Question

1A: Consider these compounds:

A. PbF2
B. Ni(CN)2
C. FeS
D. CaSO4
Complete the following statements by entering the letter(s) corresponding to the correct compound(s). (If more than one compound fits the description, include all the relevant compounds by writing your answer as a string of characters without punctuation, e.g, ABC.)
Without doing any calculations it is possible to determine that magnesium hydroxide is more soluble than __________, and magnesium hydroxide is less soluble than _______.
It is not possible to determine whether magnesium hydroxide is more or less soluble than_______ by simply comparing Ksp values.
1B: For each of the salts on the left, match the salts on the right that can be compared directly, using Ksp values, to estimate solubilities.
(If more than one salt on the right can be directly compared, include all the relevant salts by writing your answer as a string of characters without punctuation, e.g, ABC.)
1. nickel(II) hydroxide
A. Fe(OH)2
2. silver chloride
B. PbS
C. AlPO4
D. MnS
Write the expression for K in terms of the solubility, s, for each salt, when dissolved in water.
nickel(II) hydroxide
silver chloride
Ksp=_______
Ksp=________
Note: Multiply out any number and put it first in the Ksp expression. Combine all exponents for s.

Answer 1

Compound Ksp

`$PbF_2$`
`$3.3 * 10^(-8)$`

`$Ni(CN)_2$`
`$3 * 10^(-23)$`

FeS
`$8 * 10^(-19)$`

`$CaSO_4$`
`$4.93 * 10^(-5)$`

`$Mg(OH)_2$`
`$5.61 * 10^(-12)$`

Ksp of
`$Ni(CN)_2 << Ksp \text{ of}\ \ Mg(OH)_2$` and both compounds dissociate the same way. Hence
`$Mg(OH)_2$` is more soluble than
`$(B). \ Ni(CN)_2$`

`$Mg(OH)_2$` is less soluble than
`$(A). \ \ PbF_2 \ ()Ksp \ PbF_2 > Ksp \ \text{ of } \ Mg(OH)_2$`

It is not possible to determine CD -
`$FeS \text{ or} \ CaSO_4$` is more or less soluble than
`$Mg(OH)_2$` as though they have a different Ksp values their molecular dissociation is also different and they may have a close solubility values.

`$Ni(OH)_2$` can be directly compared with PbS,
`$AlPO_4, MnS$`

`$\text{For } \ Ni(OH)_2$`

`$AB_2(s) \rightarrow A^(2+) + 2B^(-)$`

`$Ni(OH)_2(s) \rightarrow Ni^(2+) + 2OH^-$`

100

1-s s 2s

Ksp =
`[A2+][B-]^2 = s * (2s)^2 = 4s^3`

Hence they can be directly compared by Ksp values, smaller the Ksp, smaller the solubility.

For Silver Chloride

`$AB(s) \rightarrow A^(x+)+B^(x-)$`

`$AgCl(s) \rightarrow Ag^+ + Cl^-$`

1 0 0

1 - s s s

Ksp
`$=[A^(x+)][B^(x-)]=s * s = s^2$`

Hence, they can be directly compared by Ksp values, smaller the Ksp, smaller the solubility.