Solubility of Common Salts: Predicting Reaction Outcomes

Solubility of Common Salts: Predicting Reaction Outcomes
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  • 0:01 Introduction to Solubility
  • 0:38 What Is a Salt?
  • 2:59 Solubility Rules
  • 4:26 Predicting Reaction Outcomes
  • 7:37 Lesson Summary
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Lesson Transcript
Instructor: Nicola McDougal

Nicky has taught a variety of chemistry courses at college level. Nicky has a PhD in Physical Chemistry.

Ever wondered why some salts dissolve in water and others don't? In this lesson you will learn about some simple salt solubility rules. Using these rules, you will be able to predict the products of many chemical reactions.

Introduction to Solubility

Let me introduce you to Shelley. Shelley is a really ace chemist; she can mix two colorless solutions and produce a bright yellow solid. Cool, it's magic!

Actually it isn't really magic at all, although it is still cool. You see, Shelley understands all about the solubility of common salts. She knew exactly what two colorless solutions to mix together to produce a yellow solid. Not only that, but she also knew just what was going on in the reaction. And by the end of this lesson, you will too.

What is a Salt?

Before we get to reactions, let's take a small step back and define a few important terms for you. Firstly, this lesson will be all about salts. A salt is an ionic compound and it is made up of two ions -- a positive cation and a negative anion.

Here you can see a number of different salts of sodium.


Each salt consists of a positive ion, the sodium, and a negative ion. Now you probably already know that sometimes the anion can contain more than one type of atom. For example, the final three molecules here are sodium hydroxide, sodium cyanide and sodium acetate. The different colors show you there is more than one type of atom in the anion. We call these anions polyatomic ions.

Shelley is going to demonstrate what happens when she puts a teaspoon of solid NaCl, or sodium chloride, into water.

I am pretty sure you predicted this would happen: the solid NaCl completely dissolves in the water. We say that sodium chloride is soluble in water, meaning it breaks down into cations and anions, forming a sodium chloride solution. You can't see the individual sodium and chloride ions because they are so tiny, but we know this happens because we can conduct electricity through a sodium chloride solution.

When sodium chloride is dissolved in water, the equation is: NaCl --> Na+(aq) + Cl-(aq). The equation tells us that solid sodium chloride has broken down into aqueous ions of Na+ and Cl-. These little aq symbols here are very important, as you will see later in the lesson.

It turns out that not all salts are soluble in water, and sometimes when solutions of two different salts are mixed together, an insoluble solid is formed. This is just like the magic Shelley showed us at the beginning of the lesson. The precipitate that forms is an insoluble solid salt separating from the solution.

What is really awesome is that we can use our understanding of salt solubility to predict what will happen in a reaction between two different salt solutions. And we will look at this next.

Solubility Rules

Now, there are some pretty neat rules we can use to predict solubility. For this lesson, we are going to simply say that something is soluble or insoluble. As you go to higher levels of chemistry, you will also consider salts that are only slightly soluble. But for now, let's keep it simple.

Water Solubility of Common Salts

Ions Solubility of salts Solubility Exceptions
sodium (Na), potassium (K) and ammonium (NH4+) all soluble none
nitrates (NO3-) all soluble none
chlorides (Cl-) and iodides (I-) most soluble silver (Ag+), lead (Pb2+), mercury (Hb22+)
sulfates (SO42-) most soluble Ag+, Pb2+, calcium Ca2+, strontium (Sr2+) and barium (Ba2+)
carbonates (CO32-) most insoluble Group 1A, NH4+ soluble
hydroxide (OH-) most insoluble Group 1A, NH4+ soluble

So, here we can see a table divided into groups of ions. You'll be pleased to know that you do not need to remember this table, just how to use it. It is important to notice the exceptions. We can say most chlorides and iodides are insoluble, but there are exceptions to this rule.

It is important you realize this table only shows a few ions as an example. In your studies, you may be given a table that contains other ions as well. Don't worry about this because the way you use it will be just the same.

This table comes in really useful if we want to predict whether a precipitate will form during an ionic reaction between two different salt solutions. Recall that when ionic compounds react together, we call this a double replacement reaction. In other words, two elements in different compounds replace each other. It is just like swapping dance partners in a dance.

So, let us have a go at predicting the outcome of two reactions of salt solutions.

Predicting Reaction Outcomes

Let us predict what will happen when Shelley mixes together ammonium phosphate and potassium carbonate. Do we think a precipitate will form?

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