Question

A solution of 0.1 L of 0.3 M Ca(NO3)2 is mixed with 0.2 L of 0.06 M NaF. Calculate the reaction quotient Qsp. Does calcium fluoride precipitate? (Ksp (CaF2) = 3.2×10–11). (A) Qsp = 1.6×10–4; no precipitate. (B) Qsp = 1.6×10–4; a precipitate will form. (C) Qsp = 3.2×10–11; no precipitate. (D) Qsp = 3.2×10–11; a precipitate will form. (E) Qsp = 3.2×10–7; no precipitate.

Answer 1

Correct answer is : (B.) Q_sp = 1.6 x 10^-4 ; a precipitate will form

Explanation

Concentration Ca(NO₃)₂ = 0.3 M

volume Ca(NO₃)₂ = 0.1 L

moles Ca(NO₃)₂ = (Concentration Ca(NO₃)₂) * (volume Ca(NO₃)₂)

moles Ca(NO₃)₂ = (0.3 M) * (0.1 L)

moles Ca(NO₃)₂ = 0.03 mol

final volume = 0.1 L + 0.2 L = 0.3 L

final concentration of Ca(NO₃)₂ = (moles Ca(NO₃)₂) / (final volume)

final concentration of Ca(NO₃)₂ = (0.03 mol) / (0.3 L)

final concentration of Ca(NO₃)₂ = 0.1 M

Similarly, final concentration of NaF = 0.04 M

Reaction quotient, Q_sp = [Ca²⁺][F^-]²

Q_sp = (0.1 M) * (0.04 M)²

Q_sp = 1.6 x 10^-4

Since Q_sp > K_sp, therefore, precipitate will form.