The Students' Guide in Quantitative Analysis - Free Ebooks Library

ALKALIMETRV. 43
I-LjSO^ of sp. gr. 1.840 with three or four times its volume
of distilled water ; cool and dilute to one litre. The ex-
act staodard of this solution is determined by testing with
sodium carbonate, as below.
3. Sodium Carbonate Sijlution. — Weigh off about 12
grms. anhydrous C.P. Na^COj ; heat in a porcelain dish
to low redness, stirring until moisture is expelled ; place in
a desiccator to cool. Weigh out accurately 10.6 grms. of
this, and dissolve in distilled water. Dilute to exactly 200
c.c. This gives a half noirniat solution, each c.c. of which
contains 0.053 grm. of sodium carbonate, as shown by this
simple calculation
:
Na, --= 46
C =12
O. == 48
Mol. wt. of Na.COs 106
One-half the mol. wt. = 53
200 c.c. : r c.c. -= 10.6 grms. ; 0.053 grms.
This solution serves to standardize the sulphuric acid.
Standardizing- the Sulphuric Acid.—Take of the Na^COj
solution, 20, 30, or 40 c.c, accurately measured, place in a
wide-mouthed flask of about 300 c.c. capacity ; add litmus
solution, and run in H^SO^ solution from a burette until
a wine-red color is obtained ; boil hard to expel CO;,, and
add more acid until the color is permanent. Read off the
c.c. used. Repeat the process. Suppose 30 c.c. Na.CO^
solution required 25 c.c. HjSO^ solution. Then 5 c.c.
(30— 25) water must be added to every 25 c.c. of the acid
solution to make it normal. Measure, therefore, the
H,SO^ solution carefully and add the necessary amount of
water. Suppose the HjSO^ solution measures 900 c.c.,
since 900:=: 25X36, then 36 X 5, or iSo c.c. water must
be added. Add the water, mix well, and again determine