What is the Correct Molar Solubility for Barium Chromate and Silver Phosphate?

[mainzelmadchen]

Homework Statement

I have worked these two problems to the best of my knowledge and I keep getting the wrong answer (I'm not sure what the right answer is). Here are the questions:

1. At a certain temperature the solubility of barium chromate (BaCrO4) is 1.9×10-5 mol/L. What is the Ksp of BaCrO4 at this temperature?
2. What is the molar solubility of silver phosphate (Ag3PO4) in water? Ksp = 1.8×10-18.

Homework Equations

The relevant equations are Ksp=([products]/[reactants])

The Attempt at a Solution

For question 1: BaCrO₄⇔Ba²⁺ + CrO₄^2-
K_sp=[Ba²⁺][CrO₄^2-]/1 (since it is a solid)
K_sp=[x][x]=x²
K_sp=[1.9x10^-5]²=3.61x10^-10 = 3.6x10^-10

For question 2: Ag₃PO₄⇔3Ag⁺ + PO₄^3-
1.8x10^-18 = ([Ag⁺]³[PO₄^3-])/1
1.8x10^-18 = [3x]³[x]
1.8x10^-18 = [27x⁴] then divide both sides by 27
6.6666667x10^-20 = x⁴ then do the fourth root on both sides
x = 1.6068568x10^-5 = 1.6x10^-5

I would very much appreciate any insight into this. Thank you!

 

[Saitama]

Homework Statement

I have worked these two problems to the best of my knowledge and I keep getting the wrong answer (I'm not sure what the right answer is). Here are the questions:

1. At a certain temperature the solubility of barium chromate (BaCrO4) is 1.9×10-5 mol/L. What is the Ksp of BaCrO4 at this temperature?
2. What is the molar solubility of silver phosphate (Ag3PO4) in water? Ksp = 1.8×10-18.

Homework Equations

The relevant equations are Ksp=([products]/[reactants])

The Attempt at a Solution

For question 1: BaCrO₄⇔Ba²⁺ + CrO₄^2-
K_sp=[Ba²⁺][CrO₄^2-]/1 (since it is a solid)
K_sp=[x][x]=x²
K_sp=[1.9x10^-5]²=3.61x10^-10 = 3.6x10^-10

For question 2: Ag₃PO₄⇔3Ag⁺ + PO₄^3-
1.8x10^-18 = ([Ag⁺]³[PO₄^3-])/1
1.8x10^-18 = [3x]³[x]
1.8x10^-18 = [27x⁴] then divide both sides by 27
6.6666667x10^-20 = x⁴ then do the fourth root on both sides
x = 1.6068568x10^-5 = 1.6x10^-5

I would very much appreciate any insight into this. Thank you!

Your approach looks fine to me unless you have done some calculation mistake.

What are the correct answers?

 

[mainzelmadchen]

It is an online homework, like a quiz, that we are allowed multiple attempts on. It doesn't give me the correct answer. I'll email the prof. Thanks!

 

[drusman313]

where is this coming from? [27x4]

 

[Borek]

Which part of $(3x)^3x = 27x^4$ is unclear to you? This is a pretty basic algebra.