.43 cc.

0.65

40.45 cc. 41.78 cc.

1 cc. NaOH = cc. HC1 0.9864 0.9849

Average 0.9857

(d) Standardize the HC1 solution against pure anhydrous

sodium carbonate. Put some dry sodium carbonate (balance

room) into a large vial, and weigh it accurately. Transfer ap-

proximately 1 gram of the solid to a dry 300-cc. Erlenmeyer

flask. Weigh the vial again to find the exact weight of the sodium

carbonate. Add 100 cc. of distilled water to the flask, and 2 drops

of methyl orange. When the carbonate has dissolved completely,

run in the HC1 from the burette, about 2 cc. at a time, with

shaking after each addition, until the pink color disappears more

slowly on shaking; and then proceed more cautiously until a single

drop of the acid turns the color from yellow to red. If the " end

point" is overstepped, add NaOH to bring the yellow color back,

and again add HC1, a drop at a time, until the exact end point is

reached. Immediately perform a duplicate standardization with

a second sample of pure Na 2 CO 3. On the left-hand page of the

note book should be recorded the weight of the Na 2 CO 3 , and the

initial and final reading of both the HC1 and NaOH burettes.

From the total HC1 subtract the volume equivalent to the

NaOH that may have been used in titrating back. Find the

number of equivalent weights of Na 2 CO 3 equal to 1,000 cc. of

the HC1. Take the average of the duplicate determinations as