Exp 2_1.docx

LABORATORY 2 Partial Molal Volumes Aim To demonstrate the theory of partial molal volumes. The partial molal volume of NaCl will also be calculated. Introduction When dissolving x mol of NaCl in y mol of water, the solution volume is not equal to the molar volume of NaCl plus the molar volume of water. To determine whether a partial molal volumes exist, the theory is tested in a laboratory setting to show the outcome of this experiment. Materials and Methods Observations Peripheral conditions: Room temperature: 24C Time of experiment: 0830Hrs Date of experiment: 13/03/19 Materials To complete this experiment the user will need a flask and pycnometer to measure water in and be able to weigh it. Also a water bath is required with a set temperature of 25C. Standard laboratory items required to complete this experiment such as analytical scales, measuring spoons and parafilm are needed. The two samples required are NaCl and distilled water. Methods This experiment is not complex and can be completed with ease, but much care must be taken to ensure no excess water is not carried onto measuring the weight of the items. Flasks are to be wiped down and clean when measuring. Measure the pycnometer to get the mass of it empty, then fill it with distilled water and place parafilm ontop of it and place it in the water bath to take it to 25C which can take 10-15minutes. Once the time has elapsed weigh the pycnometers and record the mass. Weight a separate empty flask then add 1g of NaCl into it and record the mass again. Now fill it with 50mL of distiller water and record its weight. Pour out the water from the pycnometer and fill it with the NaCl solution and put it into the water bath to set at 25C. Allow 10-15mins for the temperature to arrive at an equilibrium. Remove the pycnometer and weigh the new mass. Repeat for 2g, 4g, 6g, and 8g of NaCl to get more accurate results. Results Results of the experiment will show in figure 1,  vsm. Here we can see there is a relationship between apparent molal volume and the molality. As the molality increases, so does the partial molal volume. The R squared value of figure 1 shows about 20% 1|Page Greg Blasiak 30879042

accuracy, this is due to an outlier in the results giving an Apparent Molal Volume of 37.57 mL/mol. Table 2 is a summary of the calculations and equations used to reach the values required to graph figure 1. The Values of V1 (solvent) and V2 (solute) can be found in table 2.

Conclusions From the raw data captured, it is evident that the total volume changes when adding a set volume of salt to a set volume of water, not by Amagat’s law, the law of addition, but by determining partial molal volumes as the partial volumes of solute and solvent change in solution and give rise to a new total volume.

References Welborne, K. (2015). Partial Molar Volume. [online] prezi.com. Available at: https://prezi.com/mem8t4xuazzr/partial-molar-volume/ [Accessed 28 Mar. 2019].

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Table 1 – Pycnometer volumes

Pycnometer Volumes A empty B+ B-A/P Density of pure (mass) H2O(mass) (volume) water g g cm3 g/cm3 18.5295 28.4963 9.93789628 0.997 18.6418 28.3388 9.6688787 0.997 18.9123 28.8793 9.9380957 0.997 14.2456 23.9398 9.66608682 0.997 18.0791 27.7597 9.65252626 0.997

1 2 3 4 5

Table 2 – NaCl solution weights NaCl %w/w 2 4 8 12 16

NaCl solution weights 50mL flask dry + NaCl + H2O + NaCl H2O g g g g 29.5395 30.3785 80.1267 28.8385 30.3469 79.4705 30.9556 34.7774 83.7253 38.439 43.9394 92.0815 36.6537 44.1747 91.4262

49.7482 49.1236 48.9479 48.1421 47.2515

Table 3 – Pycnometer NaCl solutions

NaCl %w/w 2 4 8 12 16

Pycnometer NaCl solution weights Pycnometer Pycnometer volume +solution mL g 9.9668 28.609 9.694 28.5387 10.2375 29.3915 9.6942 24.6661 9.6806 28.6567

solution g 10.0795 9.8969 10.4792 10.4205 10.5776

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Table 4 – Moles and Molality molality of mol NaCl solution =g(NaCl)/M(58.44) =n(NaCl)/kg(H2O) 0.014356605 0.288585417 0.025811088 0.52543153 0.065396988 1.336052994 0.094120465 1.955055252 0.128696099 2.723640489

mol H2O =g(H2O)*M(18.02) 2.760721 2.72606 2.71631 2.671593 2.62217

Table 5 – Apparent Molal Volume Density. Pycnometer vol/weight of solution

g/mL 1.011307541 1.020930472 1.02360928 1.074921087 1.092659546

Apparent Molal Volume (phi) (1/density soln)*(58.44(1000/molality soln)*((density soln-density solvent)/densit V2=phi + solvent)) Sqrt(m) d(phi)/d(sqrt(m)) m*(d(phi)/d(sqrt(m)) ml/mol Slope on fig1 mL/mol 8.615216606 0.537201468 11.767 9.85967 12.49697155 0.72486656 11.767 15.12894 37.57657978 1.155877586 11.767 46.02772 17.1769489 1.398232903 11.767 30.77838 21.243922 1.650345567 11.767 41.82997

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V1=V1om^2/55.51 * d(phi)/dm mL/mol 17.99353 17.97509 17.79659 17.52096 16.98993

Figure 1 – Apparent Molal Volume vs √Molality NaCl Solution: Apparent Molal Volume vs SquareRoot Molality

y = 11.767x + 6.5574 R² = 0.2347

Molal Volume (mL/mol)

40 phi vs sqrt m

35 30 25 20 15

10 5 0 0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

√m

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Figure 2 – Apparent Molal Volume vs Density NaCl Solution: Apparent Molal Volume vs Experimental density of Solution

40

Molal Volume (mlL/mol)

35 30 25 20 15 10 5 0 1

1.01

1.02

1.03

1.04

1.05

1.06

1.07

1.08

1.09

1.1

Density (g/mL) Series2

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Figure 3 – Calculations and workings for 2%w/w NaCl

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