Page 50 - Geochemistry of Oil Field Waters

38 ANALYSIS OF OILFIELD WATERS

Reagents. The necessary reagents are standard hydrochloric acid, standard
sodium hydroxide, pH buffer solutions (preferably for pH 4, 7, and lo),
mannitol, and nitrogen gas.

Equipment The necessary equipment are a pH meter, 10-ml microburets,
boron-free glassware, and boron-free reflux condensers.

Standardization of 0.02N sodium hydroxide

The 0.02N sodium hydroxide solution should be standardized to deter-
mine its exact normality. One of the better methods is to standardize it with
potassium acid phthalate. Obtain a potassium acid phthalate sample of
known purity, such as a National Bureau of Standards standard sample, and
dry the salt at 105°C. Weigh 0.1 g of salt, dissolve it in 50 ml of distilled
water, and titrate with sodium hydroxide to a pH of 7.0.

Reaction:

HOOC , ,’ COONa
‘,
NaOH + ChH, - -‘ChH,’ + H,O
/
KOOC ’ ‘COOK

Normality calculation:
weight KHCs H, 0,
= 0.20422 x ml NaOH

Standardization of 0.05N hydrochloric acid

If constant boiling-point hydrochloric acid is not used in preparing 0.05N
hydrochloric acid, the normality should be checked. One method is to use a
potassium iodate sample of known purity; for example, a National Bureau of
Standards standard sample. Dry the salt at 180’C for 2 hours, weigh 0.1 g,
dissolve it in 50 ml of distilled water, add 2 g of potassium iodide and 2 g of
sodium thiosulfate, and titrate with hydrochloric acid to a pH of 7.0.
Reaction:
KI03 + 5KI = 6HC1 + 6KC1+ 312 + 3H20
I2 + 2Na2S203 + Na2S406 + 2NaI
Normality calculation :
weight KI03
N=
0.03567 x ml HC1