Acids and Bases - Online Tutor, Practice Problems & Exam Prep

Acids are substances that increase the concentration of hydrogen ions (H⁺) in a solution, while bases decrease this concentration. For example, hydrochloric acid (HCl) dissociates in water to release H⁺ ions, raising their concentration. Conversely, sodium hydroxide (NaOH) dissociates to produce hydroxide ions (OH^-), which react with H⁺ ions to form water, thus lowering their concentration. Understanding the behavior of acids and bases is crucial for many biological processes.

Acids and Bases

In this video, we're going to begin our lesson on acids and bases. You all need to know that many biological processes are influenced by the concentration of dissolved hydrogen ions, or [H⁺] ions, in the aqueous solution. The concentration of dissolved hydrogen ions can be abbreviated by brackets with an [H⁺] in the middle. Anytime you see brackets in science, it means the concentration of. What this bracket means is the concentration of hydrogen ions. Acids and bases are substances that directly affect the concentration of hydrogen ions. The concentration of hydrogen ions is really important because it will strongly affect many biological processes that we'll talk about later in our course. But in our next lesson video, we're going to talk more details about exactly how acids directly affect the hydrogen ion concentration. Then, later in a different video, we'll discuss how bases directly affect the hydrogen ion concentration. I'll see you all in our next lesson video to talk about acids.

Acids

In this video, we're going to introduce acids. Acids are any chemical that increases a solution's concentration of hydrogen ions or H⁺ ions. Recall that the concentration of hydrogen ions can be abbreviated with brackets like this, and it has H⁺ in the middle. Whenever we see brackets in science, it indicates the concentration of what's between the brackets. This is the concentration of hydrogen ions here. So acids will increase the concentration of hydrogen ions in solution.

If we look at the example below, at the addition of hydrochloric acid or HCl to water, we can see an example of an acid. Notice on the far left, we're showing four different molecules of hydrochloric acid or HCl, numbered 1, 2, 3, and 4. As the name implies, hydrochloric acid is an acid, which means that when added to water, it increases the concentration of hydrogen ions. When a hydrochloric acid molecule is added to water, it splits into two components: a hydrogen ion and a chloride anion. Each HCl molecule splits into H⁺ and Cl^- when added to pure water.

Notice over here in this beaker, there are these chloride anions, three out of four since we have four HCl molecules, and we also have four hydrogen ions. Through the addition of HCl to pure water, we have an increase in the concentration of hydrogen ions. We have more hydrogen ions in the solution than what we had before. So, we can say that we have increased the hydrogen ion concentration. That is it for acids. Acids are any substance that will increase the concentration of hydrogen ions. The concentration of hydrogen ions is very important for biological processes, and we'll learn more about that as we move forward in our course.

In our next video, we're going to talk about bases. I'll see you all there.

Bases

So now that we've introduced acids in our last lesson video, in this video we're going to introduce bases. Bases are pretty much the complete opposite of acids, and that's because instead of increasing the concentration of hydrogen ions, bases are any chemical that decreases a solution's concentration of hydrogen ions. Now a classic example of a base is Sodium Hydroxide or NaOH. If we look at our image below at the addition of Sodium Hydroxide (NaOH) to water, then we'll be able to see an example of a base. Notice over here on the far left, we're showing you three molecules of Sodium Hydroxide (NaOH), 1, 2, and 3. When each of these sodium hydroxide molecules is added to water, they will actually split into two substances. They will split into sodium ions (Na⁺) and hydroxide ions (OH^- ions). You can see that when we add these three sodium hydroxide molecules to water, the sodium hydroxide molecules are going to split into sodium ions and hydroxide ions.

Notice that even in some pure water over here, there's going to be a little bit of hydrogen ions (H⁺) floating around, so you can see that we start with three hydrogen ions. It's important to note that each of these hydrogen ions that we see here will actually interact with the hydroxide ions. When the hydrogen ions interact with the hydroxide ions, it creates water molecules. You can see that the H⁺ ions are now being decreased. Over here in the last beaker, because once again all of the OH^- ions interact with the H⁺ ions to form water molecules, notice that in this final beaker on the right, the concentration of hydrogen ions has indeed been decreased. Unlike acids, which result in an increased hydrogen ion concentration, bases result in a decreased hydrogen ion concentration, just as we see here.

