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Combustion analysis of a compound known to contain just C, H, N, and O demonstrated that it is 46.21 wt% C, 9.02 wt % H,13.74 wt% N, and, by difference, 100 - 46.21 - 9.0213.74 = 31.03 wt% O. This means that 100 g of the unknown would contain 46.21 g of C, 9.02 g of H, and so on. Find the atomic ratio C:H:N:O and express it as the lowest reasonable integer ratio.

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7.
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11.
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15.
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16.
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17.
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20.
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1-How many grams of NaCl would be needed to prepare 150.00 L of a 1.402 M NaCl solution?

............................................................................................................................................................................

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.

............................................................................................................................................................................

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)?


............................................................................................................................................................................

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.

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