Exp 12 results only Bailey Dabney PDF

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Mol a rMas sofaVo l a t i l eLi qui d Ba i l e yDa b ne y La bPa r t n e r :Ta l e x iGa s a l CHEM 13 0 0La b ,EV3 Li s aBa p t i s t e Ne e t h uMa t h e w 2 3Oc t o b e r2 0 18

Da t a Data Table: Experiment 12 Report Sheet Unknown: Barcelona Preparing the Sample Mass Of Dry Flask, Foil And Rubber Band

Trial 1 86.89 g

Trial 2 87.39 g

Trial 3 87.94

Trial 1 90 ℃ 87.20 g

Trial 2 90 ℃ 87.71 g

Trial 3 90 ℃ 88.04 g

Trial 1

Trial 2 143 mL = 0.143 L 763.3 torr

Trial 3

Trial 1

Trial 2 3.66 mol 0.32 g 0.087 g/mol 0.066 g/mol 1.143 x 10-3

Trial 3

Vaporize The Sample Temperature Of Boiling Water Mass Of Dry Flask, Foil, Rubber Band And Vapor (G) Determine the Volume and Pressure of the Vapor Volume Of 125- Ml Flask (L) Atmospheric Pressure (Torr, Atm)

Moles Of Vapor Mass Of Vapor Molar Mass Of Compound Average Molar Mass Standard Deviation Of Molar Mass

0.31 g 0.084 g/mol

Relative Standard Deviation Of Molar Mass

0.1 g 0.027 g/mol

1.73%

Ca l c ul a t i o ns( Tr i a l1 ) : 1. Moles of Vapor: a. Nvapor =

PV RT

=

(763.3 atm )(143 L) atm (0.08206 L∙ ∙ K )(363.15 K) mol

2. Mass of Vapor: a. mvapor = mflask + vapor - mflask b. mvapor = (87.20) – (86.89) c. mvapor = 0.31 g 3. Molar Mass of Compound:

= 3662.8 mol = 3.66 mol

a. Mcompound =

m vapor n vapor

=

0.31 g 3.66 mol

= 0.084 g/mol

4. Average Molar Mass: a.

(Trial 1 molar mass)+(Trial 2 molar mass)+(Trial 3 molar mass) 3

b.

(0.084 g /mol)+(0.087 g/ mol)+(0.027 g / mol) =0.066 3

5. Standard Deviation Of Molar Mass:

a.

b. c.

0.066 0.084−¿ ¿ 0.066 0.087−¿ ¿ 0.066 0.027−¿ ¿ ¿2 ¿ ¿ √¿

√ √

(0.018)2+(0.021 )2+(−0.039 )2 2 2.286 x 10−3 2

d. 1.143 x 10-3 6. Relative Standard Deviation Of Molar Mass: a. RSD =

Standard Deviation Average Molar Mass

b. RSD =

1.143 x 10 0.066 g/mol

−3

c. RSD = (0.0173) x 100 d. RSD = 1.73%

Di s c us s i on

x 100

x 100

g/mol

In this experiment, we looked at the molar mass of several components. We look at the mass of the flask, mass of the vapor and the mass of the unknown compound. A number of analytical methods can be used to measure the molar mass of a compound; of course, these options depends of the properties of the compound. To find the molar mass of larger molecule use an osmometer while smaller molecules use its own melting point change to determine the molar mass. In the case of our experiment and the use of volatile liquids, the find the molar mass, the Dumas method is used to produce an accurate determination of molar mass. In this procedure, the liquid is vaporized into a fixed- volume vessel (flask) at a prearranged temperature and barometric pressure. In our experiment, we prepared our flasks and placed about 5 mL of the unknown liquid, Barcelona and covered the opening with aluminum foil. We secured the aluminum foil with rubber band and pierced the aluminum foil several time to allow the sample’s vapor to escape. After the sample was prepared, we filled a 400 mL beaker with water and heated it 90 ℃ , which is hot enough for the water to reach a gentle boil. Once the water reaches a gentle boil, we lowered a flask into the bath and secured it with a utility clamp. We allowed the sample in the bath for several minutes, until we noticed the vapors escaping from the holes in the aluminum foil were no longer present. We continued heating for an additional five minutes and we recorded the temperature of the boiling water. After we measured the temperature of the water, we removed the flask and allowed it to cool to room temperature and determined the mass of the flask, aluminum foil and rubber which resulted in a mass of 86.89 g for the first trail. The flask, aluminum foil, rubber and sample resulted in a mass of 87.20 g. The next step in our experiment was to determine the volume pressure of the vapor and this was done by first, measuring the volume of the flask used. The volume of the flask was 143