This concludes our introduction to bases, and we'll be able to get some practice as we move forward in our course. I'll see you all in our next video.

Which of the following reactions is most consistent with that of a base?

a) NH₄⁺ → NH₃ + H⁺

b) H₂CO₃ → HCO₃^- + H⁺

c) NaOH → Na⁺ + OH^-

d) HCl → H⁺ + Cl^-

• A. a) NH₄⁺ → NH₃ + H⁺
• B. b) H₂CO₃ → HCO₃^- + H⁺
• C. c) NaOH → Na⁺ + OH^-
• D. d) HCl → H⁺ + Cl^-

The addition of an acid like HCl to an aqueous solution (pure water) would result in:

a) An increase in pH only.

b) Both the release of H⁺ and an increase in pH.

c) Both the release of H⁺ and a decrease in pH.

d) The release of H⁺ into the solution only.

e) A decrease in pH only.

• A. An increase in pH only.
• B. Both the release of H​⁺​ and an increase in pH.
• C. Both the release of H⁺ and a decrease in pH.
• D. The release of H⁺ into the solution only.
• E. A decrease in pH only.

In what way(s) do bases work to increase the pH of a solution?

a) Increasing the concentration of hydroxide ions.

b) Decreasing the concentration of hydrogen ions.

c) Decreasing the concentration of hydroxide ions.

d) Increasing the concentration of hydrogen ions.

e) Both a & b.

f) Both c & d.

• A. Increasing the concentration of hydroxide ions.
• B. Decreasing the concentration of hydrogen ions.
• C. Decreasing the concentration of hydroxide ions.
• D. Increasing the concentration of hydrogen ions.
• E. Both a & b.
• F. Both c & d.

Here’s what students ask on this topic:

What is the difference between acids and bases?

Acids and bases are substances that affect the concentration of hydrogen ions (H⁺) in a solution. Acids increase the concentration of H⁺ ions, while bases decrease it. For example, hydrochloric acid (HCl) dissociates in water to release H⁺ ions, raising their concentration. Conversely, sodium hydroxide (NaOH) dissociates to produce hydroxide ions (OH^-), which react with H⁺ ions to form water, thus lowering their concentration. Understanding the behavior of acids and bases is crucial for many biological processes.

How do acids increase the concentration of hydrogen ions in a solution?

Acids increase the concentration of hydrogen ions (H⁺) in a solution by dissociating and releasing H⁺ ions. For instance, when hydrochloric acid (HCl) is added to water, it dissociates into H⁺ ions and chloride ions (Cl^-). This dissociation increases the number of free H⁺ ions in the solution, thereby raising the hydrogen ion concentration. This process is crucial for various biological reactions and processes.

What happens when sodium hydroxide (NaOH) is added to water?

When sodium hydroxide (NaOH) is added to water, it dissociates into sodium ions (Na⁺) and hydroxide ions (OH^-). The hydroxide ions (OH^-) then react with hydrogen ions (H⁺) present in the water to form water molecules (H₂O). This reaction decreases the concentration of hydrogen ions in the solution, making it more basic. This behavior is the opposite of acids, which increase the hydrogen ion concentration.

Why is the concentration of hydrogen ions important in biological processes?

The concentration of hydrogen ions (H⁺) is crucial in biological processes because it affects the pH of the environment, which in turn influences enzyme activity, protein structure, and cellular functions. Many biochemical reactions are pH-dependent, meaning they only occur efficiently within a specific pH range. Therefore, maintaining the proper balance of H⁺ ions is essential for the optimal functioning of biological systems.

Can you explain the dissociation of hydrochloric acid (HCl) in water?

When hydrochloric acid (HCl) is added to water, it dissociates into hydrogen ions (H⁺) and chloride ions (Cl^-). The dissociation can be represented by the equation:

${\mathrm{HCl}}_{}\to H_{}+{\mathrm{Cl}}_{}-$

This process increases the concentration of H⁺ ions in the solution, making it more acidic. The increased H⁺ ion concentration is a key characteristic of acids and is important for various biological and chemical reactions.