Chemistry Portion

Research Question

How effective is a sand filtration system in filtering baking soda, NaHCO₃(s), from a 0.5M baking soda solution, NaHCO₃(aq)?

Hypothesis

The HCO₃^- ions are the conjugate bases of a weak acid, while Na⁺ is a strong cation which does not affect its pH. When some of the NaHCO₃ dissociates, the basic HCO₃^- ions will increase the pH. Filtering a baking soda solution, NaHCO₃(aq), through a sand filtration system will decrease the concentration of baking soda solution, and thus be an effective filtration system. 

Apparatus

Chemicals	Glassware	Measuring Tools	Miscellaneous
ü 82 g NaHCO3(s) ü Distilled/Deionized Water	ü  1 L Volumetric Flask ü  Multiple 100 mL and 500 mL beakers for transferring ü  Distillation apparatus ü  100 mL Graduated Cylinder	ü pH probe ü Analytic scale	ü Magnetic Stir Bar ü Hot Plate with Magnetic Stirring Function ü Paper filters

 Distillation Apparatus

("Rhodium Distillation Apparatus")

 Obligatory photo of Arber smiling next to the distillation apparatus prior to transferring the NaHCO₃(aq) solution to the round-bottom flask.

Top-down view of distillation apparatus set up with the solution of NaHCO₃(aq) after going through the filter

Juan explaining the distillation process

Data and Procedures

Procedures before filtration

1. Mass 42.00 g NaHCO₃(s) and add it to a 1 L volumetric flask.

2. Add water to the volumetric flask containing the NaHCO₃(s). Fill to the mark for 1 L.

3. Drop a magnetic stir bar in the volumetric flask and use a magnetic plate to mix the solution until the NaHCO₃(s) completely dissolves. Heat the solution at the lowest setting of the hot plate, while leaving the cap off. Adjust the heating capability as needed.

4. Remove the magnetic stir bar and quantitatively transfer the 500 mL of the NaHCO₃ solution to a 500mL beaker, while transferring the rest to another. One of these solutions will be used for Trial 1, while the other will correspond to Trial 2.

5. Using a pH probe, record the initial pH of both NaHCO₃(aq) solutions.

6. Set a 500mL beaker at the output end of the filter. Pour the solution of Trial 1 through the sand filter and collect the yield with the beaker. Stir the solution with the stirring rod and measure the pH after filtering.

7. Quantitatively transfer the NaHCO₃(aq) to a 100 mL graduated cylinder and record the volume. It will probably be over 100 mL, so this may be done multiple times by transferring some of the solution to another 500 mL beaker.

8. Set up the distillation apparatus and quantitatively transfer the NaHCO₃(aq) solution to the round-bottom flask. Heat the solution until it begins to boil.

10. Monitor the solution closely and turn off the heat source once the solution stops boiling. Record the volume of distilled water collected.

11. Measure 75.0 mL of distilled water with the 100-mL graduated cylinder and add them to the round-bottom flask once it has cooled to collect the sand and NaHCO₃(s).

12. Set up a system of vacuum filtration using a Büchner funnel. Filter the solution twice through with paper filters, and collect the resulting solution with a 100-mL beaker. Record the volume of the collected NaHCO₃(aq).

13. At this point, some of the volume will be taken for testing for the Biology portion. Measure the volume of some of the collected NaHCO₃(aq) solution with a 100-mL graduated cylinder and mass the solution with an analytic scale. Subtract the first value from the last to give the mass of NaHCO₃(s) dissolved in the distilled water.

Experimental procedures and data after filtration

0.50 M Solutions of NaHCO₃

	Trial 1	Trial 2
Initial Mass of NaHCO3	42.032 g	42.039 g
Initial solution pH	10.36	9.98
Initial volume	500 mL	500 mL
Volume after filtration	310 mL

       

Juan exemplifying his pride in mixing a 0.5M solution of NaHCO₃

   Only the Trial 1 solution from was filtered. Initially, the resulting solution was covered in sand and gravel, but as the filtering process progressed, the amount of sand and gravel decreased. The initial “muddy” output of the filter was collected separately from the clearer solution that came forth later. Their pH values were measured separately as different solutions, before being mixed together again.

	Muddy Solution	Clear Solution	Mixed Solution
pH	9.15	9.42	9.40

Arber astounded by the opacity of different portions of the solution after filtered.

"Muddy" solution in right hand, "Clear" in left hand.

The pH values stay relatively close, suggesting that the sand and gravel only make the solution slightly more acidic since when they’re mixed, the pH equalizes to 9.40. Finally, after being distilled with a distillation apparatus, the volume of the water filtered was found.

Volume after filtration	310 mL
Volume of distilled water	188 mL
Volume of NaHCO3, sand, gravel,  etc.	122 mL

Afterwards, 75 mL of distilled water was added to the sand and filter in the round-bottom flask to remove most of it.  The resulting solution was vacuum filtered twice with a Büchner funnel. Filter paper was used in the filter to prevent sand from remaining in the solution, while suction was added to create a vacuum with the water. When the filtering was done, the solution was much clearer than before, with only traces of sand. Only 71.0 mL remained.

To measure the mass of the remaining NaHCO₃, 32.5 mL (approximately half) of the solution was massed with an analytic scale. The volume was subtracted from the resulting mass (assuming the density of distilled water to be 1.0 g mL^-1), and the result was the mass of the NaHCO₃ that remained after both filtration processes. Although obviously, some sand remained, we will assume this to be negligible for the purpose of simplicity.  Turning this value back into moles (by dividing by the molar mass of NaHCO₃) and dividing this value by 32.5 mL gives an approximation of the molarity.

Volume of distilled water added to the round-bottom flask	75.0 mL
Volume of solution after filtration	71.0 mL
Volume of solution massed	32.5 mL
Total mass of the 32.5 mL solution	34.004 g
Mass of NaHCO3 recovered in the 32.5 mL solution	1.5 g
Moles of NaHCO3 recovered in the 32.5 mL solution	0.018 mol
Molarity of the 32.5 mL solution	0.51 M

Conclusion and Evaluation

According to our data, the molarity of the NaHCO₃ solution did not actually decrease as a result of the filtering processes. Instead, our data shows that it increased, although this is because of the sand that was inadvertently added to the solution. It seems that the molecules of NaHCO₃ were small enough to pass through the filter along with the water. Perhaps it was because only 32.5 mL of the solution were used to verify the molarity; if a higher volume of the solution was used, there would be a more precise measurement of the molarity. A markéd difference was noted in the pH of the solution, however. The pH of the solution decreased from 10.36 to 9.40. This difference explains that although the filter did not necessarily filter any of the NaHCO₃ solution, it did make the solution more acidic, and thus, more neutral.