Question

MgF₂(s) <--> Mg²⁺(aq) + 2 F^–(aq)

In a saturated solution of MgF₂ at 18 ⁰C, the concentration of Mg²⁺ is 1.21 x 10^–3 molar. The equilibrium is represented by the equation above.

(a) Write the expression for the solubility-product constant, K_sp, and calculate its value at 18 ⁰C.

(b) Calculate the equilibrium concentration of Mg²⁺ in 1.000 liter of saturated MgF₂ solution at 18 ⁰C to which 0.100 mole of solid KF has been added. The KF dissolves completely. Assume the volume change is negligible.

(c) Predict whether a precipitate of MgF₂ will form when 100.0 milliliters of 3.00 x 10^–3 molar Mg(NO₃)₂ solution is mixed with 200.0 milliliters of a 2.00 x l0^–3 molar NaF solution at 18 ⁰C. Calculations to support your prediction must be shown.

(d) At 27 ⁰C the concentration of Mg²⁺ in a saturated solution of MgF₂ is 1.17 x 10^–3 molar. Is the dissolving of MgF₂ in water an endothermic or an exothermic process? Give an explanation to support your conclusion.  

Answer 1

Ksp - L MgE (5) = Mg2+ (aq) + 2 f (aq). the equation of solubility product is- Doillot Sp. [Mg2+] [F-] 3 no wond ziews (1.21x1013) (2.42x10-) 5 vab 37.09 X10-9 (ans). o ldiovo ) noto portiu b) Let, .. otevob pretproda is the concentration of nation or w then 2 is the concentration of 103 ev frion (by equilibrium ro to en in [Mg2+] = xm next w ith di [f- ] a co. 100 +2x) M ( Because of 0.1000 mole According to question courme of solid KF change in negligible and has been added) x is very smant number them co. 100+22) no 100 Now, kop = x (0.100) = 1.09810-9 X 27.09x10-7 the equilibrium concentration id= to F.09 xlorf

& of Accom According to question- [Mg2+] = 3:00x10 -3 m x 1000 me 3000 m2 21.00 x 103 m [F] = 2.00 x 10-3Mx 200 me 3oome 2 1.33x163M trial Kep = (1oox 10-3) (1.338 10-3) 2 21.78 x 10-9 So from the trial value, we can conclude no ppt. occurs - due to Itria kep a kap At 18°c, 1:21x10-3 m Maf dissolves at 24c, 117x103rd ragfy dissolves Mgf2 — Mg 2+ 2ftheat dissolving is exotheremic; if heat is increased according to Lachatelien's principle the requilibrium shift to left and ress Mgr. will dissove.