Question

a) When 15.0 mL of a 4.60×10^-4 M silver fluoride solution is combined with 25.0 mL of a 3.28×10^-4 M potassium sulfate solution does a precipitate form? _____ (yes or no)

For these conditions the Reaction Quotient, Q, is equal to _____ .

b) When 18.0 mL of a 9.58×10^-4 M sodium carbonate solution is combined with 22.0 mL of a 4.65×10^-4 M copper(II) acetate solution does a precipitate form? _____(yes or no)

For these conditions the Reaction Quotient, Q, is equal to _____.

Answer 1

After mixing AgF and K₂SO₄  solution volume of solution becomes ( 15.0 + 25.0 = 40.0 ) .Hence , concentrations of AgF and K₂SO₄ changes. The new concentrations are calculated by using dilution formula as

M _Stock x V _stock = M _Dilute x V _Dilute

M _{Dilute =} M _Stock x V _stock /  V _Dilute  

M AgF = 4.60 x 10 ^-04 M x 15.0 ml / 40.0 ml

= 1.725 x 10 ^-04 M

= [Ag ⁺]

M K₂SO₄ = 3.28 x 10 ^-04 M x 25.0 ml / 40.0 ml

= 2.05 x 10 ^-04 M

=  [SO ₄^2-]  

Consider reaction : Ag₂SO_{4 (s)}   2 Ag ⁺_(aq) + SO ₄^2-_(aq)  

K sp = [Ag ⁺] ²  [SO ₄^2-] = 1.2 x 10 ^-05

Q = [Ag ⁺] ²  [SO ₄^2-]

= ( 1.725 x 10 ^-04 ) ² x ( 2.05 x 10 ^-04)

Q= 6.10 x 10 ^-12

Q < K sp , Hence NO precipitation .

2)

After mixing Sodium carbonate and copper acetate  solution volume of solution becomes ( 18.0 + 22.0 = 40.0 ) .Hence , concentrations of Sodium carbonate and copper acetate changes. The new concentrations are calculated by using dilution formula as

M _Stock x V _stock = M _Dilute x V _Dilute

M _{Dilute =} M _Stock x V _stock /  V _Dilute  

   M Na₂CO₃ = 9.58 x 10 ^-04 M x 18.0 ml / 40.0 ml

= 4.311 x 10 ^-04 M

= [CO₃^2- ]

M Cu(CH₃COO)₂ = 4.65 x 10 ^-04 M x 22.0 ml / 40.0 ml

= 2.56 x 10 ^-04 M

= [Cu ²⁺]

Consider reaction : CuCO_{3 (s)}   Cu ²⁺_(aq) + CO₃^2-_(aq)  

K sp = [Cu ²⁺][CO₃^2- ] = 2.5 x 10 ^-10

Q = [Cu ²⁺][CO₃^2- ]

= ( 2.56 x 10 ^-04 ) x ( 4.311 x 10 ^-04)

Q= 1.10 x 10 ^-07

Q > K sp , Hence precipitation takes place.