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Solutes and Solubility

Deep Analysis

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Deep Analysis

Solutes and Solubility

Deep Analysis

Use the questions below to go deeper into the scientific concepts and applications of each Investigation. Note that questions highlighted in orange text are also featured in Phase 3.1 (Conclusions) of the Student Guide PDF.

Investigation 1

      When students have finished their Investigation, use the board to combine the data from each student group and ask students to complete Table C.

      Discuss the solubility of each of the compounds in water.

      • Did all masses of each compound dissolve? No, some larger masses of the compounds did not dissolve.
      • Was the mass of each compound that did not dissolve the same or different? The masses for each compound were different.

      Instruct students to complete the Analysis Questions in their SDRs then discuss them as a class. Use the suggested responses below to guide students’ answers.

      • What was the highest concentration at which baking soda (NaHCO3) was soluble in water? 5 g baking soda per 100 ml water
      • What was the highest concentration at which salt (NaCl) was soluble in water? 10 g salt per 100 ml water
      • What was the highest concentration at which sugar (C12H22O11) was soluble in water? 50 g sugar per 100 ml water
      • Between what masses is the saturation point of each of the compounds?
        • baking soda: 5 – 10 g per 100 ml water
        • salt: 10 – 50 g per 100 ml water
        • sugar: 50 – 100 g per 100 ml water
      • Does a solute have a maximum concentration in a certain volume of water? Why or why not? Yes. For each solute, there was an amount of sample that would not dissolve in 100 ml of water. For example 0.3 g, 1.5 g, and 5 g of baking soda dissolved in 100 ml of water, but 10g did not. The maximum concentration of solute that will dissolve in a certain amount of water is the solute’s saturation point. A solute reaches a saturation point because the solvent particles are not able to surround each solute particle.
      • Did the different solutes have the same solubility or a different solubility? Each different solute had a different solubility. No more than 5 g of baking soda, 10 g of salt, and 10 g of sugar dissolved in 100 ml of water.
      • Look at the chemical formulas for the compounds tested in the experiment. Do compounds composed of the same elements have the same solubility or a different solubility? Compounds composed of the same elements have different solubilities.

      Investigation 2

          • Calculate: What was the rate of solubility for each compound when not stirred? Use the class data to complete Table E.

          • Calculate: What was the rate of solubility for each compound when stirred? Use the class data to complete Table F.

           

          • Did stirring increase the rate of solubility of each of the compounds? Use data from the experiment to support your answer. Stirring increased the rate of solubility of all of the compounds. When not stirred, none of the three compounds dissolved in less than 6 minutes. All of the compounds dissolved between 2 and 5 minutes when stirred.
          • Why did stirring increase the rate of solubility of the compounds? Student answers will vary. Stirring increased the rate of solubility by dispersing the particles of solute more evenly so the particles of solvent could more easily surround the solute particles.
          • Look at the data in Table F. Compare the chemical formulas of the compounds tested. Does stirring increase the solubility and rate of solubility of compounds made of similar elements? Stirring increased the rate and solubility of all the compounds composed of the same element. Stirring always increased the rate of solubility.
          • Look at the data in Table F. Compare the chemical formulas of the compounds tested. Does stirring increase the solubility and rate of solubility of compounds made of different elements? Stirring increased the rate and solubility of all the compounds composed of the different elements. Stirring always increased the rate of solubility.
          • Look at the data in Table F. Compare the chemical formulas of the compounds tested. Do the elements that make up the compound affect its rate of solubility? Each compound has a different formula and has a different rate of solubility suggesting that the differences in the chemical formulas affect the rate of solubility.
          • Make a prediction. Are there any other ways to change the rate of solubility of a solute? Student answers will vary.

          Investigation 3

            • Combine your data with the data from the other groups by completing Table E.

            • Did each of the compounds dissolve in cold water? None of the compounds dissolved in cold water.

            • Did each of the compounds dissolve in hot water? All of the compounds dissolved in hot water.
            • How does temperature affect the solubility of solutes? Use data from the experiment to support your answer. Increased water temperature increases the solubility of solutes. The temperature of the hot water was 45°C compared to cold water which was 6°C. None of the compounds dissolved in cold water in 6 minutes. All of the compounds dissolved in the hot water in 1 or 2 minutes. More of each compound dissolved in hot water as compared to cold water.
            • Calculate: What was the rate of solubility for each compound in cold water? Use the class data to complete Table F.

            • Calculate: What was the rate of solubility for each compound in hot water? Use the class data to complete Table G.

            • How does temperature affect the rate of solubility of solutes? Use data from Tables F and G to support your answer. A greater amount of each solute dissolved in a shorter amount of time in the hot water as compared to the cold water. Increasing the temperature increased the rate of solubility of all of the compounds.
            • Why did using hot water increase the solubility and rate of solubility of the solutes? Hot water increased both the solubility and the rate of solubility by causing the particles of solute to move more quickly so the particles of solvent could more easily surround the solute particles.
            • Compare the chemical formulas of the three compounds in Tables F and G. Does increasing the temperature of the solvent increase the solubility and rate of solubility of compounds made of the same elements? Increasing the temperature increased the rate of solubility of all the compounds. Compounds composed of similar elements all experienced an increase in solubility and rate of solubility as the temperature of the solvent increased.
            • Compare the chemical formulas of the three compounds in Tables F and G. Does increasing the temperature of the solvent increase the solubility and rate of solubility of compounds made of different elements? Increasing the temperature increased the rate of solubility of all the compounds even though each compound was composed of some elements that were different.