We’re being asked to determine which precipitate will form given in the given solutions for MgF2 and Ag2CrO4
For this, we need to compare the reaction quotient (Q) vs. the solubility product constant (Ksp). Recall that when:
• Q > Ksp: the solution is supersaturated and a precipitate will form. Reactants are favored.
• Q = Ksp: the solution is at equilibrium and no precipitate will form.
• Q < Ksp: the solution is unsaturated and no precipitate will form. Products are favored.
In this case, we need to follow each step:
Step 1. Setup the reaction quotient expression
Step 2. Determine the concentrations of each species involved in the precipitation
Step 3. Calculate for Q
Step 4. Compare it to Ksp
In which solution(s) will a precipitate form?
I. 0.00090 g of Na 2CrO 4 (molar mass = 162.0 g/mol) is added to 225 mL of 0.00019 M AgNO 3. Ksp Ag 2CrO 4 = 1.1 x 10 -12
II. 0.100L of 0.0015 M MgCl 2 and 0.200L of 0.012 M NaF. Ksp MgF 2 = 3.7 x 10 -8
a. I - no; II - no
b. I - yes; II - no
c. I - no; II - yes
d. I - yes; II - yes
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Our tutors have indicated that to solve this problem you will need to apply the Selective Precipitation concept. If you need more Selective Precipitation practice, you can also practice Selective Precipitation practice problems.
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