Question

Predict whether each of the following compounds is soluble in water: (a) \(\mathrm{Ni}(\mathrm{OH})_{2}\), (b) \(\mathrm{PbBr}_{2}\), (c) \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) (d) \(\mathrm{AlPO}_{4},(\mathrm{e}) \mathrm{AgCH}_{3} \mathrm{COO}\)

Short answer

(a) \(Ni(OH)_2\) is insoluble in water. (b) \(PbBr_2\) is insoluble in water. (c) \(Ba(NO_3)_2\) is soluble in water. (d) \(AlPO_4\) is insoluble in water. (e) \(AgCH_3COO\) is soluble in water.

Step-by-step solution

(a) Solubility of \(Ni(OH)_2\)

According to rule 6, hydroxides are generally insoluble except those of alkali metals, ammonium, calcium, barium, and strontium. Since nickel (Ni²⁺) is not one of these exceptions, \(Ni(OH)_2\) is insoluble in water.

(b) Solubility of \(PbBr_2\)

According to rule 3, bromides are soluble except for those of silver, lead, and mercury(I). Since the compound is a lead (Pb²⁺) bromide, \(PbBr_2\) is insoluble in water.

(c) Solubility of \(Ba(NO_3)_2\)

According to rule 2, all nitrates are soluble in water. Therefore, \(Ba(NO_3)_2\) is soluble in water.

(d) Solubility of \(AlPO_4\)

According to rule 5, all phosphates are generally insoluble except those of alkali metals and ammonium. Since aluminum (Al³⁺) is not an alkali metal or ammonium, \(AlPO_4\) is insoluble in water.

(e) Solubility of \(AgCH_3COO\)

According to rule 2, all acetates are soluble in water. Therefore, \(AgCH_3COO\) is soluble in water.

Key concepts

Hydroxides

Let's dive into the world of hydroxides, easy to grasp once you know the solubility rules. In general, hydroxides are infamous for being insoluble in water. This is true for most, except for some special cases you should remember:

• Hydroxides of alkali metals (like sodium and potassium) are noticeably soluble.
• Hydroxides containing ammonium (NH₄⁺), calcium (Ca²⁺), barium (Ba²⁺), and strontium (Sr²⁺) also dissolve in water fairly well.

Take nickel hydroxide, \(\mathrm{Ni(OH)}_{2},\): it's not on the list of exceptions. That means it won't dissolve in water. So, unless it's one of the lucky few I've just mentioned, hydroxide compounds prefer to stay out of the mix.

Nitrates

Nitrates are the life of the party when it comes to solubility. If you ever find yourself wondering whether a nitrate compound is soluble, just remember: they all are! With no exceptions, nitrates break from the usual constraints of solubility rules. For instance, in the case of \(\mathrm{Ba(NO}_{3})_{2},\) it's no surprise that this compound readily dissolves in water.

• This makes nitrates particularly handy in applications like fertilizers and explosives, where solubility is a vital property.

You can always count on nitrates for a dependable soluble experience.

Phosphates

Phosphates tend to be a bit more anti-social like hydroxides. Generally, phosphates are insoluble in water with notable exceptions. These exceptions include

• phosphates of alkali metals like sodium phosphate (Na₃PO₄)
• phosphates with ammonium (NH₄⁺)

Aluminum phosphate, \(\mathrm{AlPO}_{4},\) however, doesn't make it to the guest list. This compound stays out of the water, showing off its insoluble nature. Despite their tendency to retreat from solution, phosphates play a big role in biology, especially in energy transfer through ATP.

Acetates

Acetates are friendly fellows when it comes to solubility. Much like nitrates, all acetates enjoy mixing into water, making them completely soluble. Silver acetate, \(\mathrm{AgCH}_{3}\mathrm{COO},\) follows this friendly pattern and readily dissolves. This property makes acetates useful in scent and flavorings, given their ease to dissolve in liquids.

• Remember, no exceptions exist for acetates in terms of solubility – they all love to go for a swim.

So, whether you're dealing with sodium acetate or silver acetate, expect a solution every time!

Bromides

Bromides generally lean towards being soluble, but they have a few notable exceptions. While most will dissolve without putting up a fight, bromides of certain metals stand their ground.

• Insoluble bromides include ones combined with silver (Ag⁺), lead (Pb²⁺), and mercury (Hg₂²⁺).

Take lead bromide, \(\mathrm{PbBr}_{2},\) for example. It doesn't dissolve in water due to lead's reputation for resisting solubility with bromide. These few exceptions are important to remember last-minute for chemistry tests.