{"id":1257,"date":"2019-12-06T08:58:38","date_gmt":"2019-12-06T08:58:38","guid":{"rendered":"http:\/\/chemdictionary.org\/?p=1257"},"modified":"2019-12-06T08:58:45","modified_gmt":"2019-12-06T08:58:45","slug":"titration-indicator","status":"publish","type":"post","link":"https:\/\/chemdictionary.org\/titration-indicator\/","title":{"rendered":"Titration Indicator"},"content":{"rendered":"\n<h2>Titration <\/h2>\n\n\n\n<p>It\nis also known as titrimetry and volumetric analysis [1]. Titration is\nquantitative chemical analysis used in laboratories to find out the\nconcentration of an identified analyte (a substance to be analyzed). A reagent\nwhich is termed as titrant or titrator is prepared on the basis known\nconcentration and volume as a standard solution. The titrant react with\nanalyte, the volume used is termed as titration volume. During the titration of\nstrong acid with strong base the pH changes from 3 to 11, phenolphthalein\nindicator range from pH 8 to 10 that\u2019s why mostly used for this type of\ntitration.<\/p>\n\n\n\n<h2>Indicator <\/h2>\n\n\n\n<p>A\nsubstance that changes color of the solution in response to a chemical change.\nPhenolphthalein indicator used in acid-base titration.&nbsp; A drop of indicator is added in the start of\nthe titration, the endpoint has been appeared when color of the solution is\nchanges. Redox indicators are also used which undergo change in color at\nspecific electrode potential [2]. Different indicators are used but depend on\nthe strength of an acid and alkali. Universal indicators are not used for\ntitration because they give different color at different pH. Methyl orange or\nphenolphthalein are mainly used they cause change in color at neutralization\nwhich is easier to see the end point of titration. The most important property\nof an indicator is pH range which is depend upon the strength of an indicator.<\/p>\n\n\n\n<h2>Titration Procedure <\/h2>\n\n\n\n<p>This\nprocess contain a beaker which contain small amount of the analyte and very\nsmall amount of indicator like phenolphthalein placed underneath a calibrated\nburette which contain the titrant. Small amount of titrant is added in the\nsolution until the indicators changes the color, representing the endpoint of\nthe titration. Single drop or less than the drop of used make difference in\nbetween a permanent and temporary change in the indicator. The volume of\ntitrant used is measured and calculate the concentration of analyte through <\/p>\n\n\n\n<p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; C<sub>a<\/sub> = C<sub>t<\/sub>V<sub>t<\/sub>M<\/p>\n\n\n\n<p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; V<sub>a<\/sub><\/p>\n\n\n\n<p>C<sub>a<\/sub>\n= concentration of the analyte typically in molarity<\/p>\n\n\n\n<p>C<sub>t<\/sub>\n= concentration of the titrant<\/p>\n\n\n\n<p>V<sub>t<\/sub>=\nvolume of the titrant used measured in liters<\/p>\n\n\n\n<p>M=\nmole ratio of analyte and reactant from the balanced chemical equation.<\/p>\n\n\n\n<p>V<sub>a<\/sub>=\nvolume of analyte used typically in liters.<\/p>\n\n\n\n<h2>Types of Titration <\/h2>\n\n\n\n<p>There\nare many types of titration but the most common qualitative are acid-base\ntitration and redox titration.<\/p>\n\n\n\n<ul><li><strong>Acid- base Titration<\/strong><\/li><\/ul>\n\n\n\n<p>This\ntitration is used to find out the unknown concentration of an acid or base\nthrough neutralizing with an acid or base of known concentration. An\nappropriate pH indicator is used in the titration chamber which show the pH of\nthe solution. Phenolphthalein indicator is used because it reduce the error.\nWhen more accurate results are needed pH meter or a conductance meter is used.<\/p>\n\n\n\n<ul><li><strong>Redox Titration <\/strong><\/li><\/ul>\n\n\n\n<p>This\ntitration based on a reduction-oxidation reaction carried out in between an\noxidizing agent and reducing agent. An indicator or potentiometer is used to\nfind out the end point of titration, main constituent in the oxidizing agent is\npotassium dichromate. The color changes is not definite that\u2019s why sodium\ndiphenylamine is used. But some titration do not need an indicator because of\nintense color of constituent.