This 13 page thesis examines the organic compound nitrazine as an indicator in acid - base nitrations

Nachod, Grace

English

Ursinus College

Ursinus College Digital Commons @ Ursinus College Chemistry Honors Papers Student Research 5-1938 A Study of the Organic Dye Nitrazine as an Indicator for Acid-Base Titration Grace Nachod Follow this and additional works at: https://digitalcommons.ursinus.edu/chem_hon  Part of the Chemistry Commons Click here to let us know how access to this document benefits you. A Study of the Organic Dye Nitraeine as an Indicator f o r Acid-Base T i t r a t i o n Ursinus College L i b r a r y . URSINUSIANA COLLECTION Class 0 BoxdSk^^-i Submitted i n p a r t i a l f u l f i l l m e n t of the requirements for Honors i n Chemistry, Approved by ̂  J. ̂ ( ^ A j , ^ ^ ^ 2 : < ! ^ ^ u b i i i i t t e d by ( 1 5 ? Nitraz.ine i s an organic compound ti at i s purple i n basic solution and yellow i n acid. The determinations indicated i n the following tables and graphs v/ere made by means of a student potentiometer balanced against a standard Weston c e l l , using a saturated calomel electrode and a quinhydrone electrode. The observed electromotive force wras converted to pH hy substituting i t i n the formula: .4554- observed E.M.F. .058 The t i t r a t i o n s were carried out at approximately 25 * Centigrade, although t h i s varied somewhat. The error introduced hy a s l i g h t change i n temperature i s n e g l i -gible, so that no definite attempt was made to regulate i t . T i t r a t i o n of a Strong itcid with a Strong Base Usinq .0983 normal KaOH and.l normal H€1, one drop of solution would change the indicator to a neutral color and another drop would change i t to either purple or yellovv, depending upon which v;ay the t i t r a t i o n was being made. The neutral color i s orange with a bluish tinge. Since a drop i s approximately ,05 m i l l i l i t e r , the color w i l l show a definite change upon the addition of .1 mil. of either acid or base. The end point i s s l i g h t l y on the acid side of actual n e u t r a l i t y . T i t r a t i n g .1 normal R€l with .0983 normal NaOH, the solution changes from yellow to purple at a pH between 5.08 and 6.47, while i n the back t i t r a t i o n with l i f l , i t changes bet-'een 7.20 and 5.96. By t i t r a t i n g back and forth around the end point, the pH range was narroived down to l e s s than IpH unit. I n eleven out of thirteen byck t i t r a t i o n s , t h i s range v/as observed. Of the two remaining changes, one was approached by adding HCI to 30 mil. of NaOH, and the other by adding NaOH to 30 mi l . of nCl. Even i n these t i t r a t i o n s , however, the v i s i b l e range i s s t i l l under 1.5 pi •units. These results have been recorded i n Table 1 and Graph 1. T i t r a t i o n of a Weak Acid with a Strong Base I n t h i s t i t r a t i o n , .1941 normal NaOH was added to 30 mi l . of ,2119 normal GĤ CGOH. The indicator changed from yellow to purple v/ithin a range qf l e s s than 1 pH uni t , but due to the v/eak ionization pfN^ie acid, t h i s range covered the addition of about .5 mi l . of NaOH. I t was noted that i n th i s case the indicator tunaed rather pink instead of the usual deep purple. For further data, see Table 11 and Graph 11 T i t r a t i o n of a Weak Base v/ith a Strong Acid By adding ,2092 norraal I l 6 l to 25 mil . of .1548 normal I. NH+OH, a reasonably vrell defined end point was obtained. The pH range was under 1 unit and was covered by the not quite as sharp as i n the strong acid-strong base t i t r a t i o n , i t v/as sharper than that observed i n a weak acid-strong b; se comi)ination. The complete data f o r t h i s t i t r a t i o n has been tabulated i n Table 111 and Giaph 111. addition of .2 mi l . of r i e i . although the end point was 3 T i t r a t i o n of Carbonates For t h i s t i t r a t i o n the solutions f i r s t used were rather d i l u t e ; the H61 was .1 noimal and the NajCO, was ,05 normal. No sharp end point could be obtained. Upon the addition of approximately 13 m i l . of H61 to 25 m i l . of Na;iC03 , the solution became p r a c t i c a l l y colorless and remained so during the addition of about 3.5 mil. more. After t h i s point was reached, a yellov/ color gradually appeared. In order to determine