Cond:grav of barium sulfate 2 PDF

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CHEMISTRY 113 LAB...

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Cond/grav of barium sulfate. Introduction: The purpose of this lab is to analyze a solution of barium hydroxide of unknown concentration. The concentration of a basic solution can be determined by detecting the equivalence point. The quantitative analysis of Barium hydroxide can be performed in two ways; by conductimetric titration and by gravimetric determination. Conductimetric titration is used to find out the concentration of the given substance. This method involves adding of a reactant to a reaction mixture and monitoring the conductivity of the reaction mixture to determine the equivalence point. Whereas gravimetric determination is a technique through which the amount of the substance can be determined through weighing. In order for gravimetric analysis to be accurate, it must meet five requirements. The compound formed must be pure and of known stoichiometry. The precipitation reaction must be complete. There should be no interference by any other types of compounds forming precipitates. The precipitate must be easily filtered, hence the solid should be in form of large, well formed crystals. Lastly, the weight of the solid should be high enough so a reason weight of precipitate is generated. Procedure: 1. A 10 mL graduated cylinder should be used to transfer 10.0mL of Barium Hydroxide solution into a 100 mL beaker. Add 30 mL of distilled water using the same graduated cylinder in 10 mL increments. (Avoid spilling on skin or clothing as Barium Hydroxide is caustic). 2. Connect the drop counter to DIG/SONIC 1 of the Vernier computer interface and lower it onto the ring stand. 3. Connect the conductivity sensor to channel 1 of the interface. Set the selector switch on the conductivity probe to the 0-20,000 range. Connect the interface to the computer with the proper cable. 4. Start the Logger Pro program on your computer. Open the file “16b Conductivity Titration from the advanced chemistry with vernier folder. 5. Measure 60 mL of 0.100M sulfuric acid into a 250 mL. (Sulfuric acid is a strong acid, so should be handled with care). 6. Obtain a plastic 60 mL reagent reservoir. Close both the valves by turning the handles to a horizontal position. 7. Fill the reagent reservoir with water and test for leaks. The valves should not be leaking, Then empty the water from the reservoir. 8. Rinse the reagent with a few mL of the 0.100M sulfuric acid solution and pour the rinse into an empty 250 mL beaker. 9. Attach the reservoir to a ring stand using a utility clamp. 10. Fill the reagent reservoir with slightly more than 40 mL of 0.100M sulfuric acid.

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11. Place the 250 mL beaker containing the rise sulfuric acid, right below the tip of the reservoir. 12. Turn both valve handles to the vertical position for a couple of seconds to drain a small amount of the sulfuric acid solution into the 250 mL beaker so that it fills the reservoir’s tip. Then turn both the valves back to horizontal. 13. Open the top valve vertically. Slowly open the Botton valve until you have attained a drop rate of about one drop per second. After setting this, do not touch the bottom valve. Close the top to start and stop the liquid flow. 14. Discard the drained sulfuric acid in the 250 mL beaker. 15. Open the experiment menu on top row of the Logger Pro toolbar. Choose calibrate - DIG 1: Drop counter (mL). 16. Select the automatic button. 17. Place a clean and dry 10 mL graduated cylinder directly below the slot on the drop counter, lining it up with the tip of the reagent reservoir. (Make sure the drops fall directly through the middle of the drop counter. 18. Click the start button on the computer. 19. Open the top valve on the reservoir to start the flow. The computer should show the drop count. 20. When the volume of sulfuric acid in the graduated cylinder is between five and 6 mL, close the top valve of the reagent reservoir. 21. Enter the precise volume of sulfuric acid in the graduated cylinder in the edit box. Record the number of drops/mL displayed on the screen. 22. Click OK. Discard the sulfuric acid solution in the graduated cylinder. 23.To assemble the apparatus, insert the conductivity sensor through the large hole in the drop counter. The drops should line up with the center of the magnetic stirrer. 24. Place the magnetic stir bar in the beaker of barium hydroxide solution and lift up the conductivity sensor. Slide the 100 mL beaker containing barium hydroxide onto the magnetic stirrer. 25. The drops must fall through the drop counter in the exact center. 26. Click collect on the computer to begin monitoring conductivity. No data will be collected until the first drop goes through the drop counter slot. Open the top valve fully. 27. Observe the graph. The titration curve should be V shaped. After the conductivity reaches 5000 microsecond, click stop. Close the top valve. 28. Find the equivalence point on the graph, this is the volume when the conductivity value reaches a minimum. Highlight the linear portion where the conductivity is decreasing only. After highlighting click on linear fit button. Do the same for the linear portion where the conducti city is increasing past the equivalence point. Click linear fit button. 29. Highlight the area where these two lines intersect and go to the analyze menu and select interpolate. Drag the cursor to the volume displayed in the equivalence point. Record the readings. 30. Place the beaker with the titrated solution on a hot plate and begin heating till it boils. 31. When the solution forms into small masses, weight the now cool filter crucible, and place it in the vacuum filtration apparatus. 32. Remove the solution from the hot plate once it boils and allow it to cool to room temperature.