<\/p>\n\n\n\n<ul><li><strong>Gas phase Titration <\/strong><\/li><\/ul>\n\n\n\n<p>This\ntitration is carried out in gas phase. In this method reactive substances are\nreacted with an excess of some other type of gas which is called as titrant. It\nhas many advantages over spectrophotometry like its measurement does not depend\nupon path length, not depend upon linear change in absorbance and also sample\nwhich interfere at wavelength used specially for analyte.<\/p>\n\n\n\n<ul><li><strong>Complexometric Titration <\/strong><\/li><\/ul>\n\n\n\n<p>In\nthis titration complex formation between analyte and titrant. That\u2019s why\nspecialized indicators are used which make weak complexes. For example starch\nindicator is used iodometric titration and chelating agent EDTA is used metal\nions titration in solution.<\/p>\n\n\n\n<ul><li><strong>Zeta potential Titration<\/strong><\/li><\/ul>\n\n\n\n<p>It\nis used to find out the iso-electric point when surface charge is zero, it may\nbe achieved by changing the pH or addition of surfactant.<\/p>\n\n\n\n<h2>Indicators <\/h2>\n\n\n\n<h3>As weak acid<\/h3>\n\n\n\n<ul><li><strong>Litmus <\/strong><\/li><\/ul>\n\n\n\n<p>It\nis a weak acid, a complicated molecule consist of HLit. The \u201cH\u201d called as\nproton which is given away while \u201cLit\u201d is a weak molecule [3]. The equilibrium\nwill be established when the acid dissolve in water.<\/p>\n\n\n\n<p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; HLit \u21cb H<sup>+<\/sup> <sub>(aq)<\/sub>\n+ Lit<sup>&#8211;<\/sup><sub>(aq)<\/sub><\/p>\n\n\n\n<p>Litmus\nin unionized form give red color while in ionized form it gives blue color.<\/p>\n\n\n\n<p><strong>When hydroxide ions are adding:<\/strong><\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter size-large\"><img loading=\"lazy\" width=\"368\" height=\"167\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-92.png\" alt=\"\" class=\"wp-image-1260\" srcset=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-92.png 368w, https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-92-300x136.png 300w\" sizes=\"(max-width: 368px) 100vw, 368px\" title=\"\"><\/figure><\/div>\n\n\n\n<p><strong>When hydrogen ions are added:<\/strong><\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter size-large\"><img loading=\"lazy\" width=\"368\" height=\"155\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-91.png\" alt=\"\" class=\"wp-image-1259\" srcset=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-91.png 368w, https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-91-300x126.png 300w\" sizes=\"(max-width: 368px) 100vw, 368px\" title=\"\"><\/figure><\/div>\n\n\n\n<p>When\nthe concentration of <em>HLit<\/em> and <em>Lit<sup>&#8211;<\/sup><\/em> becomes equal so at that\npoint the color appear is a mixture of two colors and called as neutral.\nBecause at that point the pH of the solution is 7. That\u2019s why litmus paper is\nused to test for acids and alkalis.<\/p>\n\n\n\n<ul><li><strong>Methyl orange<\/strong><\/li><\/ul>\n\n\n\n<p>It\nis the pH indicator commonly used in titration. In alkaline solution methyl\norange is in yellow color. When acid is added in the solution it gives red\ncolor. Methyl orange changes color at the pH of mid strength acid. <\/p>\n\n\n\n<ul><li><strong>Phenolphthalein <\/strong><\/li><\/ul>\n\n\n\n<p>It is also very common indicator, a weak acid used in titration. The weak acid has no color while its ion gives bright pink color. <\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter size-large is-resized\"><img loading=\"lazy\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-90.png\" alt=\"\" class=\"wp-image-1258\" width=\"502\" height=\"38\" srcset=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-90.png 344w, https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-90-300x23.png 300w\" sizes=\"(max-width: 502px) 100vw, 502px\" title=\"\"><\/figure><\/div>\n\n\n\n<p>Due\nto addition of extra hydrogen ions shifts the position of equilibrium to left\nside which turns the indicator colorless. But addition of hydroxide ions and\nremoval of hydrogen reverse the equation and turns the indicator into pink\ncolor. This is mostly happens at pH 9.3 but mixture of pink and colorless gives\npaler pink color that\u2019s why it is very difficult to detect this indicator very\naccurately.