Question

Determine the minimum concentration of the precipitating agent on the right to cause precipitation of the cation from the solution on the left.

3.5×10−2 M Ba(NO3)2;NaF Express your answer using two significant figures
8.0×10−2 M CaI2;K2SO4 Express your answer using two significant figures.
2.0×10−3 M AgNO3;RbCl Express your answer using two significant figures.

Answer 1

To find the minimum concentration of the precipitating agent that will cause precipitation, one must compare the ion product with the solubility product constant (Ksp) of the potential precipitate. Without knowing the Ksp values for the potential precipitates (like BaF2, CaSO4, or AgCl), it is not possible to calculate the specific minimum concentrations needed.

Step-by-step explanation:

To determine the minimum concentration of a precipitating agent required to cause precipitation of a cation from a solution, one must compare the ion product of the relevant ions with the solubility product constant (Ksp) for the precipitate that may form. If the ion product exceeds the Ksp, precipitation will occur. We'll apply this principle to work through each of the provided examples:

1. Ba(NO3)2 and NaF: The relevant reaction is Ba2+ + 2F- → BaF2. The Ksp for BaF2 needs to be known to proceed. However, since the Ksp is not provided and cannot be determined without additional information, we can't calculate the precise concentration of NaF required to begin precipitation.
2. CaI2 and K2SO4: The relevant reaction is Ca2+ + SO42- → CaSO4. Again, the Ksp for CaSO4 is needed to find the minimum concentration of precipitating agent K2SO4.
3. AgNO3 and RbCl: The reaction here is Ag+ + Cl- → AgCl. To find the minimum concentration of RbCl that will cause AgCl to precipitate, we use the Ksp for AgCl which is typically available in reference books.

It is important to have the Ksp values to solve these types of problems. Without them, we cannot determine the minimum concentration of the precipitating agent.