mL. We needed 143 mL in liters so we converted it to L, which was .143 L. The atmospheric pressure was given by the instructor which was 763.3 torr. Having these measurements, we are able to calculate the final portion of our experiment. These measurements were used to determine the mole of the vapor, the mass of the vapor, the molar mass of the resulted compound, the average molar mass, the standard deviation of the molar mass and finally, the relative standard deviation of the molar mass. To determine the moles of the vapor, we use the ideal gas law equation which is pressure times volume divided by the universal gas constant and the temperature, in Kelvin. When we plugged in these measurements into the equation, we get that the moles of the vapor were 3.66 mol. Having determined the moles of the vapor, we were able to determine the mass of the vapor. To figure out the mass of the vapor, we subtract the mass of the flask and sample minus the initial flask which resulted in 0.31 g. Following this, we determine the molar mass of the compound and this was determined by dividing the mass of the vapor by the moles of the vapor which resulted in 0084 g/mol. With the molar mass of the compound and the measurements from trial 2 and trial 3, this allowed us to determine the average molar mass, which is done by adding the molar mass of all three trials and dividing by 3, due to the number of trials. The average molar mass resulted in 0.66 g/mol. Finally, the last two calculation wrap up this experiment and it deals with determining the standard deviation and the relative standard deviation of the molar mass. To determine the standard deviation, we took the molar mass minus the average molar mass and squared that, and this was done for trial 2 and 3. Once we have that, we divided all this by 2 and resulted in 1.143 x 10-3 and the relative standard deviation of the molar mass was 1.73%. This was calculated by dividing the standard deviation by the average molar mass. Co nc l us i o n

As we can see, the purpose of this experiment dealt with molar mass and the measure the physical properties of pressure, volume and temperature for a gaseous substance. Throughout this experiment, we were able to determine the moles of the vapor, mass of the vapor and average molar mass. Our hypothesis was that we were going to successfully measure the mass and moles of the vapor, which we did. Po s tLa bQue s t i o ns 3. A. Suppose the thermometer is miscalibrated to read 0.3°C higher than actual. Does this error in calibration result in the molar mass of the vapor in the flask being reported as too high, too low, or as unaffected? Explain a. This error in calibration can result in the molar mass of the vapor in the flask to be too high because it would speed up the evaporation process of the sample. 3. B. If the volume of the flask is assumed to be 125 mL instead of the measured volume, would the calculated molar mass of the unknown liquid be too high, too low, or unaffected by this experimental error? Explain. a. In my opinion, the calculated molar mass of the unknown liquid would be considered too low because the volume would “wash” out the sample. 4. The pressure reading from the barometer is recorded higher than it actually is. How does this affect the reported molar mass of the liquid: too high, too low, or unaffected? Explain. a. I do not think the reported molar mass of the liquid would go unaffected.

Re f e r e nc e

Be r a n, J .A." Pe r c e ntWa t e ri naHyd r a t e dSa l t . "La b or a t o r yMa n u alFo rPr i n c i p l e so f Ge ne r a lCh e mi s t r y . 10 t he d . N. p. :n. p . , 2 0 07 . 8 5 9 0 . Pr i n t ....