<\/p>\n\n\n\n<h2>The pH range of indicator<\/h2>\n\n\n\n<h3>Importance of pK<sub>ind<\/sub><\/h3>\n\n\n\n<p>Generally\nthe indicator is represent as HInd where \u201cInd\u2019\u2019 is an indicator while \u201cH\u201d ion\nis given away.<\/p>\n\n\n\n<p>Hind\n<sub>(aq)<\/sub> \u21cb\nH<sup>+<\/sup><sub>(aq)<\/sub> + Ind<sup>&#8211;<\/sup><sub>(aq)<\/sub><\/p>\n\n\n\n<p>K<sub>a<\/sub>\nis also called as K<sub>Ind<\/sub> its expression is written as <\/p>\n\n\n\n<p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; K<sub>Ind<\/sub> = [H<sup>+<\/sup>] [Ind]\/ [Hind]<\/p>\n\n\n\n<p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; K<sub>Ind<\/sub> = [H<sup>+<\/sup>] <s>[Ind]<\/s>\/ <s>[Hind]<\/s><\/p>\n\n\n\n<p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; K<sub>Ind<\/sub> = [H<sup>+<\/sup>]<\/p>\n\n\n\n<p>Rearrange\nthe equation so the hydrogen ion concentration is on left side,<\/p>\n\n\n\n<p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; [H<sup>+<\/sup>] = K<sub>Ind<\/sub><\/p>\n\n\n\n<p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; pH = pK<sub>Ind<\/sub><\/p>\n\n\n\n<p><strong>The value of indicators are as follow:<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"\"><tbody><tr><td>\n  <strong>Indicator\n  <\/strong>\n  <\/td><td>\n  <strong>pK<sub>Ind\n  <\/sub><\/strong>\n  <\/td><\/tr><tr><td>\n  Litmus \n  <\/td><td>\n  6.5\n  <\/td><\/tr><tr><td>\n  Methyl orange\n  <\/td><td>\n  3.7\n  <\/td><\/tr><tr><td>\n  Phenolphthalein \n  <\/td><td>\n  9.3\n  <\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h2>&nbsp;The pH range of indicators <\/h2>\n\n\n\n<p>The\nrange of indicator is not fix at one point of pH, they change very quickly over\na narrow range of pH. The addition of anything will change the color of\nsolution. For example: the dominant color of methyl orange in alkaline solution\nis yellow but addition of an acid will shift the pH of solution and the color\nappear to be an orange tint with the addition of more acid the red color will\nappear and there is no yellow color.<\/p>\n\n\n\n<p><strong>The exact values of the indicators are as follow:<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"\"><tbody><tr><td>\n  <strong>Indicator\n  <\/strong>\n  <\/td><td>\n  <strong>pK<sub>Ind<\/sub><\/strong>\n  <\/td><td>\n  <strong>pH\n  range<\/strong>\n  <\/td><\/tr><tr><td>\n  Litmus \n  <\/td><td>\n  6.5\n  <\/td><td>\n  5-8\n  <\/td><\/tr><tr><td>\n  Methyl orange \n  <\/td><td>\n  3.7\n  <\/td><td>\n  3.1-4.4\n  <\/td><\/tr><tr><td>\n  Phenolphthalein \n  <\/td><td>\n  9.3\n  <\/td><td>\n  8.3-10.0\n  <\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>In laboratory, litmus is used it changes color around pH 7 but methyl orange or phenolphthalein would be used in small amount.<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter size-large\"><img loading=\"lazy\" width=\"363\" height=\"261\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-93.png\" alt=\"\" class=\"wp-image-1261\" srcset=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-93.png 363w, https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-93-300x216.png 300w\" sizes=\"(max-width: 363px) 100vw, 363px\" title=\"\"><\/figure><\/div>\n\n\n\n<h2>Choosing indicator for titrations <\/h2>\n\n\n\n<p>To\nchoose an indicator it varies from titration to titration. <\/p>\n\n\n\n<h3>Strong Acid v Strong Base<\/h3>\n\n\n\n<p>The diagram shows the pH curve between strong acid to a strong base, for methyl orange and phenolphthalein.<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter size-large\"><img loading=\"lazy\" width=\"384\" height=\"248\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-94.png\" alt=\"\" class=\"wp-image-1262\" srcset=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-94.png 384w, https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-94-300x194.png 300w\" sizes=\"(max-width: 384px) 100vw, 384px\" title=\"\"><\/figure><\/div>\n\n\n\n<p>The\ngraph shows that there is no difference in color at equivalence point. But by\nusing phenolphthalein it would titrate at pH 8.3 and it is very close to the\nequivalence point, while methyl orange would titrate the solution but further\naway from the equivalence point.