Direct Titration Method for the Determination of Barium SAMUEL B. DEAL Radio Corp. o f America, Lancaster, f a .
The determination of barium by direct titration involves the titration of a barium solution with standard potassium sulfate solution, using tetrahydroxyquinone as an internal indicator. The end point of the titration is taken as the point of disappearance of the red barium salt of tetrahydroxyquinone. The method is particularly well suited for industrial control of the concentration of barium in solution.
A
approximatel> 4 before titration, using bromocresol green a.~ an indicator, and that the use of a combination of sodium chloride and silver nitrate sharpened the end point. I n 1940, Kahler (4)found that the interfering effect of sulfite could be eliminated by adding a small amount of dilute hydrochloric acid to the solution, and then boiling, cooling, and neutralizing it with sodium hydroxide solution just to the acid side of phenolphthalein before titration.
TITR.-\TIOS method for the determination of barium was needed to check the strength of barium nitrate solu-
Table 11.
tions used in the settling of phosphors of fluorescent screens. The iiiherently longer time required made a gravimetric method unsuitable for industrial control. h considerable amount of experimental work on the direct titration of sulfate with standard barium chloride has been carried out (1-12). Schroeder (6) first, proposed direct titration lor the determination of sulfate using tetrahydrosyquinone as
Barium Solution Ba(S0a)s
an internal indicator. His method involves the titration of sulfate in a sample with a standard barium chloride solution, the end point being indicated by the appearance of the red liariuni salt of tetrahydrosyquinone. Because solutions of tetrahydroxyquinone are unstable, Schroeder suggested addition of a feLv tenths of a gram of a dry dispersion of the indicator mith a large a:nount of potassium chloride to each sample on which a sulfate determination is made. Schroeder also studied the effect of acid concentration, temperature, and the presence of various other ions. The presence of hydroxyl, chloride, carbonate, silicate, calcium, magnesium, or aluminurn was found to be inconsequential, except in high concentrations. The presence of iron caused interference. sheen and &h]er ( 8 ) esteIlded the range of sulfate conrelltration, Over Lvhich the tit,ration method is applicable, They retomlnended the use of isopropyl alcohol in piace of ethyl alcohol for lowering t!ie solubility of barium sulfate and hastening precipitation. They al-o found that up to 60 p.p.ni. of phosphate ion can he tolerated if thc pH value of the sample is adjristed to -~
Table I .
~
~~~
~~~~~~~~~
BaCll
~~
Ba Solution hll. 0.0260 20.0
.v
0.025N KsSOa, hll. 20.3 20.4 20.4 20.4 20 5
Ba Ba S o h . ,
Ba e KsSOd, llg. 34.4 34.8 35.0 35.0 35.0 35.2 47,. 35,o hlg.
0.0250
20.0
20.9 20.9 20.9 21.0 20 9
34.4
02"
20,0
21.7 21.6 21.5 21.7 21.6
36.3
Av. Ba(CrHaoz)a
AV.
35.9 35.9 36.9 36.1 35.9 35.9 37.3 37.1 36.9 37.3 37 1 371
The experimental proce+ described in this paper is the reverse the titration process described in the literature mentioned; it concerns the direct titration of barium with standard potassium sulfate solution, together with a study of the interfering effect of calcium and strontium. Of
COMPARISON WITH GRAVIMETRIC IMETHOD
~-
Comparison of \'olumetric and Grav-imetric Methods" Barium Present,
Barium Found, hlg. Gravimetric Volumetric 0.5 0.7 0.9 0.7 1.0 0.8 0.9 1.0 0.8 0.7 0.9 0.7 1.0 2.5 3.9 2 2.5 2 8 3.9 2.8 4.1 3.8 2.9 2.8 4.1 4.1 2.9 35.3 35 0 3 34.3 35.0 34 8 35.3 34.9 35,l 35.0 35.5 35.1 35.0 35.1 108.1 105.9 4 105.0 105.8 108 1 105.9 107.9 105.8 107.8 105.8 108.0 106.1 107.9 0.1.v 0. Samples in groups 1, 2, and 3 were titrated with 0,025.v I
