# Solubility Rule Question

## Homework Statement

Ok, so basically, our teacher gave us some solubility rules... then we did a problem where we mixed two solutions and checked to see if a precipitate would form.

So he calculated Qsp for one of the products and compared it to Ksp for that product, he did not calculate Qsp and Ksp and forth 'other'... this 'other' product obeyed the solubility rules.

So from what I understand, when you mix two solutions to see if a precipitate forms, you ignore the soluble products because they have infinite solubility?

I mean, do the solubility rules tell us that those substances have infinite solubility?

Quantum Defect
Homework Helper
Gold Member

## Homework Statement

Ok, so basically, our teacher gave us some solubility rules... then we did a problem where we mixed two solutions and checked to see if a precipitate would form.

So he calculated Qsp for one of the products and compared it to Ksp for that product, he did not calculate Qsp and Ksp and forth 'other'... this 'other' product obeyed the solubility rules.

So from what I understand, when you mix two solutions to see if a precipitate forms, you ignore the soluble products because they have infinite solubility?

I mean, do the solubility rules tell us that those substances have infinite solubility?
Nothing has infinite solubility.

If you look in tables (like in the CRC Handbook) you will see solubility data given, units will be something like grams per kg water, or grams per liter.

Borek
Mentor
In a way infinite solubility is miscibility. But its not about solids dissolved in liquids, but about liquids dissolved in liquids.

Ok. So infinite solubility doesn't exist, but in the original case mentioned, we ignore the soluble substance because its just way more soluble, correct?

Quantum Defect
Homework Helper
Gold Member
Ok. So infinite solubility doesn't exist, but in the original case mentioned, we ignore the soluble substance because its just way more soluble, correct?

Na+ salts are very soluble, nitrates are soluble, ... Some things are very soluble, many things are insoluble. Generally when you are trying to mix two liquids together, you will have an anion paired with something like sodium cation and a cation paired with something like nitrate. Mixing the two will give you e.g. "sodium nitrate" as one candidate for froming a precipitate (it won't because it si really soluble) and another candidate -- e.g. AgCl (like if you mixed silver nitrate with sodium chloride). As you do more of these things you will learn to recognize the likely culprit from the innocent bystander -- like any good detective!