Chemistry

Temperature and Dissolution



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Research

The temperature of an object can essentially be described as the sensation of warmth or coldness felt with contact. However, this is only on a physical scale, as temperature is truly the measure of energy of thermal molecular motion. Once temperature reaches an absolute zero, energy is reduced to minimum amount (Lynds, 1995). This basically signifies that the temperature of an object has a direct relation to the energy of that object.
When a solid substance, a solute, dissolves into a liquid substance, a solvent, they react to form an intimate mixture called a solution. This process of dissolution will not occur if the particles of both substances are unable to bond together (Jones, 2000). As with any reaction, dissolution requires energy, known as activation energy, to break and reconnect bonds (Morgan, 1995).
As stated earlier, the temperature of a substance will directly affect the energy within the substance's molecules. As a result, a solvent at a higher temperature should have more molecular energy during the dissolution process, making it easier to break and reconnect particles to form a solution. However when a liquid is cooled, the average energy of molecules decrease and particles slow down, making the dissolution process more difficult ("Effects of Temperature and Pressure", 2007). A perfect example of this is when liquid water compounds reach a temperature so low that they freeze into a solid form, known as ice. The molecules inside of the water compounds actually freeze themselves because of the low temperature and lack of energy to form the new state of matter (Carpi, 2003).

Problem: What is the effect of temperature on the dissolution speed of a substance?

Purpose: Most solid chemicals have to be dissolved in water or other solvents before they can be used. By knowing the most efficient temperature for dissolving certain chemicals, scientists can save time and energy in the dissolution process.

Hypothesis: The student believes that higher temperatures will cause substances to dissolve faster, since higher temperature means higher molecular motion and energy according to the research.

Independent Variable: Temperature of water solvent (measured in degrees Celsius)

Dependent Variable: How long it takes for the solute substance to dissolve in the water solvent (measured in seconds)

Constants: Amount used of each substance (2ml), materials used, amount of water used as a solvent (200 ml)

Materials:

Water
Measuring Cup
Clear Plastic Cups
Sugar
Salt
Baking Powder
Flour
Thermometer
Stopwatch

Procedure (For 1 Trial):

1)Run water from facet into measuring cup up to desired amount
2)Measure temperature of water with thermometer
3)Put water into a cup
4)Pour substance into measuring cup up to desired amount.
5)Place substance into cup with water
6)Watch as substance dissolves and use stopwatch to measure the time

Results:

Trial 1
Temperature Time to Dissolve
Salt 43.33C 65.57s
Sugar 48.89C 49.96s
Flour 44.44C 97.9s
Baking Powder 44.44C 73.3s

Trial 2

Temperature Time to Dissolve
Salt 63.33C 15.73s
Sugar 73.89C 40.04s
Flour 65.56C 74.05s
Baking Powder 58.89C 69.76s

Trial 3

Temperature Time to Dissolve
Salt 82.22C 14.61s
Sugar 83.33C 25.87s
Flour 85C 23.71s
Baking Powder 83.33C 41.23s

Conclusion

All the substances dissolved faster in water at higher temperatures, thus accepting the student's hypothesis. This also concludes that temperature directly affects dissolution rate; meaning that as temperature increases, so will the rate at which the solvent dissolves a solute substance.
A potential way to improve the project would be to have different set temperatures used as the independent variable, instead of miscellaneous temperatures for every individual measurement. A possible error could have been the exact timing of the dissolution, because it could not always be absolutely obvious as to when the substance was completely dissolved.
The results of this experiment have good value as they accurately depict the effect of temperature on the speed of dissolution not only with one substance, however with several substances.

Literature Cited

"Effects of Temperature and Pressure".November 2007.

Atkins, P.W.Molecules.1987.November 2007

Carpi, Anthony."Water Properties and Behavior".2003.
Visionlearning.November 2007.

Jones, R."Dissolving".Particle Theory.November 2000.SCIcentre.November 2007.

Lynds, Beverly."About Temperature".Project Skymath.November 1995.November 2007.

Morgan, Nina.Chemistry in Action: Molecules in Everyday Life.1995.November 2007

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