Experiment #3. Graphing with Excel

Transcription

1 Experiment #3. Graphing with Excel Study the "Graphing with Excel" instructins that have been prvided. Additinal help with learning t use Excel can be fund n several web sites, including menu.html. The "help" functin f Excel als can be useful t answer specific questins. Nte that Excel can eliminate the need t make manual calculatins fr example, in this exercise, instead f using a calculatr t find the natural lg (ln) values, simply type the fllwing in the cell where the ln data is t be put: =ln(x1), where x is the clumn and 1 is the rw f the cell cntaining the data yu want t take the natural lg f. Similarly, t btain the reciprcal f the temperature data, simply type the fllwing in the cell where yu want the reciprcal: =1/x1, where x is the clumn and 1 is the rw f the cell cntaining the temperature data yu want t take the reciprcal f. Yu can use the cut and paste functins t cpy frmulas such as this int the ther cells in the clumn s yu dn't have t retype the frmula each time Excel will autmatically enter the crrespnding VP r T data frm the same rw. If yu take sme time t practice, Excel can becme a very pwerful tl fr yu. Relatinship f Vapr Pressure t Temperature: Develping the Clausius- Clapeyrn Equatin 1. Type in the temperature and vapr pressure data fr Tluene (clumns 1 and 2) int an Excel spreadsheet as seen belw. Label the tp cell in each clumn and include that cell when yu plt the data. T ( C) VP (Trr) T in K 1/T in K VP (Trr) ln (Vapr Pressure) (A) Make clumn 3 by cnverting the temperature in clumn 1 int Kelvin. (B) Make clumn 4 by taking the inverse f the temperature in Kelvin (1/T). (C) Cpy clumn 2 int clumn 5. (D) Make clumn 6 by taking the natural lgarithm (ln) f the VP in Trr. (clumn 5) 3. Yu will be making a series f XY scatter plts. Temperature in sme frm will be the x axis and Vapr Pressure in sme frm will be the y axis. The gal is t find a mathematical relatinship between the x and y data. In chemistry we like straight lines. If the plt yields a straight line then the equatin: y = mx + b can be used. T generate a graph in excel, select the clumns yu want t plt by dragging the cursr while hlding the cntrl buttn (r cmmand buttn n Macs). Excel will autmatically plt the left- hand clumn n the x- axis and the right hand clumn n the y- axis. In this exercise, be sure that yur selected temperature data is n the left side f yur VP data, therwise yur graph will be inverted. This is why we repasted the VP data after the temperature data in ur table.

2 Once the apprpriate data are highlighted, chse the type f graph yu want t generate in Excel. In this class we will always graph using the Marked Scatter Plt ptin in Excel. D nt chse plt ptins that have lines. When we want lines n ur Excel graphs we will add them using the trendline feature. Yu are nt finished! The graph autmatically generated by Excel is never crrectly frmatted fr submissin in a science curse. Belw are features f a gd graph. Be sure any graph yu turn in fr this class adheres t these guidelines. Each versin f excel has different ways t change graph frmatting. If yur versin is different frm the ne in the lab vide n the CHM112 website, yu may need t use yur help buttn t learn hw t make these changes. Give the graph a descriptive title. Dn t just repeat the infrmatin in the axes titles. Pressure vs Temperature fr what? Lk in the instructins abve t find what substance this data is fr. Yur title shuld describe what the experiment was abut. Label axes with the type f unit and the unit itself. Fr example: Temperature ( C). Axes shuld be at the bttm and left f the graph nt in the middle f the data. Remve the legend if it prvides n infrmatin. Mst Excel versins default t having legends fr every graph. If yu are nly pltting ne set f data per graph, the legend cntributes nthing get rid f it. Change the start and end pints f each axis s that the data takes up the majrity f the graph. Excel usually defaults t having bth axes start at zer. This ften leads t the graph having a lt f white space, which we d nt want. Change the minimum value f each axis s that it starts just belw yur lwest data pint. Add a trendline when apprpriate. If yu want t find a mathematical relatinship in the data, be sure t include a trendline and t check the bx t display the equatin n the chart. Yu can als chse t display the R 2 value. The clser the value f R 2 is t 1, the better the fit. Yu will add trendlines t all three graphs in the exercise. Add mre gridlines when apprpriate. In this exercise we are nly cncerned with the trendline, but in sme labs yu will need t estimate a value ff the graph after printing. If this is the case, be sure t add enugh gridlines s that yu can accurately estimate yur value. If yu need t read a value t the nearest 0.1 ml, but yur x- axis nly has gridlines every 5 ml, yur estimate will be pr. Print yur graphs at a reasnable size. Usually abut ½ page is apprpriate. Als print the spreadsheet when asked. With the data in yur tables, generate and print the fllwing graphs as well as yur spreadsheet data and attach them t this lab. (A) Plt VP vs T in K. Add trendlines (bth linear and expnential) and display the equatins fr bth trendlines n the chart. (B) Plt VP vs 1/T in K. Add trendlines (bth linear and expnential) and display the equatins n the chart. (C) Plt ln(vp) vs 1/T in K. Add a linear trendline and display the equatin n the chart.

