Question

The solubility of calcium phosphate in water is x mol h at 25 Degree C. Its solubility product is equal to:
A. $108{{x}^{2}}$
B. $36{{x}^{3}}$
C. $36{{x}^{5}}$
D. $108{{x}^{5}}$

Answer 1

All phosphates are insoluble aside from those of sodium, potassium and ammonium. Some hydrogen phosphates, for example, $C{{a}_{3}}{{(P{{O}_{4}})}_{2}}$, are solvent. I) All sulfides are insoluble aside from those of ammonium, sodium, calcium, potassium, magnesium, barium and strontium. These are somewhat hydrolyzed in water .

Step by step answer: The solubility product, by definition, is the equilibrium constant for dissolution of a solid ionic compound to yield ions in solution (usually water). It is abbreviated Ksp.
The equation for dissolution of calcium phosphate$C{{a}_{3}}{{(P{{O}_{4}})}_{2}}$ in water is:
$C{{a}_{3}}{{(P{{O}_{4}})}_{2}}$= $3Ca(2+)+2P{{O}_{4}}(3-)$
and the equilibrium constant will be equal to:
Ksp = $\left[ Ca(2+) \right]\hat{\ }3*\left[ P{{O}_{4}}(3-) \right]\hat{\ }2$
Now, if you want to solve problems like how much calcium phosphate will dissolve in water you need to replace $\left[ Ca{{(}^{2+}}) \right]$and $\left[ P{{O}_{4}}{{(}^{3+}}) \right]$with something more beneficial. For every mole of$C{{a}_{3}}{{(P{{O}_{4}})}_{2}}$ when it dissolves, will yield 3 moles of (=3x) and 2 moles ofP{{O}_{4}}(3-)$$$$(=2x) so the Ksp expression becomes:
$\left[ Ca{{(}^{2+}}) \right]\hat{\ }3*\left[ P{{O}_{4}}{{(}^{3+}}) \right]\hat{\ }2=>(3x)\hat{\ }3*(2x)\hat{\ }2=108x\hat{\ }5$
Calcium phosphate is $C{{a}_{3}}{{(P{{O}_{4}})}_{2}}$ ​.
$C{{a}_{3}}{{(P{{O}_{4}})}_{2}}3C{{a}^{2+}}+2P{{O}_{4}}^{3-}$
$3x$ $2x$
${{K}_{sp}}={{\left[ 3x \right]}^{3}}{{\left[ 2x \right]}^{2}}=108{{x}^{5}}$

So, the correct option is D. $108{{x}^{5}}$

Additional Information: Elementary calcium reacts with water. Calcium compounds are more or less water soluble. Calcium carbonate has a solubility of, $14mg/L$ which is multiplied by a factor five in presence of carbon dioxide. Calcium phosphate solubility is$20mg/L$, and that of calcium fluoride is$16mg/L$.

Note: At ${{25}^{\circ }}C$ and $pH7.00$, Ksp for calcium phosphate is $2.07*{{10}^{-33}}$ , indicating that the concentrations of $C{{a}^{2+}}$ and $P{{o}_{4}}^{3-}$ ions in solution that are in equilibrium with solid calcium phosphate are very low.