Lead Chromates Effect of Hydrogen-Ion Concentration on Color of Lead Chromate Pigments from Lead Nitrate and Lead Acetate R. C. ERNST,Speed Scientific School, Uniaersity of Louisville, Louisville, Ky., . ~ N DANDREWJ. SNYDER, Kentucky Color and Chemical Co., Louisville, Ky.
T
HE color of precipitated
filtered on a suction filter, and L E A D CE-IRO1VATES were prepared f r o m dried at 60' C. for 24 hours or lead chromates has been lead nitrates and lead acetates with sodium and until dry. shown by previous expotassium dichromates varying the hydrogenThe resulting pigments were perimenters (!+, >?,10, 12, I S ) ion concentration. The acidity was regulated rubbed in bleached linseed oil to to depend on the c o n c e n t r a with nitric and acetic acids, and potassium and determine the mass tone, tints, tion of r e a c t i n g s u b s t a n c e s , and strengths. Tints and temperature, rate of m i x i n g , sodium hydroxides. T h e potentiometric method strengths were o b s e r v e d after and manner of mashing. This of Ernst, Pragoff, and Litkenhous (3) u w used mulling, 50 mg. of color, 1 gram v a r i a t i o n in color has been with quinhydrone as the indicator electrode, zinc oxide, and 12 drops of lind e s c r i b e d (1, 5 , 6, 8 , 11) as and saturated calomel electrode as the standard seed oil, 2 X 50 strokes (3). being due to t h e p r e s e n c e of half-cell. The resulting colors of the pigments of The results of these experibasic salts with normal salts, ments are given in T a b l e s I and to v a r i a t i o n in particle the two series are compared as to tint, strength, to TI. The value for the posize. and mass tone. The method is discussed as a tentiometer reading with the The effect of hydrogen-ion means of control of the color qf lead chromate c o r r e s p o n d i n g pH is given. concentration on the color of pigments. The pH of the d i c h r o m a t e lead c h r o m a t e has been insolutions comesDonding to t,he vestigated by Ernst, Pragoff, and Litkenhous ( 3 ) . Their results show that, using lead observed values of the e. m. f . are probabiy not t r u e pH acetate and potassiuni dichromate while varying the pH values. All values above a pH of 9 are doubtful ( 7 ) . of the lead acetate by means of acetic, nitric, hydrochloric, and sulfuric acids, and potassium hydroxide, the resulting TABLEI. EFFECTOF VARIATIONOF PH OF LEAD NITRATE SOLUTIONS WITH N I T R I C A C I D AKD POTASsIUM HYDROXIDE lead chromates changed from medium yellows a t a pH of (Potassium dichromate" added to lead nitrate solution) 5 to orange a t a pH of 9. Their investigation covered only LEADNITRATE LEADNITRATE chromates prepared from lead acetate and potassium dichroSAXPLE pH E. m. f . SAMPLE pH , E. m. f . M i l Z..... i U O l t 8. Millidts .~ mate. lb 4.0 -215 7 7.0 A further study of the effect of pH on the color of lead 2 2.0 -333 8 8.0 ++- 40 20 3 3.0 -275 9 9.0 80 chromates prepared from lead nitrate and lead acetate, and 4 4.0 -215 10 10.0 +140 sodium dichromate and potassium dichromate was under5 5.0 - 157 11 11.0 +200 6 6.0 - 98 taken in order t o ascertain if pH can be used to control the a Potassium dichromate, pH 2.5 (e. n&.f . , -305 millivolts), not varied. colors, and to indicate pH where the colors change from b Sample 1 is for 0.5 N lead nitrate solution. yellow t o orange. SERIESI (SAMPLES 2 TO 11). When the pH of the lead EXPERIMENTAL PROCEDURE nitrate solution is varied and potassium dichromate is used, The lead acetate and lead nitrate \$-ere prepared by re- the resulting lead chromates are medium yellows from a peated recrystallization of the pure salts from strongly acid pH of 2 to 8. At a pH of 9 a decided change occurs, the solutions. The sodium and potassium dichromates were resulting colors being orange, Sample 11 (pH 11) is the prepared by recrystallization from solutions of the C. P. reddest of the oranges, while 10 is a "brownish off-shade." The tints and strengths below 9 are those of a medium salts. The acids and bases used were of highest purity. The solutions used in these experiments were 0.5 nor- yellow, 9 is light orange, 10 is "dark and dirty," and I1 is a mal, prepared in distilled water. medium orange. The hydrogen-ion concentrations of the solutions were determined by a potentiometric method ( 3 ) , using the quin- TABLE11. EFFECTOF VARIATION O F PH OF L E 4 D NITRATE S O L U T I O S S WITH NITRICACIDAXD S O D I U X HYDROXIDE hydrone of Biilmann ( 2 ) as the indicator electrode, and (Sodium diohromate" added t o lead nitrate solution) saturated calomel electrode as the standard half-cell. LE.4D NITRATE LEADNITR.ATE The lead chromates were prepared by precipibation from Smpm pH E. m. 1. SAMPLE pH E. m. f . .Millivolts Millivolts solutions having varying hydrogen-ion concentrations. 