A---When 12.0 mL of a 2.72×10 -4 M sodium hydroxide solution is combined with 25

Question

A---When 12.0 mL of a 2.72×10-4 M sodium hydroxide solution is combined with 25.0 mL of a 1.70×10-4 M magnesium chloride solution does a precipitate form?

For these conditions the Reaction Quotient, Q, is equal to?

B---When 18.0 mL of a 8.91×10-4 M zinc fluoride solution is combined with 12.0 mL of a 9.92×10-4 M sodium carbonate solution does a precipitate form?

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

C---When 22.0 mL of a 8.12×10-4 M sodium sulfate solution is combined with 18.0 mL of a 5.28×10-4 M barium acetate solution does a precipitate form? (yes or no)

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

Explanation / Answer

A)

[OH-] = 12 x 2.72 x 10^-4 / (12 +25) = 8.82 x 10^-5 M

[Mg+2] = 25 x 1.70 x 10^-4 / (12 +25) = 1.15 x 10^-4 M

Qsp = [Mg+2][OH-]^2 = (1.15 x 10^-4)(8.82 x 10^-5)^2

Qsp = 8.94 x 10^-13 =Quotient Q

Ksp of Mg (OH)2 = 5.61 x 10^-12

Ksp > Qsp . so there is no precipitate is formed

B)

When 18.0 mL of a 8.91×10-4 M zinc fluoride solution is combined with 12.0 mL of a 9.92×10-4 M sodium carbonate solution does a precipitate form?
[Zn+2] = 18 x 8.91 x 10^-4 / 30 = 5.35 x 10^-4 M

[CO3-2] = 12 x 9.92 x 10^-4 / 30 = 3.97 x 10^-4 M

Quotient, Q, = 5.35 x 10^-4 x  3.97 x 10^-4 = 2.12 x 10^-7

Ksp of ZnCO3 = 1.46 x 10^-10

Q > Ksp . so the precipitate will form

C )

BaSO4 , Q from the data = 1.06 x 10^-7

Q = 1.06 x 10^-7

Ksp = 1.08 x 10^-10

Q > Ksp

so precipitate will form

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