For the following questions, identify the ions comprising the salt, and then use

Question

For the following questions, identify the ions comprising the salt, and then use the expression for the solubility product to perform the necessary calculations. This simple exercise involves the assumptions that you can ignore any complications which might result as a consequence of the basicity or acidity of the ions, ion pairing, complex ion formation, or auto-ionization of water.

Calculate the concentration, in mol/L, of a saturated aqueous solution of Sr3(PO4)2 (Ksp = 1.00×10-31). mol/L

Calculate the solubility, in g/100mL, of Sr3(PO4)2. g/100mL

Calculate the mass of Ca5(PO4)3OH (Ksp = 6.80×10-37) which will dissolve in 100 ml of water.

Explanation / Answer

Sr3(PO4)2---------> 3Sr+2 +2PO4-3

let x- molar solubility of Sr3(PO4)2

then 2x= Sr+2 and Po4-3 =2x

KSp = (3x)3 *(2x)2= 1*10-31        x =2.47*10-7 moles/L

Molecular weight of Sr3(PO4)2 =453

2.47*10-7 moles/ L= 2.47*10-7*453 g/L=0.000111891 g/L

1000ml will have 0.000111891 gm

100ml will have 100*0.000111891/1000 =0.00001189 g

b)

Ca5(PO4)3OH <======> 5Ca (+2) + 3PO4 (-3) + OH-

KSp = (5x)5*(3x)3*x = 6.8*10-37, where x= moalr solubility of Ca5(Po4)3OH

x= 2.71*10-5 moles/ L = 2.71*10-5*501 gm/L ( Molar mass of Ca5(PO4)3 OH= 504) =0.0136 gm/L

1000 ml will have 0.0136 gm

100ml will have 0.0136*100/1000 =0.0136 gm

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