Dissolving

After working with mixtures, we next investigated Solutions and Dissolving.  We experimented to discover some of the factors that influence the rate of dissolving.  The students learned what a solution, solute, and solvent were.

Dissolving

1. Problem: What are some of the factors that affect dissolving?
2. Hypothesis:
3. Experiment:
A. Materials
For groups of 3 students
1 beaker of salt
1 beaker of rock salt
1 piece of graph paper
4 – 250ml beakers
2 metal stirrers
stopwatch
Balance scale

B. Procedures:
Activity #1
1. Pour 200ml of tap water into 2 beakers
2. Mass 3 g. of salt and place on one half of the graph paper.
3. Mass 3g. Of rock salt and place on the other half of the graph paper.
4. Which particles have a greater surface area?
5. Put the 3 g. of salt and rock salt into 2 different beakers of water and immediately start timing. Stir both solutions.
6. Record the time for how long it took for each to dissolve and any other observations.

Activity #2
1. Empty and rinse out the 2 beakers and refill them with 200ml of cold tap water.
2. Add 3 spoonfuls of salt to one of the beakers and let it sit.
3. Add 3 spoonfuls of salt to the other beaker and stir it for 1 minute and then stop stirring.
4. Record your observations.
5. Empty and rinse out both beakers.

Activity #3
1. Pour 200ml of ice water into 1 beaker
2. Pout 200 ml of hot water into the other beaker.
3. Put 3 spoonfuls of salt into each of the 2 beakers. Do not stir!
4. Record your observations. Which one seemed to dissolve more?
5. Next, stir the contents of each beaker for 1 minute.
6. Record what you observe.
7. Empty and rinse out each beaker.
8. Clean up your work area.
6. Observations:


Qualitative observations: What you have written so far will serve as your observations. However, feel free to add any other observations you made of the 3 activities.

Quantitative observations: I want you do a sketch, or series of sketches, showing what we did and what occurred. Be neat, use labels, motion marks, arrows, etc., and use color.

6. Conclusion: Answer the following questions and questions A, B, C, and D on your Scientific Method Guidelines sheet.

1. Which particles seem to dissolve faster – smaller or larger ones?
2. Which particles have a greater total surface area – smaller or larger ones?
3. How does stirring, or shaking, affect dissolving?
4. How does temperature affect dissolving?
5. A soup recipe calls for bouillon powder or bouillon cubes. Use of which ingredient would speed up the making of the soup?
6. What are three factors that affect dissolving?
7. In a salt and water solution, which one is the solvent and which one is the solute?