When Does Solution Concentration Remain Constant?
Quick Answer
The concentration of a solution remains constant when the ratio of solute to solvent stays the same. For instance, removing an equal amount of both solute and solvent does not change the concentration.
Understanding solution concentration is fundamental in chemistry. The concentration of a solution is defined as the amount of solute (the substance being dissolved) present in a given amount of solvent (the substance doing the dissolving). The formula for calculating concentration is typically expressed as:
Concentration = Amount of solute (in moles) / Volume of solution (in liters)
To maintain a constant concentration, the ratio of solute to solvent must remain unchanged. One scenario where this occurs is when you remove an equal volume of both solute and solvent from a solution.
For example, consider a saltwater solution containing 5 grams of salt dissolved in 100 milliliters of water. The concentration can be calculated as follows:
Concentration = 5 grams / 100 mL = 0.05 grams/mL
If you were to pour out 20 milliliters of this solution, you would also need to remove a proportional amount of salt. Since there are 5 grams of salt in 100 mL, removing 20 mL means you would remove 1 gram of salt (20 mL is 20% of 100 mL).
After this removal, you would have 4 grams of salt in 80 mL of water:
Concentration = 4 grams / 80 mL = 0.05 grams/mL
As shown, the concentration remains constant even after removing both solute and solvent.
However, if you were to add more solvent (like water) without adding more solute, the concentration would decrease. For instance, if you added an additional 20 mL of water to the previous example, the concentration would now be:
Concentration = 5 grams / 120 mL = 0.0417 grams/mL
Conversely, if you add more solute (like salt) without changing the volume of solvent, the concentration would increase. For example, adding an extra 1 gram of salt to the initial 5 grams in 100 mL would result in:
Concentration = 6 grams / 100 mL = 0.06 grams/mL
In conclusion, maintaining a constant concentration requires keeping the ratio of solute to solvent the same. This concept is crucial in various applications, from cooking to pharmaceuticals, where precise concentrations are necessary for desired reactions or flavors. Understanding these principles can help students grasp the foundational concepts of chemistry and their real-world applications.
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