3 Name CHM112 Lab Graphing with Excel Grading Rubric Criteria Pints pssible Pints earned Graphs crrectly pltted and adhere t all guidelines (including descriptive title, prperly frmatted axes, trendline equatins displayed) Graph 1 2 Graph 2 2 Graph 3 2 Questin 1 (1 pint each part) 1 Questin 2 (1 pint each part) 6 Questin 3 1 Questin 4 1 Questin 5 (1 pint each part) 5 Ttal 20 Subject t additinal penalties at the discretin f the instructr.

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5 Graphing with Excel: Pst Lab and Analysis Name: 1. Cnsider Graphs (A) and (B) 2. a) Which trendline was a better fit, the linear r the expnential? b) What was the equatin fr the best fitting trendline fr each graph? Equatin fr Graph A: Equatin fr Graph B: 3. Cnsider Graph (C) a) Did yu btain a linear relatinship fr the data pltted? b) What was the equatin f the best fitting trendline? c) What is the frm f the Clausius- Clapeyrn equatin that we use fr graphing? (the frm that can be written as y = mx + b). d) Based the equatin fr the best fit line (the equatin fr the trendline in C), calculate the enthalpy f vaprizatin (ΔH vap ) fr Tluene in kj/ml. (R = J/ml K.) Shw yur calculatins and all units. e) Is the sign f the ΔH vap that yu calculated psitive r negative? Des this fit with what yu knw abut heat f vaprizatin? Explain yur answer (yur explanatin must be chemistry based and nt mathematical). f) Lk up ΔH vap fr Tluene in a reliable surce (like the CRC handbk f Chemistry and Physics r the NIST Chemistry webbk ( ) and NOT Wikepedia). (Include prper units) ΔH vap = Surce frm where yu btained the data

6 4. Using the equatin fr the best fit line frm Graph C, calculate the vapr pressure f Tluene at 45.0 C. Shw yur wrk. 5. Using the equatin fr the best fit line frm Graph C, calculate the nrmal biling pint f Tluene in C. Recall that nrmal biling pint means that the pressure is 760 trr. Shw yur wrk in detail. 6. Ethanl and dimethyl ether have the same mlecular frmula (C 2 H 6 O) and mlar mass (apprx 46 g/ml). a) Lk up ΔH vap fr bth these cmpunds in a reliable surce (like the CRC handbk f Chemistry and Physics r the NIST Chemistry webbk ( and NOT Wikepedia). List the values belw with the crrect units. ΔH vap fr ethanl = ΔH vap fr dimethyl ether = Surce frm where yu btained the data b) Which f the tw cmpunds has the larger ΔH vap? c) Draw the Lewis structure fr bth cmpunds. d) list the IMFs present in each e) Use yur answers in c) & d) t explain why ne f the cmpunds has a larger ΔH vap.