Magnesium fluoride dissolves in water to the extent of 8.0 10-2 g/L at 25°C. Calculate the solubility of MgF2(s) in moles per liter, and calculate Ksp for MgF2 at 25°C.
I keep getting the same answer...please help!
It would have been far easier if you had posted your work, then I could have found the error.
MgF2 ==> Mg^2+ + 2F^-
solubility MgF2 = moles/L.
moles = 0.08/molar mass MgF2.
Ksp = (Mg^2+)(F2^-).
Substitute and solve for Ksp. Post your work if you still have trouble. The most common mistake made by students on a problem such as this is not multiplying MgF2 by 2 to obtain F^-, then not squaring the F^-.
To calculate the solubility of MgF2 in moles per liter (mol/L), we need the molar mass of MgF2 and the solubility in grams per liter (g/L).
The molar mass of MgF2 can be calculated by summing the atomic masses of magnesium (Mg) and fluorine (F):
MgF2 = (1 * Mg) + (2 * F) = 24.31 g/mol + (2 * 18.99 g/mol) = 62.31 g/mol
Given that the solubility of MgF2 in water is 8.0 * 10^-2 g/L, we can now calculate the solubility in moles per liter:
Solubility (in mol/L) = Solubility (in g/L) / Molar mass (in g/mol)
Solubility (in mol/L) = (8.0 * 10^-2 g/L) / (62.31 g/mol)
Evaluating this calculation, we get:
Solubility (in mol/L) = 1.285 * 10^-3 mol/L
Now, to calculate Ksp for MgF2 at 25°C, we need to use the solubility value obtained in the previous step.
The solubility product constant (Ksp) expression for MgF2 is as follows:
Ksp = [Mg2+][F-]^2
Since the stoichiometry of MgF2 is 1:2 (1 Mg2+ ion and 2 F- ions), the concentration of Mg2+ and F- will be the same.
Therefore,
Ksp = [Mg2+] * ([F-]^2)
= (1.285 * 10^-3 mol/L) * ((1.285 * 10^-3 mol/L)^2)
= 2.084 * 10^-9 mol^3/L^3
Thus, the calculated solubility of MgF2 in moles per liter is 1.285 * 10^-3 mol/L and the calculated Ksp for MgF2 at 25°C is 2.084 * 10^-9 mol^3/L^3.
If you keep getting the same answer, please ensure that you are using the correct molar mass and the correct solubility value in the calculations. Also, double-check the stoichiometry of the compound and the Ksp expression to avoid any mistakes.