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 acid-base balance is crucial for many biological processes, influencing pH levels and overall homeostasis.

Acids and Bases

In this video, we're going to begin our lesson on acids and bases. What you all need to know is that many biological processes are actually strongly affected 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 hydrogen ions.

Acids and bases are substances that directly affect the concentration of hydrogen ions. The concentration of hydrogen ions is really important because that will strongly affect many biological processes that we'll talk about later in our course. In our next lesson video, we are going to talk more about how acids directly affect the hydrogen ion concentration. 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 really just any chemical that increases a solution's concentration of hydrogen ions or H⁺ ions. And once again, recall that the concentration of hydrogen ions can be abbreviated with just brackets like this and an H⁺ in the middle. Because anytime we see the brackets in science, we know it means the concentration of what's between the brackets. So, this is the concentration of hydrogen ions here.

So acids will increase the concentration of hydrogen ions in solution. If we take a look at our example below at the addition of hydrochloric acid or HCl to water, we see an example of an acid. Notice over here on the far left, we're showing you four different molecules of hydrochloric acid or HCl, 1, 2, 3, and 4. As its name implies, hydrochloric acid is an acid, which means that when we add it to water, it will increase the concentration of hydrogen ions. What happens when we add a hydrochloric acid molecule to water? It will actually split up into two components.

It will split up into a hydrogen ion, and it will split up into a chloride anion. So the H⁺, and the Cl^-, is what each HCl molecule will split up into when we add it into pure water. Notice over here in this beaker, we have these chloride anions here, three out of four of them for that matter since we have four HCl molecules, and we also have four hydrogen ions. Ultimately, what we can see is that through the addition of HCl to pure water, at the end, due to the increase in the concentration of hydrogen ions, we have more hydrogen ions in the solution than what we had before.

And so, we can say that we have increased the hydrogen ion concentration. That is essentially it for acids. Acids are any substance that will increase the concentration of hydrogen ions. The concentration of hydrogen ions is highly important when it comes to biological processes, and we'll get to learn more about that as we move forward in our course.

But in our next video, we're going to talk about bases. So 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. That's because instead of increasing the concentration of hydrogen ions, bases are any chemical that decreases a solution's concentration of hydrogen ions. A classic example of a base is Sodium Hydroxide, or NaOH. If we take a look at our image down below at the addition of Sodium Hydroxide or 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 3 molecules of sodium hydroxide or NaOH, 1, 2, and 3. When each of these sodium hydroxide molecules is added to water, they will actually split into 2 substances: they will split into sodium ions and hydroxide ions. You can see that when we add these 3 sodium hydroxide molecules to water, the sodium hydroxide molecules are going to split into sodium ions and hydroxide ions. You'll notice that even in some pure water over here that there's going to be a little bit of hydrogen ions floating around, and so you can see that we start with 3 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 hydrogen ions are now being decreased. Over here in the last beaker, because once again all of the hydroxide ions interact with the hydrogen ions to form water molecules, notice that in this final beaker over here on the right, the concentration of hydrogen ions has indeed been decreased. Unlike acids, which result in increased hydrogen ion concentration, bases result in 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. So 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^-

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.

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.

Here’s what students ask on this topic:

What is the difference between acids and bases in terms of hydrogen ion concentration?

Acids and bases differ in how they affect the concentration of hydrogen ions (H⁺) in a solution. Acids are substances that increase the concentration of H⁺ ions. For example, hydrochloric acid (HCl) dissociates in water to release H⁺ ions, raising their concentration. In contrast, bases decrease the concentration of H⁺ ions. Sodium hydroxide (NaOH) dissociates in water to produce hydroxide ions (OH^-), which react with H⁺ ions to form water, thus lowering their concentration. Understanding this difference is crucial for many biological processes, as it influences pH levels and overall homeostasis.

How do acids affect biological processes?

Acids affect biological processes by altering the concentration of hydrogen ions (H⁺) in a solution. An increase in H⁺ ions can change the pH of the environment, which can influence enzyme activity, protein structure, and cellular functions. For instance, many enzymes have an optimal pH range and can become inactive if the pH deviates too much. Additionally, changes in pH can affect the ionization state of molecules, impacting their solubility and reactivity. Therefore, maintaining a proper acid-base balance is essential for the proper functioning of biological systems.

What happens when hydrochloric acid (HCl) is added to 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:

${\mathrm{HCl}}_{}(aq)\to H_{}(aq)+{\mathrm{Cl}}_{}(aq)$

This increases the concentration of H⁺ ions in the solution, making it more acidic. The increased H⁺ concentration can affect the pH of the solution and influence various biological processes that are sensitive to pH changes.

How do bases decrease the concentration of hydrogen ions in a solution?

Bases decrease the concentration of hydrogen ions (H⁺) in a solution by producing hydroxide ions (OH^-) that react with H⁺ ions to form water. For example, when sodium hydroxide (NaOH) is added to water, it dissociates into sodium ions (Na⁺) and hydroxide ions (OH^-). The hydroxide ions then react with hydrogen ions to form water, as shown in the equation:

${\mathrm{OH}}_{}(aq)+H_{}(aq)\to H_{}2O$

This reaction reduces the concentration of H⁺ ions, making the solution less acidic and more basic.

Why is understanding the acid-base balance important in biology?

Understanding the acid-base balance is crucial in biology because it affects the pH of biological fluids, which in turn influences many physiological processes. Enzyme activity, protein structure, and cellular functions are all pH-dependent. For example, enzymes have optimal pH ranges and can become inactive if the pH deviates too much. Additionally, pH changes can affect the ionization state of molecules, impacting their solubility and reactivity. Maintaining a proper acid-base balance is essential for homeostasis and the proper functioning of biological systems.