<\/p>\n\n\n\n<h3>Strong Acid v weak base<\/h3>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter size-large\"><img loading=\"lazy\" width=\"384\" height=\"248\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-95.png\" alt=\"\" class=\"wp-image-1263\" srcset=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-95.png 384w, https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-95-300x194.png 300w\" sizes=\"(max-width: 384px) 100vw, 384px\" title=\"\"><\/figure><\/div>\n\n\n\n<p>In\nthis graph the indicator methyl orange is used and change color of end product\nfrom yellow to orange which is very close to equivalence point but\nphenolphthalein is completely useless.<\/p>\n\n\n\n<h3>Weak Acid v strong base<\/h3>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter size-large\"><img loading=\"lazy\" width=\"384\" height=\"249\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-96.png\" alt=\"\" class=\"wp-image-1264\" srcset=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-96.png 384w, https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-96-300x195.png 300w\" sizes=\"(max-width: 384px) 100vw, 384px\" title=\"\"><\/figure><\/div>\n\n\n\n<p>In\nthis condition only phenolphthalein indicator works and give accurate color.\nWhich is very close to equivalence point.<\/p>\n\n\n\n<h3>Weak acid v weak base<\/h3>\n\n\n\n<p>In this case both acid and base are weak in nature that\u2019s why neither methyl orange nor phenolphthalein indicators works to give color.<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter size-large\"><img loading=\"lazy\" width=\"383\" height=\"248\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-97.png\" alt=\"\" class=\"wp-image-1265\" srcset=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-97.png 383w, https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/11\/image-97-300x194.png 300w\" sizes=\"(max-width: 383px) 100vw, 383px\" title=\"\"><\/figure><\/div>\n\n\n\n<h4>References <\/h4>\n\n\n\n<ol><li>Whitney, W.D.; Smith, B.E. (1911).\n&#8220;Titrimetry&#8221;.&nbsp;<em>The Century Dictionary and Cyclopedia<\/em>. The\nCentury Co. p.&nbsp;6504.<\/li><li><a href=\"https:\/\/en.wikipedia.org\/wiki\/Titration\" target=\"_blank\" rel=\"noopener\">https:\/\/en.wikipedia.org\/wiki\/Titration<\/a><\/li><li>https:\/\/www.chemguide.co.uk\/physical\/acidbaseeqia\/indicators.html<\/li><\/ol>\n","protected":false},"excerpt":{"rendered":"<p>Titration It is also known as titrimetry and volumetric analysis [1]. Titration is quantitative chemical analysis used in laboratories to find out the concentration of an identified analyte (a substance to be analyzed). A reagent which is termed as titrant or titrator is prepared on the basis known concentration and volume as a standard solution. &#8230; <a title=\"Titration Indicator\" class=\"read-more\" href=\"https:\/\/chemdictionary.org\/titration-indicator\/\" aria-label=\"More on Titration Indicator\">Read more<\/a><\/p>\n","protected":false},"author":6,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"rating_form_position":"","rating_results_position":"","mr_structured_data_type":""},"categories":[2],"tags":[],"multi-rating":{"mr_rating_results":[{"adjusted_star_result":3.33,"star_result":3.33,"total_max_option_value":5,"adjusted_score_result":3.33,"score_result":3.33,"percentage_result":66.67,"adjusted_percentage_result":66.67,"count":6,"post_id":1257}]},"_links":{"self":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/posts\/1257"}],"collection":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/comments?post=1257"}],"version-history":[{"count":5,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/posts\/1257\/revisions"}],"predecessor-version":[{"id":1323,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/posts\/1257\/revisions\/1323"}],"wp:attachment":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/media?parent=1257"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/categories?post=1257"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/tags?post=1257"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}