Solubility Mini-Lab Presentation

Agnibho, Sara, Pranjal, Monica, Camille, Nick

Essential Question - Station Six

What effect does surface area of the solute have on the rate of dissolution of a solid in a liquid? Answer in terms of molecular motion.


Important Factors to Keep in Mind:

  • What variables exist in your lab?

  • What variable are you manipulating?

  • What are you comparing your results against?

  • How can you verify that your results are valid?

Materials

  • 2 Sugar Cubes
  • Mortar and pestle
  • Stopwatch
  • 2 200mL Glass Beakers
  • 400 mL of Room Temperature Water
  • Pen and Paper to Record Data

Procedure

  1. Carefully crush one 1cm x 1cm sugar cube with pestle in the mortar by pressing down gently.

  2. Continue crushing until the sugar cube reaches a uniform fine powder or grain-like state.

  3. Fill up a 200mL glass beaker with 200mL of room temperature water.

  4. Gently pour the powdered sugar from the mortar into the glass beaker.

  5. Start a stopwatch as soon as all the powdered sugar submerges into the water.

  6. Using a glass stirring rod, stir at a moderate pace (approximately 2-3 rotations per second) for the first 30 seconds.

  7. Stop stirring for 15 seconds and remove the stirring rod from the mixture.

  8. Resume stirring at the 45 second mark.

  9. Attentively observe the mixture and continue stirring the mixture until sugar (the solute) is completely dissolved into the solvent.

  10. Stop the stopwatch when the sugar is completely dissolved into the solvent.

  11. Record the rate of dissolution of the crushed sugar in water.

  12. Fill up another 200 mL glass beaker with 200mL of room temperature water.

  13. Gently place one 1cm x 1cm sugar cube into the beaker.

  14. Start a stopwatch as soon as the sugar cube is completely submerged into the water.

  15. Using a glass stirring rod, stir at the same moderate pace as did for the crushed sugar for the first 30 seconds.

  16. Pause stirring for 15 seconds and remove the stirring rod from the mixture.

  17. Resume stirring at the 45 second mark and continue stirring until sugar cube is completely dissolved. Observe the mixture carefully while stirring.

  18. Stop the stopwatch when the sugar cube is completely dissolved into the water.

  19. Record the rate of dissolution of the sugar cube in water.

Pictures of Experimentation in Process

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Data

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Conclusion

In this lab, the experimental group was assigned to dissolve various forms of sugar cubes as the solute into the solvent water in order to analyze the effects of changing the on the rate of dissolution of a solid. Consequently, it was concluded that increase in the exposed surface area of a solid allows for the solid to dissolve much faster in a liquid solvent than a solid with a less exposed surface area.


During experimentation, the group devised two variations of the sugar cube: one in its full cubicle form and one completely crushed into small granules. Then, the time taken for each to completely dissolve was recorded after moderately stirring with a fifteen second break. As seen by the data tables, the average time taken to dissolve the crushed sugar was 46.5 seconds compared to 59.5 seconds for the uncrushed sugar cube.


The reason for these results can be explained at the molecular level. In a cube-shaped sugar cube, there is not much water that makes direct contact with the individual sugar molecules due to other layers of sugar molecules covering it. Thus, the water first makes contact with the outer sugar molecules and slowly makes its way to the inside to reach the covered molecules. However, in a crushed sugar cube, the water is able to make contact with and surround every sugar molecule almost instantly after it is dropped into the water solvent. This way, the dissolution rate quickens as there is no time delay of the water having to wait for one sugar molecule to dissolve in order to reach the others. As seen, the data reflects this reasoning as it took approximately 13 more seconds for the cube-shaped sugar block to dissolve than it did for the crushed sugar block.


Overall, the experiment was successful and it allowed the experimental group to better understand the effects of the surface area of a solid solute on its dissolution rate in a solvent.

Error Analysis

There were evident faults in the process of experimentation that could have contributed to the inaccuracy of the data. One such fault was the inconsistent temperature of the water. The temperature of the water was not measured while dissolving the sugar. If there was an increase in temperature of the water, the sugar would dissolve faster and vice versa. As a result, it is not possible to be sure if the dissolution rate was due to the increased surface area or due to a change in temperature.


Also, pressure, causes the solute to be increased in the solvent, because the pressure forces the remaining gases into the solute. Therefore, pressure increases the solubility, and also changes the reaction rate. Since it is not possible to tell if the pressure remained the same throughout the entire lab, it could be a possible error that resulted in inaccurate data.


Additionally, in the lab, the solution containing the water and the sugar was occasionally stirred in order for the sugar to dissolves into the water. This might have resulted in an increase in temperature and thus caused a change in data.


Furthermore, the incomplete crushing of the sugar cube when testing for the rate of dissolution for the increased surface area of the sugar cube would result in a slower rate of dissolution. Increasing the surface area of a solute would increase how quickly the solute dissolves in a solution. If the sugar cube was broken down more than the surface area of the crushed sugar cube would be much greater than if weren’t broken down as much and it would have greater contact with the water molecules. These errors definitely did contribute to some deviations in data, but they will be kept in mind if this lab were to be conducted again sometime in the future.