How can the conductivity of a salt solution be decreased?
A. Add more salt to increase the concentration.
B. Add more water to decrease the concentration.
C. Add more water to increase the concentration.
D. Add more salt to decrease the concentration.
The Correct Answer and Explanation is :
The correct answer is B. Add more water to decrease the concentration.
Explanation
The conductivity of a salt solution is largely influenced by the concentration of ions present in the solution. When salts dissolve in water, they dissociate into positive and negative ions, which are responsible for conducting electricity. The higher the concentration of these ions, the greater the conductivity of the solution.
1. Ion Concentration and Conductivity:
Conductivity is a measure of how well a solution can conduct electric current, which is dependent on the presence of charged particles (ions). In a salt solution, such as sodium chloride (NaCl), when the salt dissolves, it breaks into Na⁺ and Cl⁻ ions. The more ions present in the solution, the higher the conductivity.
2. Dilution Effect:
When more water is added to the salt solution, the total volume of the solution increases while the amount of salt (and thus the number of ions) remains constant. This dilution decreases the concentration of ions in the solution, thereby reducing the solution’s overall conductivity. For example, if you have a highly concentrated salt solution and you add water, the concentration of Na⁺ and Cl⁻ ions decreases, leading to lower conductivity.
3. Other Options:
- Option A (Add more salt to increase the concentration) would actually increase the conductivity because it adds more ions to the solution.
- Option C (Add more water to increase the concentration) is incorrect because adding water does not increase the concentration of ions; it dilutes them.
- Option D (Add more salt to decrease the concentration) is also incorrect as adding more salt increases the concentration of ions.
In summary, to decrease the conductivity of a salt solution, adding more water is the most effective method because it lowers the concentration of dissociated ions in the solution, resulting in reduced conductivity.