whether t h i s absence of a sharp end point was due to d i l u t i o n or to the effect of the 00̂ ., stronger solutions were used. However, the same effect was obtained using .2 normal Na^COjand .2092 normal H6l. This seemed to j u s t i f y the conclusion that the peculiar behavior of the indicator was due to the CÔ . Nitrarine indicator i s very s a t i s f a c t o r y f o r the t i t r a t i o n of strong acids with strong bases beceiuse i t has a sharp end point and because the two colors are so d i f f e r -ent that the change i s e a s i l y perceptible. I t may be used with f a i r l y good results with weak acid-strong base or vveak base-strong acid mixtures. The l a t t e r combination, however, gives a better end point than the former. Because of the effect of the 00^ given off i n Carbonate t i t r a t i o n s , Nitrazine i s not at a l l satisfactory f o r use i n such procedures. The color change i s confined to a rather narrow pH range, but i t i s d i f f i c u l t to say exactly what t h i s range i s . By reference to the Tables i t w i l l be seen that, i n general, color changes hfve been observed from a pH of approximately 5.7 to 6.7. Table I T i t r a t i o n of 30 m i l , of .1 N H61 with .0983 N NaOH mi l , of NaOH E.M.F. ^ 0 .3373 2.00 10 .3212 2.28 15 .3170 2.35 20 .3095 2.48 25 .2972 • 2.69 26 .2962 2.71 27.1 .2937 2.75 28 .2902 2.81 29 .2787 3.01 29.5 .2625 3.29 29.8 .2572 3.38 30 . 2488 3.53 30.1 .2367 3.74 30.2 .2048 4.29 30.3 .1588-yellow 5.08 30.4 .0781-purple 6.47 30.6 .0288 7.32 30.7 .0086 7.67 30.8 .0000 7.82 31.1 .0230 8.21 31.5 . 0425 8.55 32. .0577 8.81 • ^ Table I (cont'd) Back t i t r a t i o n with .1 N H61 mi l . of Hcl E.M.F. 0 -.0577 8,81 .1 -.0505 8.69 -.0418 ,4" * 8.54 -.0365 8.45 •• . .4 • • ' • -.0329 8.38 .5 -.0261 > 6.27 .65 -.0214 8.19 -.0190 8.14 .8 - -.0216 8.03 .9 -.0094 7.98 1.0 -.0024 7.86 1.1 -.0029 7.77 1.2 -.0087 7.67 1.3 -.0207 7.46 1.4 - . -.0357 7.20 1.5 -.0844-puiple 6.36 1.6 -.1076-yellow 5,96 Bac k t i t r a t i o n with .0983 N NaOH mi l . of NaOH E.M.F. .13 .0762-puiple 6.50 .2 .0528 6.91 .0356 7.20 .4 .0237 7.41 .5 .0137 7.58 .6 .0033 7.76 -.0122 8.03 1.0 -.0162 8.09 1.65 -.0337 8.39 Table I (cont'd) Backtitration v/lth .1 N Hdl mil , of H61 E.M.F. ^ .5 -.0262 8.61 .7 -.0208 8.17 .9 -.0131 8.04 1,0 -.0065 7.93 Backt i t r a t i o n with .0983 N NaOH mi l , of NaOH E.M.F. ^ .05 .1010 - neutral 6.08 .1 .0887 - purple 6.29 Backtit r a t i o n with H N H61 mi l , of H61 E.M.F. M .05 • .0961 6.16 .1 .1017-neutral 6.06 .15 .1055-yellow 5.99 r Table I I T i t r a t i o n of 25 m i l , of .2119 K CM,COOH with .1941 N NaOH ,of NaOH l.M.F. 0 .2965 2.71 5 .2671 3.21 10 .2426 3.63 18 .2354 3.76 15 .2122 4.16 18 .2094 4.21 I f .2020 4.33 80 .1956 4.44 21.05 .1778 4.75 21.5 .1730 4.83 88 .1699 . 4.89 83 .1635 5.00 84 .1575 5.10 85 .1525 5.19 25.55 .1467 5,29 25.7 . 1435 5.34 25.8 .1397 5.41 26.2 .1315-yellow 5.55 26.3 .1255 5.65 26.4 .1127 5.67 26.5 .1080 5.96 26.6 .0909-purple 6,27 26.85 .0132 7.59 27 .0263 7.36 I Table I I I T i t r a t i o n of 25 m i l , of .1548 N MH OH with .2092 N H61 of EGl E.M.F. 0 -.0962 9.48 5 -.0311 8.35 7.5 -.0213 8.18 9 -.0146 8.07 10 -.0106 8.00 11 -.0063 7.93 11.4 -.0024 7.86 11.6 .0000 7.82 IE .0028 7.77 12.5 .0046 • ̂  7.74 13 .0080 7.68 14 .0116 7.62 15 .0178 7.51 16 .0246 7.39 17 .0264 7.36 18 . 0385 7.15 18.5 .0488 6.98 19 .0663 6.67 19.1 .0712 6.59 19.2 .0775-purple 6.48 19.3 .0855 6.34 19.4 .1092-yellow 5.93 19.5 .1627 5.01 19.6 .1772 4.76 19.7 .1857 4.62 20 .1950 4.46 Table I I I (cont'd) m i l , of H61 E.M.F. ^ 21 .2113 4.17 22 .2351 5.76 23 .2393 3.69 24 .2450 3.59 25 .2533 3.45 /o /s" M i l . NaOrt XT T i t r a t i -l ow lY iV,i6H Sizmnary of Experiments Carried Out 1. T i t r a t i o n of a strong acid v/ith a strong base. 2. T i t r a t i o n of a ?/eak acid with a strong base. 3. T i t r a t i o n of a weak base with a strong acid. 4. T i t r a t i o n of Carbonates. 5. Standardization of solutions used. Bibliography Findlay, .ilexander - P r a c t i c a l Physical Chemistry Longmans, 1935 Chapter X I I 

A Study of the Organic Dye Nitrazine as an Indicator for Acid-Base Titration

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A Study of the Organic Dye Nitrazine as an Indicator for Acid-Base Titration

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