Roberts, Edwin

Roberts, L. B.

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Journal of the Arkansas Academy of ScienceVolume 1 Article 261941Modification of the Qualitative Procedure for LeadL. B. RobertsUniversity of Arkansas at MonticelloEdwin RobertsUniversity of Arkansas at MonticelloFollow this and additional works at: http://scholarworks.uark.edu/jaasPart of the Analytical Chemistry CommonsThis article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able toread, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking priorpermission from the publisher or the author.This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academyof Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu, ccmiddle@uark.edu.Recommended CitationRoberts, L. B. and Roberts, Edwin (1941) "Modification of the Qualitative Procedure for Lead," Journal of the Arkansas Academy ofScience: Vol. 1 , Article 26.Available at: http://scholarworks.uark.edu/jaas/vol1/iss1/2677MODIFICATION OF THE QUALITATIVE PROCEDURE FOR LEAD XL. B. Roberts and Edwin Roberts, Arkansas Agriculturaland Mechanical College, MonticelloThe classes in general chemistry at Monticello A. and M.College are given, toward the end of the year, a brief coursein elementary qualitative analysis for the purpose of impressingthe student more strongly with some of the characteristics of themore common metals about which he has studied, and also to aidhim in acquiring a more polished laboratory technique. In thescheme of analysis which he follows, however, we have, for thepurpose of simplification, omitted from group two the entire tinsub-group; therefore, the metals arsenic, anitmony, and tin areplaced in no unknown that he will run.Because of the lack of sufficient ventilation In the generalchemistry laboratory, we found it highly desirable to devise amethod by which we could eliminate that part of the procedure inthe second group in which the solution is boiled down to fumeswith concentrated sulphuric acid in order to separate lead frombismuth, copper, and cadmium. That could be done if lead wereprecipitated completely in the first group, thus removing thenecessity of dealing with it In the second.As lead precipitates more completely in a colder solution,experiments on the precipitation of lead from a solution cooledto a temperature of about 4°C. by means of the ice bath werecarried out by adding hydrochloric acid to the chilled solutiondropwise and with stirring, and a much more complete precipita-tion was obtained than was possible under ordinary conditions.The precipitation was not yet sufficiently complete to preventsome lead sulphide from being precipitated in the second group,but that was found to give no trouble.Since both lead and bismuth, when present in the secondgroup, are precipitated by ammonia and since small quantitiesof lead do not interfere with the sodium stannite test forbismuth, if lead is found in the first group the evaporation withsulphuric acid in the second group may be omitted without furtheralteration of procedure. However,, although the precipitation oflead in chilled solution by means of hydrochloric acid is suffi-ciently complete for most purposes, yet Iflead were present inonly very small quantities or if ammonium or acetate ions were inthe original solution, the lead might escape detection. ThereforeIt is desirable to have a method of separating lead from bismuthIn the second group.Itwas found possible to separate the- precipitated lead andbismuth by treating the hydroxides on the filter paper with 5 Nacetic acid. Such treatment of bismuth hydroxide alone, did notdissolve enough bismuth to be precipitated by hydrogen sulphide,nor did this treatment prevent the precipitate from givingpositive results with the sodium stannite test. Also, sincepotassium dichromate gives no precipitate with bismuth In acidsolutions, whatever bismuth might come through with acetic acidwould not interfere with the lead test.To test the new procedure a solution containing lead, bismuth,copper, and cadmium was prepared. This solution was chilled andhydrochloric acid was added to remove the lead. After filtration,the solution was made alkaline with ammonia and was carried throughthe revised procedure from that point on. This procedure gaveentirely satisfactory results at every step.Presented at the 1939 meeting.77Journal of the Arkansas Academy of Science, Vol. 1 [1941], Art. 26Published by Arkansas Academy of Science, 194178 umThe following scheme of analysis for group one and the coppersub-group of group two embodies the changes in procedure for lead.Take 10 cc. of the original solution, chill in an ice bath, andadd 5 N HC1 dropwlse with stirring until precipitation is complete.Filter and test the precipitate in the regular manner for the firstgroup metals.Neutralize the filtrate and add 5 cc. 3 N HC1, dilute to 50cc. so that 0.3 N HC1 solution is obtained. Treat with H2 S. Thentransfer the copper group residue to a beaker containing 15 cc. of5 N HN0 3, and an equal volume of water. Boil for two minutes,filter, and test the residue for mercury.Make the filtrate alkaline with 5 N NH3 and filter. If thefiltrate turns deep blue, the presence of copper is indicated andthe blue color must be destroyed with potassium cyanide. Testfor cadmium with H2S.Wash the precipitate from the ammonia treatment with water anddiscard the washings. If lead has been found in the first grouptest the residue with sodium stannite, a black coloration confirm-ing the presence of bismuth. Iflead has not been found and tracesmust be sought, or ifammonium and acetate ions are not known to beabsent, wash with 5 cc. 5 N acetic acid repeatedly, add 5 cc. ofwater to the washings and test with potassium dichromate. Thentest the residue for bismuth with sodium stannite solution.«fiMror mmv78Journal of the Arkansas Academy of Science, Vol. 1 [1941], Art. 26http://scholarworks.uark.edu/jaas/vol1/iss1/26

