CHEM 1953 Final: Lab Exam Study Guide
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Using this information: I used 4.00 g potassium dichromate. The amount of Iron ll is 4.00 gram in 2nd flask. Used grey moose vodka 2.00 ml and filled flask with water. This was the 2% vodka solution. For the experiment I used 5.00ml of the vodka and added 35.00 ml of more water to make it 1/8 of 2% or 0.25% of the original. With this information and the answer's i have placed in the table please help with remainder of questions. Need to work to understand answers so I will get correct on upcoming test. Thanks.
Calculate the concentration of the dichromate ion in the first volumetric flask.
Calculate the concentration of the iron (II) ion in the second volumetric flask.
Experiment 2: Titrate the Vodka Sample
Lab Results
Record the following lab data in the table below. If you had to repeat one of the titrations, disregard the value that was different.
(a) volume of potassium dichromate solution added to the Erlenmeyer flask in mL | 5.00ml |
(b) coarse titration volume of iron (II) solution range in mL | 14.10 -14.15 ml |
(c) volume of iron (II) solution delivered from the burette in mL during the first fine titration | 14.13ml |
(d) volume of iron (II) solution delivered from the burette in mL during the second fine titration | 14.11ml |
(e) average volume of iron (II) solution used in the fine titrations | 14.12ml |
(f) the color of the analyte solution at the end point of the titration | purple |
(g) the color of the analyte solution after adding the indicator | dark green |
Data Analysis
Record and calculate the quantities in the table below using the data from your dichromate titrations. Use an average value for the volume of iron (II) solution used in the titration. If one of your values is very different, and you had to perform the titration three times, disregard the value that was very different when computing the average.
(a) volume of potassium dichromate solution added to the Erlenmeyer flask in mL 5.00ml | |
(b) moles of dichromate ion added to the Erlenmeyer flask | |
(c) average volume of iron (II) solution delivered from the burette in mL 14.12ml | |
(d) moles of iron (II) ions delivered from the burette | |
(e) moles of excess dichromate ions that reacted with the iron (II) ions (remember that the ratio in which they react is 1 dichromate : 6 iron (II)) | |
(f) moles of dichromate that reacted with the ethanol in the vodka (Subtract excess dichromate ions that reacted with the iron (II) ions from the original moles of dichromate ion present.) | |
(g) moles of ethanol in the 5 mL diluted vodka sample according to the stoichiometric ratio of 2 dichromate ions to 3 ethanol molecules |
The amount of alcohol in a drink is typically reported as percent alcohol by volume. Volume percent or volume/volume percent (% v/v) most often is used when preparing solutions of liquids. Volume percent is defined as:
% v/v = Vsolute/Vsolution à 100
Find the percent alcohol (ethanol) by volume for the vodka used in the lab by following the steps outlined in the table below.
(a) given the molar mass of ethanol of 46.07 g/mol, calculate the mass of alcohol (ethanol) in the tested sample solution | |
(b) given the density of ethanol of 0.7893g/ml, find the volume in mL of ethanol present in the diluted vodka solution | |
(c) record the volume of vodka used in the experiment in mL | |
(d) find the percent alcohol by volume (% v/v) in the diluted vodka solution | |
(e) the diluted vodka solution was prepared by diluting 2.00 mL vodka to 100.00 mL. Calculate the dilution factor used (N:1) | |
(f) multiply the percent alcohol by volume in the diluted vodka solution by the dilution factor to obtain the % v/v alcohol in the original vodka solution |
Conclusions
The Grey Moose vodka tested in this lab reports a percent alcohol by volume of 40.0% on its label. How does your value compare to the reported one? If the values are different, give one possible experimental error that might have contributed to the difference.
Potassium permanganate is another strong oxidizing substance similar to potassium dichromate. An acidic solution of purple permanganate ions can get reduced to colorless Mn2+ ions in the presence of ethanol. Write down the redox reaction between permanganate and ethanol, and balance it using the half-reaction method.
Besides vodka, there are other colorless alcohol-containing beverages that can be titrated following the procedure in your lab. Given the average values for the percent alcohol by volume listed in the table below, which beverage do you expect to use the least amount of iron (II) standard solution during the titration? Assume all lab procedures stay the same.
% alcohol by volume | |
White rum | 37.0% |
Vermouth | 18.0% |
White whine | 12.0% |
1-How many grams of NaCl would be needed to prepare 150.00 L of a 1.402 M NaCl solution?
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2- first a standardized solution of sodium hydroxide (NaOH) will be quantitatively diluted to about 0.1 M but not exactly 0.1M. The molarity of the dilute NaOH will be calculated! A similar quantitative dilution was done in experiment 3 when you diluted 5.0 M HCl to 0.50M HCl using a volumetric flask and pipet.
The second part of the experiment is very similar to the last part of experiment 6 where samples of the unknown were weighed out, dissolved in water, and titrated with the dilute NaOH using phenolphthalein as the indicator to determine the percent by mass of a compound in the unknown. The compound will be different than the compound used in experiment 6. The molecular formula of the compound will be provided during the final. You must know how to weigh by difference (Preweigh, tare sample and small container to zero, transfer sample to flask, and place the small container back on balance to get mass) and titrate the sample using the buret in order to do well.
Be sure to read the instructions for the practical toward the end the CHM151L lab manual and do the practice problem on the next page.
You will have 1.5 hours to do the practical. You may only use a calculator and a pencil on the practical. There is no talking during the practical such that students cannot help each other and the TA may only help you with equipment problems.
It would be a good idea to wash any glassware you might use the lab period before the lab practical. There will also be a help session before the lab practical.
At the end of the lab final you will wash all glassware used or any dirty glassware in your locker, wash your unknown vials and remove the labels, checkin your locker and return your key, and evaluate the lab.
Please put the following statements in the correct order relating to the day of the lab practical:
1 2 3 4 5 6 Wash all your glassware and unknown vials, checkin your locker, evaluate the lab, and check your grades.
1 2 3 4 5 6 Do at least 3 good trials (weigh and titrate sample) as time allows.
1 2 3 4 5 6 Start the lab practical by diluting the NaOH solution.
1 2 3 4 5 6 Before the day of the practical clean glassware, read the practical instructions and do the practice problem in the lab manual and complete the loncapa problems for the final.
1 2 3 4 5 6 Calculate the molarity of the dilute NaOH, the percent by mass of the compound in you unknown for each trial and then the median.
1 2 3 4 5 6 Come to the help session before the lab final.
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3-
A NaOH solution was prepared by diluting 5.00 mL of 2.205 M NaOH to a final total volume of 100.00 mL. What is the exact molarity of the dilute NaOH (use 4-5 significant figures)?
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4-For the problem above, select glassware and size from the list below to conduct the dilution.
A | Amber Bottle |
B | Mohr pipet |
C | Buret |
D | Volumetric Flask |
E | Volumetric Pipet or Pipettor |
F | Graduated cylinder |
G | Erlenmeyer flask |
H | Beaker |
A B C D E F G H <= Glassware used to transfer the 2.205 M NaOH to be diluted
A B C D E F G H <= Glassware used to measure the final volume of the diluted M NaOH.
5 10 15 20 25 50 100 250 500 1000 <= Volume of the glassware chosen to transfer the concentrated NaOH above
5 10 15 20 25 50 100 250 500 1000 <= Volume of the glassware chosen to contain the final dilute NaOH above.