Monday, November 16, 2020

Solubility and Double Replacement

 General Chemistry Index

Where are we going with this? This page will assist in developing the ability to describe, classify, and give examples of various kinds of reactions: synthesis (i.e., combination), decomposition, single displacement, double displacement, acid/base, and combustion.

Solubility and Double Replacement

Part of predicting products of chemical reactions is determining if it will even react. One of the rules regarding the potential of a double replacement reaction to react is solubility of the products.

The complete set of predictors for if something will react in a double replacement situation is…

  • one of the products is water (H2O), 
  • one of the products is a common gas (H2S, H2CO3, H2SO3 and NH4OH), 
  • one of the products is is an insoluble solid (an example could be BaSO4)

There it is… Solubility… Right smack in the rules! Understanding solubility is fundamental to one of the rules that is part of figuring out if a double replacement reaction will occur!

  • So, what is solubility in the context of chemistry?

  • Solubility is the property of a solid, liquid or gaseous chemical substance called solute to dissolve in a solid, liquid or gaseous solvent. It is the state of a substance of being soluble(being able to dissolve)

  • Solubility refers to how well a substance dissolves in water. If a substance when placed in water dissolves then that substance is soluble. If it does not dissolve then it is not soluble.  

  • Solubility is the ability of a substance or the solute to dissolve in the solvent.

  • Solubility is the measure of how much a substance can dissolve in a gas, liquid, or solid substance. The thing that is being dissolved is the solute and the thing it dissolves in is the solvent. 

The concept of solubility should be fairly familiar to anyone. There are examples of things that dissolve and things that don’t around every home.

For instance, these things will dissolve in water:

  • Sugar
  • Salt 
  • Alka-Seltzer
  • Honey 

Of course, not everything will dissolve in water. Just to list a few things that won't…

  • Coffee grounds
  • Flour
  • Tea leaves
  • Pepper
  • Sand 
  • Paraffin wax
  • Oil 

There is a word for not being able to dissolve: insoluble. Just to complete the thought, there ought to be a definition.

Insoluble: the property of a substance (solid) meaning that will not dissolve in a solvent even after mixing.

An insoluble substance won't dissolve in a solvent after letting it sit and mix

Before we get back to predicting reaction products, we should make sure we know all the fancy words! Talking about soluble and insoluble falls into the context of solutions, so let’s get those defined.

Solution: A special type of homogeneous mixture composed of two or more substances.

Solute: A substance that is dissolved in a solution 

Solvent: substance, ordinarily a liquid, in which other materials dissolve to form a solution

Insoluble Solids and Predicting Products of
Double Replacement / Displacement Reactions

Okay, now that we know what we are talking about we can get back to that prediction of products thing…

First you have to realize you are dealing with a double replacement reaction. That’s pretty easy. Typically, double replacement reactions start off with two compounds and end up with two different compounds 

Double Replacement/Displacement reactions fit into “normal” form…

AB + CD = AC + BD 


AY + BX = AX + BY  

For instance, here are some examples of double replacement reactions:

AgNO3 + NaCl → AgCl + NaNO3 

BaCl2 + Na2SO4 --> BaSO4 + 2NaCl 

So, figuring out what kind of reaction it might be is done. The next question is “Will it actually react?” 

Answering that requires looking at the potential products and figuring out if they fit the rules. And one of those rules (described above) has to with solubility:

  • one of the products is is an insoluble solid (an example could be BaSO4)

That means that, somehow, you have to know if something is soluble or not. That means, not only must you realize it is a double replacement reaction, but that you also must figure out if the product (if not water and not a gas) is soluble. There should be rules or something? Surely?


1. Salts containing Group I elements (Li+, Na+, K+, Cs+, Rb+) are soluble. There are few exceptions to this rule. Salts containing the ammonium ion (NH4+) are also soluble.

2. Salts containing nitrate ion (NO3-) are generally soluble.

3. Salts containing Cl -, Br -, or I - are generally soluble. Important exceptions to this rule are halide salts of Ag+, Pb2+, and (Hg2)2+. Thus, AgCl, PbBr2, and Hg2Cl2 are insoluble.