Modification of the Qualitative Procedure for Lead

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Journal of the Arkansas Academy of Science Volume 1 Article 26 1941 Modification of the Qualitative Procedure for Lead L. B. Roberts University of Arkansas at Monticello Edwin Roberts University of Arkansas at Monticello Follow this and additional works at: https://scholarworks.uark.edu/jaas  Part of the Analytical Chemistry Commons Recommended Citation Roberts, L. B. and Roberts, Edwin (1941) "Modification of the Qualitative Procedure for Lead," Journal of the Arkansas Academy of Science: Vol. 1, Article 26. Available at: https://scholarworks.uark.edu/jaas/vol1/iss1/26 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu, uarepos@uark.edu. 77MODIFICATION OF THE QUALITATIVE PROCEDURE FOR LEAD XL. B. Roberts and Edwin Roberts, Arkansas Agriculturaland Mechanical College, MonticelloThe classes in general chemistry at Monticello A. and M.College are given, toward the end of the year, a brief coursein elementary qualitative analysis for the purpose of impressingthe student more strongly with some of the characteristics of themore common metals about which he has studied, and also to aidhim in acquiring a more polished laboratory technique. In thescheme of analysis which he follows, however, we have, for thepurpose of simplification, omitted from group two the entire tinsub-group; therefore, the metals arsenic, anitmony, and tin areplaced in no unknown that he will run.Because of the lack of sufficient ventilation In the generalchemistry laboratory, we found it highly desirable to devise amethod by which we could eliminate that part of the procedure inthe second group in which the solution is boiled down to fumeswith concentrated sulphuric acid in order to separate lead frombismuth, copper, and cadmium. That could be done if lead wereprecipitated completely in the first group, thus removing thenecessity of dealing with it In the second.As lead precipitates more completely in a colder solution,experiments on the precipitation of lead from a solution cooledto a temperature of about 4°C. by means of the ice bath werecarried out by adding hydrochloric acid to the chilled solutiondropwise and with stirring, and a much more complete precipita-tion was obtained than was possible under ordinary conditions.The precipitation was not yet sufficiently complete to preventsome lead sulphide from being precipitated in the second group,but that was found to give no trouble.Since both lead and bismuth, when present in the secondgroup, are precipitated by ammonia and since small quantitiesof lead do not interfere with the sodium stannite test forbismuth, if lead is found in the first group the evaporation withsulphuric acid in the second group may be omitted without furtheralteration of procedure. However,, although the precipitation oflead in chilled solution by means of hydrochloric acid is suffi-ciently complete for most purposes, yet Iflead were present inonly very small quantities or if ammonium or acetate ions were inthe original solution, the lead might escape detection. ThereforeIt is desirable to have a method of separating lead from bismuthIn the second group.Itwas found possible to separate the- precipitated lead andbismuth by treating the hydroxides on the filter paper with 5 Nacetic acid. Such treatment of bismuth hydroxide alone, did notdissolve enough bismuth to be precipitated by hydrogen sulphide,nor did this treatment prevent the precipitate from givingpositive results with the sodium stannite test. Also, sincepotassium dichromate gives no precipitate with bismuth In acidsolutions, whatever bismuth might come through with acetic acidwould not interfere with the lead test.To test the new procedure a solution containing lead, bismuth,copper, and cadmium was prepared. This solution was chilled andhydrochloric acid was added to remove the lead. After filtration,the solution was made alkaline with ammonia and was carried throughthe revised procedure from that point on. This procedure gaveentirely satisfactory results at every step.Presented at the 1939 meeting.78 umThe following scheme of analysis for group one and the coppersub-group of group two embodies the changes in procedure for lead.Take 10 cc. of the original solution, chill in an ice bath, andadd 5 N HC1 dropwlse with stirring until precipitation is complete.Filter and test the precipitate in the regular manner for the firstgroup metals.Neutralize the filtrate and add 5 cc. 3 N HC1, dilute to 50cc. so that 0.3 N HC1 solution is obtained. Treat with H2 S. Thentransfer the copper group residue to a beaker containing 15 cc. of5 N HN0 3, and an equal volume of water. Boil for two minutes,filter, and test the residue for mercury.Make the filtrate alkaline with 5 N NH3 and filter. If thefiltrate turns deep blue, the presence of copper is indicated andthe blue color must be destroyed with potassium cyanide. Testfor cadmium with H2S.Wash the precipitate from the ammonia treatment with water anddiscard the washings. If lead has been found in the first grouptest the residue with sodium stannite, a black coloration confirm-ing the presence of bismuth. Iflead has not been found and tracesmust be sought, or ifammonium and acetate ions are not known to beabsent, wash with 5 cc. 5 N acetic acid repeatedly, add 5 cc. ofwater to the washings and test with potassium dichromate. Thentest the residue for bismuth with sodium stannite solution.«fiMror mmv

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Modification of the Qualitative Procedure for Lead

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