Planning and Designing Chemistry Lab – Determining the solubility of salt at different temperatures.

Planning and Designing Chemistry Lab – Determining the solubility of salt at different temperatures. 

Problem:

You are given a salt and asked if the salt will dissolve in water more at high temperatures.

Hypothesis:

The salt will dissolve more at room temperature.

Aim:

To determine the solubility of a salt at different temperatures.

Apparatus:

salt, distilled water, tripod stand and gauze, Bunsen burner, beakers, ice, filter paper, funnel, thermometer, watch glass and stop-watch

Method:

  1. Weigh out four equal amounts of the salt and place in four (4) separate test-tubes.
  2. Measure out four 25cm3 of distilled water and place in four beakers.
  3. Prepare the water to the following temperatures – 0°C, 30°C, 60 °C and 90°C
  4. Prepare a bath-water and heat the water to 60°C and to a boil to 90°C
  5. Place the salt in each container of water and stir for 20 seconds.
  6. Immediately pour the solution through a filter paper.
  7. Allow the residue to dry and reweigh.
  8. The one with the highest mass was most in-soluble.
  9. Tabulate Results.

Variables:

Controlled:

  • Volume of water used
  • Amount of salt used
  • Time given for salt to dissolve

Manipulated: Temperature

Responding: Amount of salt that remains undissolved

Expected Results:

Chemistry diagram 13

Treatment of Results:

 

To calculate the solubility of each salt at the different temperature, you will need to use the formula:

Chemistry diagram 14

Interpretation of Results:

The solubility of a given solute in a given solvent typically depends on temperature. For many solids dissolved in liquid water, the solubility increases with temperatures up to 100 °C. As the temperature of a solution increases, the average kinetic energy of the molecules that make up the solution also increases. This increase in kinetic energy allows the solvent molecules to more effectively break apart the solute molecules that are held together by intermolecular attractions.

The increased vibration (kinetic energy) of the molecules causes them to be less able to hold together, and thus they dissolve more readily. Therefore if the solubililty of the final salt in the 30°C water has the highest solubilty then the hypothesis is accurate. If the solubility is higher as the temperature increases then the hypothesis is not accurate.

 

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