Please help with my chemistry lab. I have include the lab notes to help with the lab hw. The 4d rule lab note is to help with the lab question on page 11 and 12
kuromi
chemlab9.pdf
Lab Station: _________ Name: _____________________
CHEMISTRY 180
LABORATORY EXPERIMENTS
Part III
ORANGE COAST COLLEGE
Spring 2020
By W. Roundy, S. Ashbaugh, S. Johnson and J. Wylie
Edited by A. Vieau, S. Gonzales, H. Maughan, M. Laux, R. Frechen
Please leave the this lab book in the lab room at all times. Removal of the lab book from the lab will result in a loss of points. Lab Section: MW or TuTh Time: __________ Circle one. Fill in.
1 Lab Score: ______ Unknown Score: ______
STANDARDIZATION of NaOH EVERY DAY: When you are finished with the buret for the day, rinse the buret four times with DI water, and fill the buret to the very top with DI water. Release the pressure from the tip by delivering a little DI water while inserting the cork. There should be no air space left in the buret. Ask your instructor to check the buret(s) and sign below. Points will be deducted for failure to obtain initials. Date Initials Date Initials Date Initials ______ _________ ______ _________ ______ _________ ______ _________ ______ _________ ______ _________ This experiment involves the preparation of a standard oxalic acid solution and a base solution, aqueous sodium hydroxide. The sodium hydroxide solution will be standardized using solid potassium hydrogen phthalate, a primary standard acid. These solutions will be used in later experiments for the titration of an unknown acid solution and possibly an acetic acid solution. The accuracy of the calculated molarity for your unknown acid depends on the accuracy of the molarities (or normalities) of the standard solutions prepared in this experiment. Read the Analytical Techniques in the GCN. You will use several of these methods during this experiment. Consider the calculated concentrations as intermediate values. Carry two extra nonsignificant digits in the molarity (or normality) values. Calculations should be set up using the unit equation (dimensional analysis) approach. Part I: Preparation of a Standard Oxalic Acid Solution Anhydrous oxalic acid is not readily available, but oxalic acid dihydrate, H2C2O4.2H2O, can be purchased. Oxalic acid dihydrate does not meet the requirements of a primary standard and should not be used as a titrant without first being standardized. However, because only small volumes of low concentration oxalic acid will be used, it is an acceptable standard for our purpose. Write the balanced molecular, complete ionic and net ionic equations for the reaction of sodium hydroxide solution with oxalic acid solution.
Calculate the mass (g) of oxalic acid dihydrate required to prepare 250.0 mL of 0.0300 N H2C2O4.
2 From your instructor, obtain a test tube containing the approximate amount of oxalic acid dihydrate needed to prepare the solution. Obtain a 250.0 mL volumetric flask and powder funnel from the cabinet in the front of the lab. Use all of the sample that will come out of the test tube with tapping. Using the Analytical Techniques described in the GCN, carefully prepare 250.0 mL of standard oxalic acid solution. ______ water will be used to prepare this solution. Record the masses that will be used to calculate the mass of oxalic acid dihydrate in the table below. DATA TABLE Part I initial mass of test tube containing oxalic acid dihydrate ______________
final mass of test tube ______________
mass of oxalic acid dihydrate dispensed ______________ Use the actual mass of oxalic acid dihydrate that you placed in the 250.0 mL volumetric flask to calculate the normality of your standard oxalic acid solution. In r c or Ini ial _______________ Transfer the standard oxalic acid solution to a properly prepared 250 mL plastic bottle for storage and later use. Return the test tube to your instructor. Keep the lid on the storage bottle as much as possible. Part II: Preparation of the Sodium Hydroxide Solution Calculate the volume (mL) of 6.0 M NaOH solution required to prepare 1.0 L of 0.09000 N NaOH solution. In r c or Ini ial _______________ Rinse your 1 L plastic bottle four times with 5 mL DI water. Use your 50 mL graduated cylinder to add the calculated volume of 6 M NaOH to the plastic bottle. Add DI water to the bottle until the level is at the shoulder of the bottle. (You may fill with DI water from the DI tap if you are careful to keep the plastic tubing on the spout above the top of the bottle.) Cap the bottle, invert and mix 25 times. This solution should be kept tightly covered: Carbon dioxide in the atmosphere reacts with the hydroxide ion in the solution changing the concentration of the sodium hydroxide in the solution.