4. Most silver salts are insoluble. AgNO3 and Ag(C2H3O2) are common soluble salts of silver; virtually all others are insoluble.

5. Most sulfate salts are soluble. Important exceptions to this rule include CaSO4, BaSO4, PbSO4, Ag2SO4 and SrSO4 .

6. Most hydroxide salts are only slightly soluble. Hydroxide salts of Group I elements are soluble. Hydroxide salts of Group II elements (Ca, Sr, and Ba) are slightly soluble. Hydroxide salts of transition metals and Al3+ are insoluble. Thus, Fe(OH)3, Al(OH)3, Co(OH)2 are insoluble.

7. Most sulfides of transition metals are highly insoluble, including CdS, FeS, ZnS, and Ag2S. Arsenic, antimony, bismuth, and lead sulfides are also insoluble.

8. Carbonates are frequently insoluble. Group II carbonates (CaCO3, SrCO3, and BaCO​3) are insoluble, as are FeCO3 and PbCO3.

9. Chromates are frequently insoluble. Examples include PbCrO4 and BaCrO4.

10. Phosphates such as Ca3(PO4)2 and Ag3PO4 are frequently insoluble.

11. Fluorides such as BaF2, MgF2, and PbF2 are frequently insoluble.


You’re probably thinking… “That’s a lot of stuff to sift through! Someone should create a chart!”

The following list indicates some common compounds and whether or not they are soluble–and also which of the rules apply.


Soluble or Insoluble




Covalent bonds in water are stronger than ionic bonds in salt 



No rules satisfied



Ba ion and Sulphate ion are large in size



Carbonates are insoluble.






The reaction is exothermic in that heat and Carbonic acid are produced. Carbonic acid is unstable so breaks up into carbon dioxide and water.



Salts containing this anion are called nitrates.  Almost all nitrates are soluble in water. 



Many ionic solids do not dissolve in water



Exception to the sulfide rule, calcium is the exception. 

Okay, what are you supposed to do with this information?

Since formation of an insoluble compound is one of the rules to predict if a double replacement/displacement reaction will occur…

(Remember those three rules?)

  • one of the products is water (H2O), 
  • one of the products is a common gas (H2S, H2CO3, H2SO3 and NH4OH), 
  • one of the products is is an insoluble solid (an example could be BaSO4)

…you can use the information presented and the chart to see if the reaction satisfies the rule about insoluble solids.

For example, these two reactions will occur because one of the products is insoluble in water.

Na2SO4 + Ba(NO3)2 → BaSO4 + 2 NaNO3 (the BaSO4 is insoluble)

2NaOH(aq) + FeCl2(aq) → 2NaCl(aq) + Fe(OH)2(s) 

On the other hand, this reaction will not

Sr(NO3)2+KCl → NR

Okay… the point should be made! Right? 

Double replacement / displacement reactions are plentiful, and it’s super easy to come up with combinations of compounds that won’t react.


The rules on this page should go a long way in helping predict if they will or not. Of course, chemistry has plenty of exceptions, but the information here is a solid starting point.



This document was written collaboratively by the Fourth Period Lowell High School 2020 Honors Chemistry Class and redacted by the site operator

Brian Bright - Lowell High School, 2023

Bill Snodgrass - University of Memphis, 1985, 1991, 2000

Sophia Emery - Lowell High School, 2023

Logan Ritter- Lowell High School, 2022

Walter Kotlin - Lowell High School, 2023

Madelyn Logan - Lowell High School, 2023

Isabelle McPheron - Lowell High School, 2022

Kayanna Seely - Lowell High School,  2023

Payton Gard- Lowell high school, 2022

Jakob Gricus - Lowell High School, 2023

Shelby Hilliard - Lowell High School, 2022

Liv Tully- Lowell High School, 2022

Josh Babin- Lowell High School, 2023

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