ࡱ;  R FACompObj\WordDocumentf!ObjectPoolAA  FMicrosoft Word 6.0 DocumentNB6WWord.Document.6;  Oh+'0& , 8 DPX `l LScience F:Applications:Microsoft Office:Microsoft Word 6:Templates:chem labLAB: TITLE OF LABsciencescience'@pxI@@ܥhO e'f!> 4VVVVVn xV: V       & X ~:  @:   6 >Lab: MEASUREMENT OF pH WITH ACID-BASE INDICATORS  Introduction There are three objectives in this acid/base lab: 1. To prepare a set of pH indicator standards. 2. To determine the pH of an unknown solution. 3. To find the equilibrium constant, Ka, of a weak acid. MATERIALS: a deep well plate methyl orange indicator 0.1 M HCl distilled water thymol blue indicator 4 micro medicine droppers methyl red indicator 1 M solutions of 2 different weak acids Procedure 1. This experiment will utilize the first 5 wells of 3 separate rows of the well plate. Make sure the well plate is clean and dry before you begin. 2. Using a clean medicine dropper, place 10 drops of 0.1 M HCl in well #1 of each row. Using a clean medicine dropper, place 9 drops of distilled water in wells 2 - 5 in each row. 3. Using a clean medicine dropper, transfer one (1) drop of acid from well #1 to well #2 in row 1. Repeat this procedure for rows 2 and 3. 4. Draw the entire contents of well #2, row 1 into the medicine dropper and return the contents to well #2, row 1. Repeat this procedure for well #2 in rows 2 and 3. 5. Continue this dilution procedure for wells 2 to 3, 3 to 4, and 4 to 5 in each of the 3 rows. 6. To each solution in row 1, add 1 drop of thymol blue indicator and record your results in the table provided. 7. To each solution in row 2, add 1 drop of methyl orange indicator and record your results. 8. To each solution in row 3, add 1 drop of methyl red indicator and record your results. 9. To 3 clean wells, add 10 drops of unknown acid A. To the first well sample add 1 drop of thymol blue, the second well add 1 drop of methyl orange and the the last, 1 drop of methyl red. Record your results. By comparison with the colors obtained in the standard samples , determine the pH of this unknown acid. 10. Repeat this procedure for a second unknown acid, B. 11. Clean all materials and return them to the appropriate places. Data STANDARD SAMPLES INDICATORS12 345THYMOL BLUEMETHYL ORANGEMETHYL RED CONCENTRATIONPHUNKNOWN ACIDS THYMOL BLUEMETHYL ORANGEMETHYL REDPHUNKNOWN ACID #1UNKNOWN ACID #2 Calculations 1. a. Calculate the pH of the standard solutions prepared in steps 1 - 8. Enter the values in the data table. What effect does a dilution by a factor of 10 have on the pH of an HCl solution? b. Estimate the pH range over which each of the indicators changes color. State the color of the form present at low pH and at high pH. 2. a. What was [H+] in the sample of 1.0 M weak acid #1 whose formula you may take to be HA? b. What was [A-]? What was [HA]? c. Substitute the concentration values from parts a and b into the Ka expression and calculate the value of Ka for acid #1. d. Repeat steps a - c for acid #2. e. Assume that a salt of the weak acid, such as NaA, is added to the weak acid solution. Using LeChateliers Principle, explain the effect that this would have on the [H+] and the pH of the solution. Analysis Write a conclusion based on your experimental results. ACIDS/BASES Name: _______________________ Partner #1: _______________________ Partner #2: _______________________ Acton-Boxborough Regional High School Due Date: ______________________ Acton-Boxborough Regional High School  |HH(EG(HH(d'`|HH(EG(HH(d'` |HH(EG(HH(d'`00&ta0`0(00&00&00&00&00&ࡱ; SummaryInformation(@Microsoft Word 6.0.14; 6789:H 8 F =>I"&'uU]cU]cU]]^]uD]a UZ]c( UZ]c($79GHz{!,-Yu;n?3 k $$$,$,$$$$$$$$$$$$$$,$,$$$$ddh)               ) * + , - . / 2 3 4 5 6 7 8 dddddddddddddddddddddddddddddddddddddddddl  H$)8 F G H T b m p q  q r s ^ _ '$$$$$,$,$$$$$$$$$$$$$$hl $''(>h$%&'$$$$$$$$$$,$,$$$T$T$ 0 !l h !s0h !shK@Normal]a "A@"Default Paragraph Font @ Header ! @ Footer !*O"* Chem HeaderL UZ]c' '9FX?8' u  8 '' 79 ' 4d>science3Science F:Teacher Folders:Murphree:pH/Ka/INDICATORS@   >VMTimes New Roman Symbol MArial MTimesMNew Century Schlbk"1h999!~KScience F:Applications:Microsoft Office:Microsoft Word 6:Templates:chem labLAB: TITLE OF LABsciencescienceࡱ;