Acidic & Basic Salt Solutions: Explanation & Examples

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  • 0:01 Introduction to Salt Solutions
  • 1:08 What Is a Salt?
  • 2:08 Acids and Bases
  • 3:57 Salt Solutions and pH
  • 6:09 Predicting pH of Salt…
  • 7:55 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.

In this video lesson, you will learn how to tell if a salt solution is acidic, basic, or neutral. You will find out how to recognize the effect of individual ions in solution and how they can change the pH. A short quiz will test your knowledge.

Introduction to Salt Solutions

Shelly is an ace chemist. She knows all about salt solutions. She has three beakers. Each one contains a different salt dissolved in water. To me, each beaker looks exactly the same, but Shelley will demonstrate that they are very different. Let's see what she does.

Three beakers with salt solutions
 three salt beakers

Shelley has tested the pH, or in other words, the acidity, of each solution. For Beaker 1, the litmus paper has come out red, so this is an acidic solution; the pH is less than 7. For Beaker 2, the paper has come out blue, so this is a basic solution; the pH is greater than 7. And for Beaker 3, the paper hasn't changed color at all, so this is a neutral solution; the pH equals 7.

Hmm, that is interesting. Shelley knew that there was a difference in the pH of each salt solution. So how did she know that?

What is a Salt?

Before we get to figuring out the pH of a salt solution, let's take a small step back and define a few important terms for you. Firstly, this lesson is all about salts. A salt is an ionic solid made up of two ions: a positive cation and a negative anion. The cation is any positive ion other than H+ and the anion is any negative ion other than OH- or O2-. A salt is formed by the reaction of an acid and a base and this is called a neutralization reaction.

Neutralization reaction
neutralization reaction

You can see the general reaction here where a salt is formed along with water. During a neutralization reaction, partners of the acids and bases swap. You can see that the salt is formed from the acid's sulfate ion and the base's ammonium ions. The two hydrogens and the hydroxides join together to form two moles of water.

Acids and Bases

You will soon see that the identity of the ions in the salt is our clue to predicting the pH of the salt solution. Each salt formed will vary according to the acid and base that formed it.

Okay, let us briefly think about acids and bases. The definition that works really well for us here is an acid is a molecule that donates hydrogen ions, or H+, and a base accepts hydrogen ions, H+. Acids and bases can also be described as strong or weak. And this has to do with how easily they can give up or accept hydrogen ions. Let me use a football analogy to help you with this.

Imagine that acids are the quarterbacks in a football team whose job is to get rid of the ball (H+). A strong acid, just like an awesome quarterback, delivers the ball well. On the other hand, a weak acid, like a poor quarterback, is often left holding the ball. Now imagine that the base is the wide receiver, whose job is to catch and hold onto the ball (H+). A strong base, like an awesome wide receiver, holds onto the ball. But a weak base, like a poor wide receiver, often drops the ball.

We need to be able to tell the difference between a strong and weak acid and base because of the effect it will have on the salt that is formed.

There are only a few strong acids and bases and these should be learned. Look at the table below.

Strong Acids HCl, HNO3, H2SO4, HBr, HI, HClO4
Strong Bases The hydroxides of the Group I metals and Ca(OH)2, Sr(OH)2

All other acids and bases except for these are considered weak.

Salt Solutions and pH

Okay, so now let's get back to salts. When a salt is dissolved in water, the ions separate from each other. Hydrolysis may occur if the ions react with the water molecules to produce H3O+ and OH- ions. Do not be confused by H3O+. It means the same thing as H+. We just recognize that H+ cannot hang out alone in water so it brings a water molecule with it. You can see that if the ions hydrolyze water and produce either H3O+ or OH- ions, this will affect the pH of the solution.

To predict whether a salt solution will be acidic, basic, or neutral, we have to consider the effect, if any, of the ions in solution. The key to this is whether the ions come from a strong or weak acid and a strong or weak base. Fortunately, there are some neat guidelines we can follow:

1. Salts that are from strong bases and strong acids DO NOT hydrolyze water and so the pH remains at 7. Our pass is completed and the reaction is totally neutralized.

2. Salts that are from strong bases and weak acids DO hydrolyze water, giving it a pH greater than 7. Here, the wide receiver is trying really hard to get that H+ and dominates the play.

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