Chem (solubility of MF2, check my work)

The Ksp of magnesium fluoride is 6.4E-9. Calculate the solubility (in grams per liter) of magnesium fluoride in water.

MgF2 <---> Mg^2+(aq) + 2F^-(aq)
[Mg^2+] = x & [2F^-] = 2x

(x)(2x^2) = 6.4E-9
4x^3 = 6.4E-9
x^3 = 1.6E-9
x = 1.2E-3 [Mg^2+]
2x = [F^-] = 2.4E-3

?g MgF2/L = (1.2E-3 mol MgF2/L)(64.3018 g MF2/1 mol MgF2) = 8.4E-2g/L dissolved MgF2.

Again I have a feeling I messed somthing toward the final calculations. I used 1.2E-3 mol, which is really Mg^2+. I was following another example in book.


The Ksp of magnesium fluoride is 6.4E-9. Calculate the solubility (in grams per liter) of magnesium fluoride in water.

MgF2 <---> Mg^2+(aq) + 2F^-(aq)
[Mg^2+] = x & [2F^-] = 2x
No, you have let (MgF2) = x so (Mg^+2)=x and (F^-)= 2x NOT (2F^-)=2x. THE F^- is x. Twice the (F^-) would be 4x.
(x)(2x^2) = 6.4E-9
4x^3 = 6.4E-9
x^3 = 1.6E-9
x = 1.2E-3 [Mg^2+] This is also (MgF2).
2x = [F^-] = 2.4E-3
You see that 2x is (F^-) so you have done this step properly. Had you been consistent, then you would have said 2F^- = 4x. What you did was to make two errors but they compensated for each other and you have the correct answer for x, 2x, Mg and F.

?g MgF2/L = (1.2E-3 mol MgF2/L)(64.3018 g MF2/1 mol MgF2) = 8.4E-2g/L dissolved MgF2.

Again I have a feeling I messed somthing toward the final calculations. I used 1.2E-3 mol, which is really Mg^2+. Yes, you are correct but it also is the (MgF2). Although you didn't put that (I added it at the beginning). You do have an error in the molar mass of MgF2. I didn't do it exactly but it is closer to 62 something since Mg is about 24.3 and F is 19 each for 38 and 24.3 + 38 is about 62.3/ I was following another example in book. I hope this clears up the slight misunderstanding of the Ksp process.<




I had another thought which might help. Many students make the same mistake of calling (2F^-) = 2x and they will write
Ksp = (Mg^+2)(2F^-)^2 which is not correct.
It IS correct that since
MgF2 ==> Mg^+2 + 2F^-, then
(F^-)=(2Mg^+2) and since you called (MgF2) = x and (Mg^+2) = x; it should be obvious that (F^-) = (2Mg^2+)= 2x.

  1. 👍
  2. 👎
  3. 👁

Respond to this Question

First Name

Your Response

Similar Questions

  1. Chemistry

    A 3.214-g sample of magnesium reacts with 8.416g of bromine. The only product is magnesium bromide. If 1.934g of magnesium is left unreacted, how much magnesium bromide is formed? -Sorry, I've completely forgot how to do

  2. Chemistry

    Upon decomposition, one sample of magnesium fluoride produced 1.65kg of magnesium and 2.58kg of fluorine. A second sample produced 1.38kg of magnesium. How much fluorine (in grams) did the second sample produce?

  3. chemistry

    Suppose you tried to combine 42 grams of magnesium with 42 grams of oxygen. Which of the two substances would have some left after the reaction and how much magnesium oxide would be formed?

  4. Chemistry

    calculate the number of moles of magnesium chloride produced by reacting 168 grams of magnesium trioxocarbonate 4 with excess hydrochloric acid

  1. Chemistry

    Magnesium reacts with oxygen to form magnesium oxide according to the following equation: 2Mg(s) + O2(g) ==> 2MGO(s) If 0.81 grams of magnesium oxide are formed, how many grams of oxygen reacted?

  2. chem

    Magnesium hydroxide is produced by reacting magnesium oxide with excess water. If the reaction has an expected yield of 81%, how much magnesium oxide should be reacted to produce 98.0 g of magnesium hydroxide?

  3. chemistry

    When magnesium is heated in air, it reacts with oxygen to form magnesium oxide. 2Mg + O2 --> 2MgO If the mass of the magnesium increases by 0.335 g, how many grams of magnesium reacted? A. 0.882 B. 0.441 C. 0.509 D. 1.02 E. Not

  4. Chemistry

    Calculate the solubility (in g/L) of calcium fluoride in water at 25°C if the Ksp for is 1.5 × 10-10 .

  1. Chem

    (c) Using the appropriate Ksp value from Appendix D, calculate the solubility of Cu(OH)2 in grams per liter of solution. Appendix D: Ksp for Cu(OH)2 = 4.8 x 10-20 thanks!

  2. Science

    When magnesium oxide (MgO) and water (H20)react, they produce magnesium hydroxide Mg(OH)2. Magnesium hydroxide is a medicine used to treat an upset stomach. The equation for this chemical change is shown below: MgO + H20 -->

  3. chem

    Calculate the solubility of magnesium hydroxide (Mg(OH)2), ksp=1.1x10^-11? i have done this problem so many times and keep getting it wrong, i know the answer is 1.4x10^-4 but how do i get there? i did an ice chart and tried doing

  4. Chemistry - Stoichiometry

    16.2g of magnesium reacts exactly with 25.3g of fluorine to produce magnesium fluoride, the only product. How many grams of magnesium fluoride could be produced from the reaction of 10.5g of magnesium with excess fluorine. This is

You can view more similar questions or ask a new question.