Calibration of Volumetric Galssware

Calibration of Volumetric Glassware

Read: Chapters 1-4 in Harris to be prepared for the laboratory experiment.

This experiment is designed to introduce you to proper analytical laboratory techniques and to the methods for evaluating analytical data. As an analytical chemist, it is imperative to gather the best possible data from your equipment. Therefore, it is important to use all equipment correctly, patiently and precisely. In addition, a good analytical chemist will calibrate an ”instrument” before they use it to assure that the data gathered is as accurate as possible.

General Guidelines for the Analytical Laboratory

1.) Never assume any glassware is clean unless you washed it yourself!!! 2.) Keep your bench area clean! 3.) Clean all glassware with soap and tap water unless otherwise directed. 4.) Use distilled water to rinse your glassware, preferably a double or triple rinse. 5.) Glassware that will not come clean in soap and water should be cleaned by soaking in a solution of 1 M Nitric Acid or 1 M KOH in alcohol, followed by a soap and water wash and distilled water rinse. This is typically true of burets. 6.) Never heat any piece of volumetric glassware. Heating will cause changes in the glassware that will cause it not to be volumetric anymore J 7.) All items in this laboratory will be massed using the analytical balance. These balances read to the nearest 0.1 mg (0.0001 g). Thus, all masses recorded must be to the nearest 0.1 mg. (Do not record anything from the balance with out all 4 places) 8.) You will be assigned a balance to use. You will use the same analytical balance for all measurements throughout the semester. This improves the precision of your measurements. (Plus I know who to penalize when it is trashed!) 9.) YOU MUST CLEAN THE ANALYTICAL BALANCE WHEN YOU ARE FINISHED WITH IT! Failure to do so will result in a 5 point deduction from the laboratory reports of all the students assigned to that balance. 10.) Burets must be washed at the end of every laboratory period (soap, water, rinsing with distilled water). Burets should be placed in the buret holder to drain— UPSIDEDOWN, with the stopcock open (MAKE SURE YOU INTIAL YOUR BURET). 11.) Label all your glassware (on the glassware itself) as you use it and you should write the labels in your notebook so that you can keep track of what sample goes with what piece of data. 1.) Refer to guidelines about keeping a notebook and writing a report in the ACS format. Procedure

Use and Calibration of a Pipet

1.) Record the temperature in the laboratory (remember significant figures, there are divisions on the thermometer!) 2.) Obtain a 10.00 mL volumetric pipet (there may be one in your drawer.) 3.) Clean the pipet so that no droplets of distilled water are left on the inside of the surface as it drains. Alcoholic KOH might be needed. 4.) Clean and dry (with paper towels) a small sample bottle with cap. 5.) Avoid touching the flask/bottle with your hands as fingerprints and oils from your hands will cause imprecision in the recorded masses. You may use Kimwipes to do this. 6.) Weigh the bottle to the nearest 0.1 mg 7.) Place the bottle on a clean, dry surface at your work station. 8.) The proper procedure for the use of a pipet appears in your textbook on page 27- 28. A few rules apply: a. Clean the pipet as directed b. Avoid sucking liquid into the pipet bulb as this causes contamination c. USE YOUR INDEX FINGER TO REPLACE THE BULB FOR DISPENSING. DO NOT UNDER ANY CIRCUMSTANCES USE YOUR THUMB!!! You cannot hold the pipet perfectly level for proper reading of the meniscus if you use your thumb. If I see you use your thumb, I will correct you. Even if it feels funny, relearn to do it the right way. d. You should always rinse the pipet with the solution you are pipetting and throw away the rinsing solution. e. Read the meniscus at eye level. f. Dry the outside of the pipet before delivery g. Never blow out the pipet, allow it to drain naturally. h. After draining, touch the pipet tip to the side of the container that you are using to ensure adequate delivery of the last drop. 2.) Fill the pipet with room temperature distilled water. 3.) Deliver the water to the weighing bottle as directed above. 4.) Cap the bottle 5.) Re-weigh the bottle. Taking care not to touch the bottle with your fingers. 6.) Repeat this procedure a minimum of 4 times. Continue to repeat the procedure until your values agree within 0.005 g 7.) Record the temperature in the laboratory. Use and Calibration of a 50 mL Buret

You will calibrate this buret and use the same buret all semester. Keep it in your drawer. The data that you take today will influence (positively or negatively) the accuracy and precision of about 75% of the rest of the experiments you perform this semester.