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33. Spray about a milliliter of methanol into the crucible to wet the filter disk. Turn the vacuum on. 33. Sir the solution to avoid the barium sulfate turning into solid and begin filtering. Once all the liquid is out of the beaker, rinse any remaining barium sulfate remaining in the beaker into the crucial using methanol.Wash the precipitate with methanol and allow the crucible to sit on the vacuum for about a minute. 34. Place the crucible with the precipitate in the drying oven and dry it for 15-20 minutes. 35.Remove the beaker from drying oven and place in the desicooler to cool. 36. After cooling, record the weight of the crucible with the barium sulfate and then determine the mass of barium sulfate calculated. This will help calculate the original concentration of barium hydroxide. 37. Discard the barium sulfate in the solid waste container. 38. Rinse the conductivity probe tip and solvent reservoir with distilled water and blot dry. Observations and Data collection: Ba(OH) (aq) + H SO (aq) → BaSO (s) + 2 H O (l) 2

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Conductimetric titration data: Initial volume of sulfuric acid

40.00 mL

Equivalence point

10.61 mL

Molarity of sulfuric acid solution

0.100 M

Moles of barium

0.001061 mol

Volume of original barium hydroxide solution

10.00 mL

Concentration of barium hydroxide

1.061 M

Table 1: Conductimentric titration data Gravimetric determination data: Mass of crucible and precipitate

24.610 g

Mass of crucible

24.340 g

Mass of precipitate (barium sulfate)

0.279 g

Concentration of barium hydroxide from gravimeteric

0.120M

Table 1.1: Gravimetric determination data

The table 1.2 below shows any possible human errors that may have occurred.

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Source of error

Effect on experiment

How to minimize the error

Parallax error while measuring barium hydroxide.

Affects the reliability and accuracy of the data.

Look perpendicularly to the measurement apparatus.

Lining the drop counter and the reagent reservoir.

Inaccurate reading of drop counts which leads to inaccurate reading of equivalence point.

Line the drop counter and the reagent reservoir correctly.

Table 1.2: Human error analysis Calculations: Conductimetric titrations: 1. Equivalence point from titration = from the graph when conductivity value reaches minimum. 2. Molarity of sulfuric acid = from the labelled bottle. 3. Moles of barium from titration = equivalence point volume (L) x molarity of sulfuric acid. 4. Concentration of barium hydroxide = moles of barium/volume of barium hydroxide.

Gravimetric determination: 1. Mass of crucible and precipitate = using the analytical balance. 2. Mass of crucible = using the analytical balance. 3. Mass of precipitate (barium sulfate) = mass of crucible and precipitate - mass of crucible. 4. Concentration of barium hydroxide = moles of barium/volume of barium hydroxide.

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Discussion and Conclusion:

Figure 1: Conductimetric titration The graph above shows the conductivity measured using the probe during titration. Using the conductimetric and gravimetric techniques of titration, we were able to find the concentration of barium hydroxide by determining the equivalence point. We found the equivalence value from this graph. The equivalence point is volume when the conductivity value reached its minimum. Using the equivalence point, the concentration of the barium hydroxide was found. The equivalence point in our experiment was 10.61 mL. Using this value, we found the concentration of barium hydroxide which was 1.061M. Concentration of barium hydroxide was found using both conductimetric titration and gravimetric titration. The concentrations of barium hydroxide obtained from both the techniques may not be accurate as there is a difference between the two. There may be errors in the experiment which may not always be human errors. Errors in the conductimetric titration technique could have been because of the drop counter. The red light stopped blinking sometimes and only came back after a few seconds. It may not calculate all the drops. This would lead to inaccurate readings of drop counts which leads to inaccurate reading of equivalence point. To minimize this, align the drop counter and the reagent reservoir correctly. There could be inaccuracy while measuring barium hydroxide and sulfuric acid because the graduated cylinders and beakers could be read wrong. Look at the apparatus perpendicularly. Whereas in the gravimetric determination, errors could have been from the flocculation of the solution. To minimize this, stir the solution quickly and well to prevent any masses from forming. Achieving the perfect boiling point or the room temperature is difficult as well. This could have been another source of error for this technique. Comparing both the techniques, Gravimetric determination may be more accurate because we use analytical balance. This technique does not require as many calculations as conductimetric does. There is less error of measuring instruments as well.

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