672
JOURNAL OF CHEMICAL EDUCATION
.
MARCH, 1930
"CHLOROX" PROBLEM FOR CHEMISTRY STUDENTS The problem outlined in this communication was recently assigned to my chemistry students. Although i t proved a humdinger for most of them a t this stage of their meager knowledge of chemistry, they evinced a real interest in it. This problem is based on the actual experiment on chlorine performed by the students the previous week. They emptied the contents of their generators and their various bottles into suitable receptacles, and from this material the "Chlorox" was manufactured. This experiment was carried on where members of the class could inspect it a t any time. The final product was given to the janitors, who made good use of it. No account was taken of the manganous chloride that could be obtained as a by-product. Another problem for future use. The problem is stated as follows: A chemistry class of 60 prepares chlor@e, each using 20 grams of MnOz and 125 The hydrochloric acid has a specific gravity of 1.18 and a concentration of36%. Each student collects three 250-cc. bottles of CI2, and saturates 100 ec. of water with i t (3 voldmes of Cb t o 1volume of water), and loses about 450 cc. of the gas. Following this the student saturstes 125 cc. of a 10% NaOH solution (sp. gr. 1.11) with CL, thereby preparing "Chlorox." The MnO* costs $0.25 per pound, the hydrochloric acid 80.20per pound, and the NaOH (solid) $0.15 per pound. (453 g. per pound.) The equations far the above reactions are: cc. of hydrochloricacidforitspreparation.
+ +
MnOz 4HC1 = MnCh CI2 = NaClO 2NaOH
+ 2HnO + CL + NaCl + H 2 0
,
(1) (2)
The following calculations are then assigned: (a)
(b) (c)
(d) (e)
(f) (g)
(14
(i)
The amount of MnOz used by the class. The grams of hydrochloric acid used by the class. The grams of HCI present in this amount of acid. The grams of HC1 actually required for the above reaction. How much excess hydrogen chloride was used? How many liters, and how many grams of Cb would be generated, using the MnOz as the basis of calculation? Haw much CI. did the class usc up to thc point of thc preparation of the "Chlorox"? How much Cl? was left with which t o saturate the NaOH solution? How many grams of NaOH (solid) did the class use?
VOL.7, NO. 3
CORRESPONDENCE
673
(1
H o w much Clr would he required to saturate this much NaOH? How much additional MnO* will have to be supplied t o generate suEcient CL t o completely saturate the NaOH? (1) Will any additional HCI have t o be supplied? Why? (m) HOWmany grams of sodium hypochlorite (NaCIO) will be made? (n) What is the total cost of this problem? What cost should be charged t o the preparation of the NaClO? (o) (p) A t a concentration of 50 g. t o a quart of water, how many quarts of "Chlorox" could he made? ( 9 ) At $026 per quart what would this amount of "Chlorax" cost t o buy? Compare the c o t of "Chlorax? computed in ( 9 ) with the cost of production hy (r) thc class as found in ( 0 ) .
(k)
VERNONC. SHIPPEE ORANGEUNION HIGHSCHOOL ORANGE. CALIFORNIA