1.) Record the temperature in the laboratory. 2.) Wash the buret as you did your pipet and allow it to drain. Alcoholic KOH and a long handled buret brush (make sure it is a buret brush) will be useful. 3.) Close the stop cock 4.) Hold the buret in your hand and, using a transfer pipet, rinse your buret with the solution you are going to use to fill it. Here we are using room temperature distilled water. 5.) Drain completely into a beaker. 6.) Properly place the buret into the buret clamp. Be sure that the clamp is mounted tightly and is level. 7.) Use a funnel and refill the buret with your titrant. Go slightly past the 0.00 mL mark (you may need a transfer pipet to avoid over filling the buret). If any solution gets on the outside of the buret, be sure to wipe it off. 8.) Open the stopcock and drain the buret to the 0.00 mL mark. You must be at eye level with this position to read the meniscus properly. You may need a stool. 9.) Be sure that there are no air bubbles in the buret or in the stopcock tip. If there are, drain the buret slightly again to force them out and refill it. 10.) Touch the beaker to the tip of the buret to remove the hanging drop. 11.) Allow the buret to stand for 5 minutes. 12.) Record the temperature in the laboratory. 13.) Weigh another weighing bottle using the same procedure as in the Pipet section. 14.) If the level of the buret has changed, add more titrant, slowly, to reach the 0.00 mL mark 15.) Place the weighing bottle under the buret. 16.) Open the stopcock and allow ~10 mL of water to drain into the bottle. Cap the bottle to prevent evaporation. 17.) Wait 30 seconds for the film of liquid on the walls of the buret to drain. 18.) Read the buret, to the nearest 0.01mL. YOU WILL HAVE TO ESTIMATE THE LAST DIGIT. THIS DIGIT IS IMPORTANT AND SIGNIFICANT. BURET DATA RECORDED AS 10.00 mL consistently is not truthful. No one is that good. J Read what you really see. Persons who consistently turn in buret data as 10.10, 10.20, 10.40 etc will have points deducted. 19.) Weight the bottle to the nearest 0.1 mg. 20.) Repeat the procedure in ~10 mL increments, all the way to 50 mL. 21.) Refill the buret and repeat this procedure 2 more times. 22.) Record the temperature in the laboratory. 23.) Label the top of the buret with your name (use tape and a sharpie). 24.) Be sure to drain the buret upside down and stopcock open when you are through. (on rack by sink) Calculations (now the fun really begins) Pipet 1.) Calculate the average temperature in the laboratory. 2.) First you must correct all weights for buoyancy, using the density of water at the average temperature of the laboratory and the density of the brass weights used to calibrate balances, 8.00g/cm3. (Follow page 24 and 32 in Harris) Typically the buoyancy correction is not needed for very dense substances. 3.) Convert the new weight to mL using the density of water at the average temperature of the laboratory. This Table is on page 32 in Harris. 4.) Calculate the average volume of water delivered by your pipet. You may use the Q-test to see if any of your data can be rejected. 5.) Calculate the standard deviation of your measurements. 6.) Calculate the relative standard deviation of your measurements. 7.) Does your pipet meet the specified tolerances listed in table 2-4? 8.) What is the probable true value of the volume delivered by the pipet at the 95% confidence level? Buret 1.) First you must correct all weights for buoyancy, using the density of water at the average temperature of the laboratory and the density of the brass weights used to calibrate balances, 8.00g/cm3. (Follow page 24 and 32 in Harris) 2.) For the buret, the calculations are slightly different. Follow this example: a. For this example, the laboratory temperature is 24ºC b. Convert the new weights to mL using the density of water at the average temperature of the laboratory. This Table is on page 32 in Harris. c. Treat each volume interval (0-10; 10-20; 20-30; 30-40; and 40-50) separately. For each volume interval, you have 3 trials. Final reading10.01 mL 10.06 mL 9.97 mL Initial reading0.00 mL 0.02 mL 0.01 mL Difference10.01 mL 10.04 mL 9.96 mL Mass10.025 g 9.986 g 9.985 g Actual Volume10.05 mL 10.01 mL 10.01 mL Correction+0.04 mL - 0.03 mL + 0.04 mL Averagecorrection for interval 0-10 mL = + 0.02mL The buret delivers 0.02mL more than indicated by the buret reading. You would add0.02mL todata recorded within thisinterval. 3.) Calculate the standard deviation of your correction measurements at each interval and one overall correction standard deviation for the entire buret. 4.) Calculate the relative standard deviation of your measurements. 5.) Does your buret meet the specified tolerances listed in table 2-2? 6.) What is the probable true value of the volume delivered by the buret, at each interval, at the 95% confidence level? 7.) Average the 3 sets of correction values (0-10, 10-20, 20-30, etc) together Prepare a calibration curve of Average Total Correction Volume vs. Total mL delivered. To do this, you will need to add each of the 10 mL intervals together. First, plot the average of the corrected volumes for the 0-10 mL at the 10 mL point on the graph. Then, add the 0-10 mL corrected volume plus the 10-20 mL corrected volume interval and plot this number at 20 mL on the graph. Then add in the next interval, from 20-30 and calculate that average corrected volume at 30 mL repeat until you finish the entire 50 mL. Keep a copy of this graph and refer to it for every subsequent laboratory experiment using your buret. In order to use the curve, you must start all titrations at 0.00 mL.

Density of Water (Data from table 2-7)

Temperature (°C) Density (g/mL) Corrected volume of 1 g of water at 20(°C)* (mL)

19 0.9984082 1.0027 20 0.9982071 1.0029 21 0.9979955 1.0031 22 0.9977735 1.0033 23 0.9975415 1.0035 24 0.9972995 1.0038 25 0.9970479 1.0040 26 0.9967867 1.0042 *Corrected for buoyancy and expansion of borosilicate glass