{"id":160,"date":"2012-09-06T12:59:45","date_gmt":"2012-09-06T16:59:45","guid":{"rendered":"http:\/\/web.colby.edu\/ch331public\/?page_id=160"},"modified":"2016-09-12T21:44:47","modified_gmt":"2016-09-13T01:44:47","slug":"ph-measurements","status":"publish","type":"page","link":"https:\/\/web.colby.edu\/ch331public\/ph-measurements\/","title":{"rendered":"pH measurements"},"content":{"rendered":"
\n

The goal of this lab is give you experience reading technical manuals for standard chemical analysis, interpret these manuals in the context of your particular analytical application, and communicate your analytical results in a complete and succinct report.<\/p>\n

Background:<\/strong> \u00a0We will discuss the specifics of pH measurements in great detail in the final third of the semester. \u00a0For now, pH measurements will be made using an electrochemical cell with both the sensing (pH) and reference electrode built into a single combination electrode. \u00a0 The potential of the combination cell in millivolts is directly related to the pH of the solution.<\/p>\n

electrode potential (E) = E’ – slope (pH) \u00a0(1)<\/p>\n

where E’ is a reference potential and the slope is the Nernst slope (theoretically 59.16 mv\/pH at 25 0<\/sup>C). \u00a0Notice that equation 1 is a simple linear equation of the form Y=b-mX. \u00a0 By measuring the electrode potential of two or more standards of known pH you can determine E’ and the slope. \u00a0 We will use three standards and linear least squares to do this analysis. \u00a0Most pH meters perform this analysis automatically using the built in calibration procedure. \u00a0 Our task is to evaluate the effectiveness of this calibration procedure in the context of real pond samples.<\/p>\n

Please refer to The Theory of pH Measurement<\/a> datasheet for more practical considerations of pH measurement.<\/p>\n

Analytical tasks:<\/strong> (You may collect data in pairs)<\/p>\n

    \n
  1. Calibrate the pH meter using the meter\u2019s calibration function (follow the directions that come with the meter) using three pH standards. Record the electrode potential and temperature<\/strong> of each pH standard for subsequent analysis.<\/li>\n
  2. Measure the pH of two Johnson Pond samples from different locations on the lake. Record both pH as displayed on the meter and electrode potential<\/strong>. Record the location and temperature of each sample. Why is it important to know the temperature of the sample? How do temperature effects influence your results? \u00a0How will you solve the temperature problem?<\/li>\n
  3. Use a least squares analysis procedure to calculate the pH of samples in step two using the electrode potential of three standards measured in step one. Calculate the uncertainty of each pH measurement from the uncertainties in the electrode potential and uncertainties in the least square slope and intercept. \u00a0How well does the pH display of your meter represent the analytical uncertainty of the pH measurement?<\/li>\n
  4. Report the results from tasks 1-3 using the Analytical Chemistry guide to authors. Every student should have his or her own write up. \u00a0Please limit your writeup to two pages. \u00a0 Include title, introduction, methods, discussion, and citation sections in your writeup. \u00a0 Use tables or figures as appropriate to describe your methods and results.<\/li>\n<\/ol>\n

    The following is the grading scheme used for this writeup.<\/p>\n

    40 %. General Style\u00a0 – Does the report conform to the ACS \u2013 Analytical Chemistry guide to author\u2019s style?<\/p>\n

      \n
    1. Title\u00a0 – informative, including key words related to the topic<\/li>\n
    2. Authors \u2013 your name<\/li>\n
    3. Abstract \u2013 not necessary for this short work.<\/li>\n
    4. Introduction \u2013 a short introduction to the analytical problem, past analytical work relevant to the problem (with citations), and a overview of the work described in this paper.\u00a0 Often the introduction is used to detail the theory behind the analytical method.<\/li>\n
    5. Methods \u2013 a description of all methods use in the work described at a level so that an expert could reproduce the experiment using this work and other work referenced by this work.\u00a0\u00a0 Figures of a new<\/strong> apparatus or tables of reagents should be included in the methods.<\/li>\n
    6. Results\/conclusions\/discussion \u2013 often combined for short papers.\u00a0\u00a0 A complete description of the results and significance of this work.\u00a0\u00a0 Figures showing instrument response (not linear data<\/strong>) and data tables listing experimental results are located in this section.<\/li>\n
    7. Citations \u2013 you will always have one or more citations<\/li>\n<\/ol>\n

      \u00a020% Quality of written work \u2013 the lab report should be written in complete sentences, without spelling errors, and written in a clear and concise style.\u00a0\u00a0 Avoid a conversational voice in your writing.\u00a0 Focus on the completed procedures and results of the work instead of a narrative of your afternoon in lab.<\/p>\n

      \u00a040 % Answers to the specific questions should be addressed in the lab write up. \u00a0Did you perform the analysis of the data correctly?<\/p>\n

      \n<\/div>\n","protected":false},"excerpt":{"rendered":"

      The goal of this lab is give you experience reading technical manuals for standard chemical analysis, interpret these manuals in the context of your particular analytical application, and communicate your analytical results in a complete and succinct report. Background: \u00a0We … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":184,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"open","template":"","meta":{"ngg_post_thumbnail":0,"footnotes":""},"_links":{"self":[{"href":"https:\/\/web.colby.edu\/ch331public\/wp-json\/wp\/v2\/pages\/160"}],"collection":[{"href":"https:\/\/web.colby.edu\/ch331public\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/web.colby.edu\/ch331public\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/web.colby.edu\/ch331public\/wp-json\/wp\/v2\/users\/184"}],"replies":[{"embeddable":true,"href":"https:\/\/web.colby.edu\/ch331public\/wp-json\/wp\/v2\/comments?post=160"}],"version-history":[{"count":6,"href":"https:\/\/web.colby.edu\/ch331public\/wp-json\/wp\/v2\/pages\/160\/revisions"}],"predecessor-version":[{"id":466,"href":"https:\/\/web.colby.edu\/ch331public\/wp-json\/wp\/v2\/pages\/160\/revisions\/466"}],"wp:attachment":[{"href":"https:\/\/web.colby.edu\/ch331public\/wp-json\/wp\/v2\/media?parent=160"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}