17 7.0 - 40 -333 1% 2.0 Acids or bases were added t o the lead nitrate or acetate solu13 3.0 -275 1s 8.0 + 20 1 4 4.0 -215 19 9 . 0 + 80 tions until the desired pH was obtained. The resulting solu+140 - 157 20 10.0 15 5.0 tion was 0.5 normal and had a volume of 300 cc. To this +200 - 98 21 11.0 16 6.0 a Sodium dichromate, g H 2 . 5 (e, In. t, -305 millivolts), not varied. solution were added 300 cc. of 0.5 N sodium or potassium dichromate. Thorough agitation of the solution took place SERIESI1 (SAMPLES 12 TO 21). I n this series the pH of throughout the precipitation. The precipitates were formed in 25 * 2 seconds. The temperature xvas 25 * 0.5' C. the lead nitrate solution was varied with nitric acid and The solutions were agitated for 10 minutes after precipita- sodium hydroxide, and sodium dichromate was used. The tion. The resulting pigments were allowed t o stand until mass tones are medium yellow with a change to orange the precipitate settled, washed five times by decantation, a t a pH of 9 (sample 19). Sample 20 (pH 10) correspond221
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ing to sampje 10 is likewise off-shade, while 11 is redder than 21. The mass tones differ very little from series I. The tints and strengths are similar, but the chromates using sodium dichromate give a weaker and lighter color than those prepared from the corresponding potassium dichromates.
hydroxide. The colors are similar to other nitrates. The mass tones below a pH of 9 are a little redder than series I, and correspond more to series 111. The oranges are redder and correspond to series I. The tints are more like the acetate series below a pH of 9, but the oranges correspond to the nitrates in shade and tint. TABLE111. EFFECTOF VARIATIONOF PH OF LEADACETATE SERIESVI (SAMPLES 49 TO 58). I n this series the lead SOLUTIOS WITH ACETIC ACID AND POTASSIUM HYDROXIDE nitrate was added to the sodium dichromate. The p H of (Potassium dichromatea added to lead acetate solution) the lead nitrate was varied by means of nitric acid and sodium LEADACETATE LEADACETATE SAMPLE p H E. m. f . SAMPLE p H E. m. f. hydroxide. The series shows but little change in mass tone JMdliL‘Oh MillzDo!ts and strength for the entire series. Samples 56 to 58 are 22 6.5 - 67 27 8.0 + 20 just a trifle darker than 49 t o 55. There are no oranges 23 4.4 -239 2s 9.0 + 80 24 5.0 -157 29 10.0 +1ro in the series. Series Ti1 is redder than series 11. The tint 25 6.0 - 98 30 11.0 +ZOO 26 7.0 - 40 and strength of 57 and 58 are very good. Potassium diohromate, p H 2.5 (e. m. f., -305 millivolts), not varied.
SERIESI11 (SAMPLES 23
30). The pH of the lead acetate solutions was varied with acetic acid and potassium hydroxide. The resulting chromates (using potassium dichromate) below a pH of 9 are yellower and lighter than the corresponding nitrate yellows. Those above a pH of 9 are brownish. The mass tones of this series are similar to the nitrate yellows below a p H of 9. Samples 28, 29, and 30 are on the orange side. They are browner than the corresponding nitrates and are less desirable colors. Sample 29 is off-shade. The tints and strengths of the yellows are comparable, 28 is similar to 9, 29 is stronger than 10, but 11 is redder than 30. TO
CONCLUSION
