The Goal: To isolate pure salt crystals from a salt water solution.
Controls (Things We Keep Constant):
* Type of salt: You'll want to use the same type of salt throughout the experiment (e.g., table salt, rock salt).
* Starting volume of saltwater: Maintaining a consistent amount of saltwater ensures that the results are comparable.
* Heating method: Using the same heat source (e.g., stovetop, hot plate) and temperature setting for evaporation will maintain a consistent rate of evaporation.
Variables:
* Independent Variable: The factor you change to see its effect on the outcome. In this case, the most common independent variable is the method of separation. Here are some examples:
* Evaporation: Boiling the water until it evaporates completely, leaving the salt behind.
* Solar evaporation: Placing the saltwater in a shallow container and allowing the sun to evaporate the water.
* Freezing: Freezing the saltwater, removing the ice (which is mostly pure water), and then melting the remaining ice to get a more concentrated salt solution.
* Dependent Variable: The factor that you measure or observe. In this case, the dependent variable is the amount of salt recovered. You can measure this by weighing the salt crystals after they have been separated.
Additional Considerations:
* Purity of the salt: The purity of the salt recovered depends on the method of separation. Some methods may result in a higher percentage of impurities in the final salt.
* Time: The time it takes to separate the salt will vary depending on the method used.
* Safety: If you are using heat, it's important to be careful and avoid spills or burns.
Example Experiment:
1. Control: Use the same type of salt, starting volume of saltwater, and heating method for each trial.
2. Independent Variable: Test different methods of separation: evaporation, solar evaporation, and freezing.
3. Dependent Variable: Measure the amount of salt recovered from each method.
Conclusion: You can compare the amount of salt recovered by each method to determine which method is most effective for separating salt from water.