3 Part III: Preparation of Potassium Hydrogen Phthalate Samples Potassium hydrogen phthalate, KHC8H4O4, is often abbreviated as KHP. Note that KHP is not the formula! KHP is a monoprotic acid that can be obtained with a high level of purity. Its high purity, relatively large molar mass, and stability make KHP an appropriate substance to use as a primary standard. Potassium hydrogen phthalate is commonly used to standardize sodium hydroxide solutions. KHP molar mass: _____________________ KHP eq mol 1: ___________________ The e h d f Weighing by Difference will be used to weigh out four samples of KHP with approximate masses between 0.6 g and 0.8 g. The precise mass of the samples should be obtained by difference using measurements from an analytical balance (a.u. = 0.0001 g). The mass of the samples should differ from each other by at least 0.01 g. Weighing b Difference (in the GCN) is a two-balance method you will use to analytically transfer your samples of KHP to Erlenmeyer flasks. Answer the following questions. Wha bjec i aced he ade a : What mass is measured on the top loader balance (Why?): What object is placed on the pan of the analytical balance: What mass is determined on the analytical balance (Why): Why is it important not to weigh the top loader object on the analytical balance? Obtain a set of two burets on a buret stand from the shelf in the middle of the lab bench. Choose the buret set that has the same number as the last two digits of your lab station. Using proper conditioning techniques, prepare a buret for use in delivering your sodium hydroxide solution. Be sure there are no bubbles in the tubing or the buret tip. The first titration will be performed without any back-titration. The first titration will be primarily to determine the approximate volume of NaOH solution needed to get to the end point, and to gain some experience in titration. During these titrations, when will you reach the endpoint if you forget to add the indicator? _____________ Would you reach the equivalence point? ______________ In r c or Ini ial _______________ From your instructor, obtain a test tube containing enough KHP for several titrations. Prepare four clean, but not necessarily dry, 250 mL glass Erlenmeyer flasks (lab locker). Dry the flasks on the outside, then number them in pencil 1, 2, 3, and 4. Understand the technique before weighing out any sample. Record the data for the first two samples of KHP in the data table on the next page, but keep the test tube with the remaining KHP in your drawer for additional runs later. If any mass is lost from the test tube and does not go into the flask during the transfer, the mass of KHP will be incorrect and that sample should be discarded. Your hands should be dry when handling the test tube and flasks.
6 Part VI: Standardization of NaOH Solution with Solid KHP Including Back- Titration with a Standard Solution of Oxalic Acid For these titrations, your standard oxalic acid solution will be used to back-titrate the reaction mixture. Refill the NaOH soln buret as usual. Prepare the second buret by rinsing it four times with 5 mL portions of your standard oxalic acid solution. Place between 10 and 15 mL of your standard oxalic acid solution in the second buret. Remember to record both initial and final volumes in the data table below. You may want to label the buret stand with A for acid and B for base. Keep the storage containers adjacent to the appropriate buret to prevent refilling a buret with the wrong solution. Prepare Flask #3 as before. Titrate the KHP with your NaOH solution. Intentionally titrate past the endpoint, back-titrate with the oxalic acid solution, then re-approach the endpoint by adding NaOH solution. Use a minimum of 1.00 mL of back-titrant. For the final approach to the endpoint, titrate very carefully. Repeat as often as necessary. Refill the NaOH soln buret with your solution and repeat the procedure with Flasks #4, #5 and #6. The goal is to have the normalities (from Runs #3 through #6) of three, preferably consecutive, titrations with an extreme relative deviation of 1 ppt or less. This will most likely take more practice in Part VII. The extreme relative deviation is just the absolute deviation between the lowest and highest values, divided by the highest value (multiplied by 1000 to get ppt). This is a measure of precision (or consistency), which has a direct correlation with the confidence we have in your technique. DATA TABLE for Part VI sample number 3 4 5 6
initial mass of tt + KHP _________ _________ _________ _________
mass of tt sample _________ _________ _________ _________
mass of KHP in flask _________ _________ _________ _________ sodium hydroxide solution
Buret # and letter: _________ _________ _________ _________
final buret reading _________ _________ _________ _________
initial buret reading _________ _________ _________ _________
volume NaOH delivered _________ _________ _________ _________ oxalic acid solution Buret # and letter: _________ _________ _________ _________
final buret reading _________ _________ _________ _________
initial buret reading _________ _________ _________ _________
volume oxalic acid delivered_________ _________ _________ _________ normality of NaOH solution _________ _________ _________ _________
7 Calculate the normalities of your NaOH solutions for Flasks #3 through #6. RUN #3: RUN #4:
8 RUN #5: RUN #6:
11 Part VIII: Result Analysis A.1. Enter five calculated normalities (exclude #1) for your sodium hydroxide solution below. Include
two non-significant digits and the dashed line. ____________ ____________ ____________ ____________ _____________
Order the normalities from the smallest to the largest.
____________ < ____________ < ____________ < ____________ < _____________ Circle the most extreme value (the outlier). You may be able to discard this value, but you can only
discard values by showing that the value is statistically different from the other values. Refer to the GCN, and see if the 4-d rule can be applied to eliminate this value. The steps are below:
2. Calculate the mean for the four results that agree best with each other. If you have three values with an extreme relative deviation of 1 ppt or less, you may use those three values instead of four. 3. Calculate the average absolute deviation from the mean for the four (or three) values from A.2. 4. Multiply the above average absolute deviation by 4.
12 B. Calculate the absolute deviation of the next closest result, he ie (the one circled in A.1.) from
the mean value of the best results (from A.2.) C. Which is the larger A.4. or B.? (Circle one.) If B is larger, you may statistically eliminate the worst result. Put a single line through the column
of data in your data sheet and note that it was eliminated using the 4-d rule. If A.4 is larger, you must use all of the values and will need to recalculate the average normality, the average deviation and the rad in ppt. Attach a separate sheet showing the calculations.
Record the average and the average deviation you will use for your results of this experiment. avg normality ________________ avg deviation: ________________ D. Determine the relative average deviation (in ppt) of any remaining values.
I c I i ia : __________ If your rad is larger than 2 ppt (0.8 ppt for A work) you should titrate more samples of KHP. After completing the additional titrations, repeat the process of analyzing your results. If your RAD is still larger than 2 ppt, take your bottle of NaOH solution and your clean, dry 250 mL storage bottle to your instructor and exchange it for a standardized NaOH solution (10 pt deduction!). When you are finished with the standardization lab, place the KHP test tube and stopper in the labeled container. Save the standardized NaOH solution (yours or ours) for the next experiment.
Average Normality of NaOH for the next experiment: ___________________
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