Lead chromates prepared from lead acetate and lead nitrate with varying pH, using sodium dichromate and potassium dichromate, result in medium yellows to a pH of 9, where a decided change to orange occurs, except in series VI. There is but little difference in the mass tone, strength, and tint of the medium yellows. The precipitated wet pigments of the acetate series are lighter than the corresponding nitrate series. The mass tone and tints of the acetate yellows are redder than the nitrate yellows. Above a pH of 9 a decided change occurs to orange with the exception of series VI. The change is very sharp and definite. The oranges of the nitrate series are brighter and redder in mass TABLEIv. EFFECTO F vARI.4TION O F PH OF L E 4 D ACET.4TE tone and are more desirable pigments. SOLUTIONS WITH ACETICACIDAND SODIUM HYDROXIDE Adding the lead nitrate to the sodium dichromate gives (Sodium dichromatea added t o lead acetate solution) a redder mass tone and tint than the reverse, but the series LEADACETATE LE.4D ACETATE SAMPLE p H E. m. f . SAMPLE pH E m. f . are all medium yellows with no oranges. Varying the pH Millivolts Mllllvolls of the dichromate results in a nitrate series which is similar 31 4.4 -239 35 8.0 ++ 20 32 5.0 -157 in mass tone and strength to the acetate. 36 9.0 80 33 6.0 - 98 37 10.0 +140 The chromates, both in the case of lead acetate and lead 34 7.0 - 40 38 11.0 +ZOO Sodium dichromate, pH 2.5 (e. m. f . , -305 millivolts), not varied. nitrate using potassium dichromate, are a little stronger and darker in tint and strength than those from sodium SERIESIV (SAMPLES 31 TO 38). The chromates of this dichromate, but there is less difference below a pH of 9. series were prepared from lead acetate and sodium dichro- The acetate yellows are softer and grind into the oil more mate. The pH of the lead acetate solution was varied by easily than the nitrate yellows. The potassium and sodium means of acetic acid and sodium hydroxide. The colors are radical seems to have little effect on the hardness of the similar to series 111. The mass tones show medium yellows pigment. a little more yellow than series I and 11. Samples 37 and The pH of the lead nitrate or lead acetate solution can be 38 are lighter than 29 and 30, and also than 10 and 11. The used as a means of control of color in preparing lead chrooranges are not as good as the nitrate oranges. The tints mate pigments. and strengths are similar t o series 111. Further work is now in progress in this laboratory on the relation of pH, chemical constitution, and dispersion as reOF VARIATION OF PH OF SODIUM DICHROMATE TABLE V. EFFECT lated to the color of lead chromate pigments. SOLUTION WITH N I T R I C ACIDAND SODIUM HYDROXIDE 5
(Sodium dichromate added to lead nitrate solutionu) SODIUM DICHROMATE SODIUM DICHROMATE SAMPLE pH E. m. f. SAMPLE pH E. m . f . Millivolts
a
Mdlivolte
39 2.0 -333 44 40 3.0 -270 45 46 41 4.0 -215 42 5.0 -157 47 43 6.0 - 98 48 Lead nitrate, pH 4.0 (e. m. f., -215 millivolts),
7.0 8.0
1s
+- 40 20
;:1$ 11.0 +ZOO not varied.
TABLEVI. EFFECTOF VARIATIONOF PH IN LEADNITRATE SOLUTION WITH YITRICACID AND SODIUM HYDROXIDE (Lead nitrate added to sodium dichromate solution”) LEADNITRATE LEADNITR.ATE SAMPLE p H E. m. f. SAMPLE p H E. m. f. Mzlliuolts
0
49 2.0 -333 50 3.0 -270 51 4.0 -215 82 5.0 -157 53 6.0 - 98 Sodium dichromate, pH 2.5 (e. m. E ,
Millivolts
54 7.0 - 40 55 8.0 20 56 9.0 SO 57 10.0 +140 5s 11.0 +zoo -305 millivolts), not varied.
++
SERIESV (SAMPLES 39 TO 48). I n this series the p H of the sodium dichromate mas varied with nitric acid and sodium
LITERATCRE CITED (1) Bain, J. W., Trans. Roy. SOC.Canada, 17, Sect. III,H3-91 (1923). (2) Biilmann, Ann. chim., [ 9 ] 15, 109 (1921). (3) Ernst, Pragoff, a n d Litkenhous, IND.ENG.CHEM.,Anal. E d . , 3, 174 (1931). (4) Free, J . Phys. Chem., 13, 14 (1909). ( 5 ) Green, J . Franklin Inst., 192,637 (1921). (6) Halle, C. R., Farbe Lack, 1928,300-3. (7) Kolthoff and F u r m a n , “Potentiometric Titration,” p. 323, Wiley, 1926. (8) Kuhne, F., Farbe Lack, 1930, 230-1, 243-4. (9) Milbauer and Kohn, Chem.-Ztg.. 46, 1148 (1922). (IO) Murrel, Brit. Assocn. Advancement Sci., 1920, 110. (11) Remington, Ind. Chemist, 5, 292-4 (1929). (12) Ridley, Chem. News, 125, 12-13 (1922). (13) Zerr and Rubencamp, Handbuch der Farben-Fabrikation, 4th rev., Union Deutsche Verlagsgesellschaft, Berlin, 1930. RECEIVEDSeptember 10, 1931. Presented before the Division of Paint and Varnish Chemistry at the 82nd Meeting of the American Chemical Society, Buffalo, N. Y.,August 31 to September 4, 1931 Contribution from the Chemical Laboratories of the University of Louisville.
