NAME_______________________________SECTION LETTER____DATE_________
CHM 152L - LAB ASSIGNMENT II
One of the primary goals of CHM152L is developing the ability to critically interpret experimental results. The second week of the semester you will start work on the synthesis of an iron salt. After the iron salt is made and purified it will be analyzed to determine the empirical formula during the course of the semester as extensions to other experiments. The synthesis, purification, and analysis of a chemical product are a very common task in industry and research and are usually done by groups or teams. Each member (or members) of the team is assigned a different portion of the task. A similar organizational design will be used to analyze the product from the first experiment in CHM152L.
Form a group of up to 6 students according to lab benches. Work as a group to solve the following problem and answer the questions posed below. It is assumed that every student can do these types of calculations and manipulations so review them!
List Names of Team Members____________________________________________
1. Each group devise and carry out a procedure that provides data or demonstrates to the TA to prove that each member can use a 5 or 10 mL volumetric pipet and read the buret and thermometer. Calibrate the pipettors in your work area using the same procedure used in experiment 1 of CHM151L. Your TA will demonstrate the use of the pipettors.
Balance and vials are available.
2. The objective of this problem is to determine the empirical formula of Nax(S2O3)y·zH2O. You will need to determine x, y, and z using the following experimentally determined percent by mass results:
% Na = 13.85, 18.66, 29.39
% S2O32- = 45.95, 45.91, 46.10
% H2O = 34.65, 32.97, 34.91, 34.75
a. Determine the best percent for each component:
b. Do the three percents add up to 100%?
c. Calculate the empirical formula and the molecular mass:
d. Are there any problems with this data? Which component has the best data? Poorest Data? Why?
e. What additional experimental work would you do to get an improved result?
f. What is the percent Na in the compound if 9.330g were found in 50.001g of a sample of the compound:
3. Calculate the following values for NaCl:
a. The molecular or formula mass:
b. The moles or mol in 1.000g of the compound:
c. The molarity (M or mol/L) if 1.000g is placed in a 100mL volumetric flask, dissolved in water, and water added to the calibration mark and mixed:
d. The solution from "c" is diluted by pipetting 5.00 mL into a 100mL volumetric flask and water added to the calibration mark and mixed. What is the molarity? (hint use M1V1=M2V2)
e. How many grams of NaCl are there in 10.00 mL of solution from "d" above?
4. GRAPHING ASSIGNMENT: Using the Data Acquisition program (“Logger Pro” by Vernier) on a computer in room 228 make a temperature versus time plot following the suggestions of your TA. Open the program by double click on the icon “Chemistry Applications” on the desktop or go to “Start”, “Programs”, “Chemistry Applications” and then click on “CHM152L-B Calorimetry”. Now modify the graph by changing the scale on each axis so that the graph will provide the best data possible for time and temperature. Save this graph on your “Z” drive and close Logger Pro. Open the file again using Logger Pro and print it. Attach the plot to this sheet
5. Calculator Check: on your calculator add 1.000000000 + 1.510234892 = ___________
The answer should be 2.510234892. If not you need to select mode and change the digits display on your calculator to “Float 12” or the largest number digits your calculator will allow. If you’re having trouble resetting your calculator, get help from your TA.
6. MSDS Quiz (If not done in CHM151L): Go to the web: http://jan.ucc.nau.edu/~jkn/Labs.html
Note that you can check your grades from this web page. See what information is in the CHM152L site such as the syllabus. Click on back to get to the above location. Next, click on safety. Investigate the types of information available on this web site. Click on "Quiz" and take the on-line safety quiz. Complete the entire quiz and print the "Certificate of Achievement" with you name filled in. Turn in the "Certificate of Achievement" to your TA before you leave or at the start of the second lab period.
NAME_______________________________SECTION LETTER____DATE_________
CHM152L LAB EXERCISE
In CHM152L pipettors and the buret will be used extensively. You will calibrate both the 5 and 10 mL pipettors (as was done in CHM151L, exp. 2) and the buret to insure that you know how to use them and to make sure they are calibrated correctly. You may also wish to calibrate your volumetric pipets if you intend to use them.
First make sure all your glassware is clean and rinsed with distilled water. To calibrate your volumetric pipets, pipet the volume called for into a preweighed vial/cap. Reweigh the vial to determine the mass of distilled water delivered. Measure the temperature of the water and use the density chart posted in the lab to determine the density of water. Using the density of water in g/mL, convert the mass to a volume. If the volume calculated from the mass of water delivered is not within 0.05 mL of the desired volume check with your TA. Now do the same with the buret only try to deliver 10.43 mL.
Pipettor Pipettor 10.43 mL
10.00 mL 5.00 mL From Buret
Mass Vial&Cap (g) ____________ ___________ __________
Mass Vial&Cap&Water (g) ____________ ___________ __________
Temperature (°C) ____________ ___________ __________
Density Water (g/mL) ____________ ___________ __________
Volume (mL) ____________ ___________ __________
Get help from your TA if you volumes are not close to what they should be.