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, enhancing acidity. Conversely, sodium hydroxide (NaOH) dissociates to produce hydroxide ions (OH^-), which react with H⁺ ions to form water, thus reducing acidity. Understanding the behavior of acids and bases is crucial for grasping their roles in biological processes and maintaining homeostasis in living systems.

Acids and Bases

In this video, we're going to begin our lesson on acids and bases. And so what you all need to know is 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 really just be abbreviated by brackets with an H+ in the middle. Anytime you see brackets in science, it means the concentration of. What these brackets mean is the concentration of hydrogen ions. Acids and bases are substances that directly affect the concentration of hydrogen ions. Once again, the concentration of hydrogen ions is really, really important because that 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 about exactly how acids directly affect the hydrogen ion concentration. And then later in a different video, we'll talk about 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: [H⁺]. Whenever we see the brackets in science, it means the concentration of what's between the brackets. So, this is the concentration of hydrogen ions. Acids will increase the concentration of hydrogen ions in solution.

Let's take a look at our example below: the addition of hydrochloric acid, or HCl, to water. Notice on the far left, we're showing you four different molecules of hydrochloric acid. As its name implies, hydrochloric acid is an acid, meaning 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. It splits into a hydrogen ion, and into a chloride anion; the H⁺ and Cl^-, respectively, from each HCl molecule when added into pure water.

In the beaker, we have these chloride anions, three of four of them, since we have four HCl molecules, and we also have four hydrogen ions. Ultimately, we can see that 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 we had before.

Acids are any substance that increases the concentration of hydrogen ions. The concentration of hydrogen ion is really important in 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. So, I'll see you all there.

Bases

So now that we've introduced acids in our previous lesson videos, in this video we're going to introduce bases. Bases are practically the opposite of acids, and that is because, instead of increasing a solution's hydrogen ion concentration, bases are any chemical that decreases a solution's hydrogen ion concentration or concentration of hydrogen ions. An example of a base is sodium hydroxide, whose chemical formula is NaOH.

If we take a look at our example image below, we'll be able to see an example of a base, specifically the addition of Sodium Hydroxide or NaOH to water. Notice on the left hand side over here what we're showing you are three different Sodium Hydroxide molecules, 1, 2, and 3. When each of these sodium hydroxide molecules is added to water, the sodium hydroxide is going to dissociate, or break apart, or ionize into these ions. For example, this Sodium Hydroxide molecule will break apart into a Sodium ion or Na⁺ and a hydroxide ion or OH^-. This is going to be true for each of these sodium hydroxide ions.

Notice upon the addition of the Sodium Hydroxide to the pure water, the ions are going to break apart. So, you'll see three hydroxide ions and three sodium ions. Now you'll notice that even in pure water over here we're showing you some hydrogen ions, and this is going to be true even for pure water there will be some hydrogen ions. This is because water has the ability to auto ionize, which is something that we'll get to talk more about later in our course. For now, notice that there are some hydrogen ions even in pure water, and so you can see those hydrogen ions over here as well.

What's important to note is that each of these hydroxide ions is going to interact with a hydrogen ion, And so you will see these interactions right here, and when the hydroxide interacts with the hydrogen ion, they create water molecules, as you see right here. What you'll notice is that the concentration of hydrogen ions is being decreased because of the addition of this sodium hydroxide. Whereas there were three hydrogen ions in the pure water in this beaker here, in the final beaker, notice that there are not any hydrogen ions being shown, and so what this is showing is the decreased hydrogen ion concentration.

Once again, when a chemical decreases a solution's concentration of hydrogen ions, that chemical is referred to as a base. So, sodium hydroxide is indeed a base. The concentration of hydrogen ions is incredibly relevant to living systems, and so any substance that can change the concentration of hydrogen ions is going to be relevant as well, and so bases are very important. This here concludes our brief introduction to bases, and we'll be able to get some practice applying these concepts as we move forward. 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^-

• 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 the hydrogen ion concentration. Understanding these concepts is crucial for grasping their roles in biological processes.

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

Acids increase the concentration of hydrogen ions (H⁺) in a solution. When an acid like hydrochloric acid (HCl) is added to water, it dissociates into H⁺ ions and chloride ions (Cl⁻). The increase in H⁺ ions raises the overall concentration of hydrogen ions in the solution. This change in concentration is significant because it can affect various biological processes and chemical reactions.

What happens when sodium hydroxide 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 then interact 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 NaOH a base. The reduction in H⁺ concentration is crucial for various biological and chemical processes.

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, cellular functions, and metabolic reactions. Enzymes, for example, have optimal pH ranges in which they function most efficiently. Deviations from this optimal pH can lead to decreased enzyme activity and disrupted cellular processes. Therefore, maintaining a stable H⁺ concentration is vital for the proper functioning of biological systems.

What is the role of hydrochloric acid in increasing hydrogen ion concentration?

Hydrochloric acid (HCl) plays a role in increasing hydrogen ion (H⁺) concentration by dissociating into H⁺ ions and chloride ions (Cl⁻) when added to water. This dissociation releases free H⁺ ions into the solution, thereby raising the overall concentration of hydrogen ions. This increase in H⁺ concentration is significant for various chemical reactions and biological processes, such as digestion in the stomach, where HCl helps break down food.