Acid-Base Introduction: Study with Video Lessons, Practice Problems & Examples

Acids are covalent compounds with a hydrogen ion connected to a nonmetal or polyatomic ion, typically ionizing in aqueous solutions to release H⁺ ions, resulting in a sour taste and a color change in litmus paper from blue to red. Bases, ionic compounds with metal cations and hydroxide ions (OH^-), ionize in water, producing a bitter taste and slippery feel, changing red litmus paper to blue. Understanding these properties is essential for grasping acid-base reactions and their applications in various chemical processes.

Acid-Base Introduction Concept 1

Now recall that acids are covalent compounds that have a hydrogen ion connected to a nonmetal anion, so a negative ion, or a polyatomic ion. Generally, the hydrogen ion is found at the beginning of the compound except for acetic acid. Here, we have examples of some common types of acids: hydrochloric acid, hydrosulfuric acid, hydrocyanic acid, phosphoric acid, and acetic acid. Remember, when we talked about acids, we said that acetic acid can be shown in a way where the hydrogen is not at the beginning, but at the end of the compound.

Acid-Base Introduction Example 1

Which of the following does not represent the possible structure of an acid? So remember, we said that generally speaking, when it comes to an acid, it's a covalent compound that has the hydrogen ion located at the beginning of the compound. The exception to this is acetic acid. If we take a look here, this is covalent with the hydrogen in the beginning, and that's because it's hydrobromic acid. Here we have a covalent compound with hydrogen in the beginning, so here this is iodic acid, and over here we have hypochlorous acid, a covalent compound with a hydrogen in the beginning. The answer is c. This is CH₄, also known as methane. It is not an acid. The hydrogen is not found in the beginning of this covalent compound, and by the definition we used earlier, it would not be classified as an acid. Now, there are other technicalities that make it not an acid, but just go by that simple definition.

Acid-Base Introduction Concept 2

Now, acids belong to a distinct class of covalent compounds because of their characteristics in aqueous solutions. Some characteristics of acids include dissolution, taste, reactivity, and how they react with litmus paper. For dissolution, acids ionize when placed in water. Here we have an example of hydrochloric acid. It would ionize in water, breaking up into its H+ ion, which is aqueous, plus the chloride ion, which is also aqueous. For sulfuric acid, there are 2 H+ in this compound, so it breaks up into 2 H+, aqueous, plus SO42-, aqueous. For taste, the presence of H+ ions gives acids a sour taste. You can see this in natural citrus fruits, such as lemons and oranges, which have a sour taste to them because of the natural acids found within them.

Regarding reactivity, acids react with metals to form H2 gas. A good example is hydrochloric acid reacting with magnesium solid. In this reaction, magnesium and chlorine react together to produce MgCl2, and then the hydrogen becomes H2 gas. Finally, concerning litmus paper, this is a type of paper that changes colors in response to an acid or a base. An acid will change blue litmus paper to red. When taking this blue litmus paper and dipping it into an acidic solution, to show that it's acidic, the litmus paper will change to red. These are some of the common types of characteristics that you'll find with different types of acids.

Which of the following compounds would produce the greatest concentration of hydrogen ions when dissolved?

• A. HNO₂
• B. HBrO
• C. H₃PO₄
• D. H₂SO₃

Acid-Base Introduction Concept 3

Generally speaking, we're going to say that bases represent ionic compounds containing a metal cation, so a positive metal ion, connected to the basic anion of hydroxide ion, which is OH^-. Now bases can also be represented by nitrogen-containing covalent compounds called amines. We'll talk about that later on, but these are the basic ideas when it comes to a base. So most common types of bases possess a metal connected to OH. So if you can spot that, that is a good indication that you have a base.

Acid-Base Introduction Example 3

It says, which of the following represents the possible structure of a base? So remember, the definition we went over was that most common types of bases possess a metal cation connected to the hydroxide ion. If we take a look here, we have a hydroxide ion in two places. Here's an OH and here's an OH. So b is out and d is out. In a, it's a carbon connected to OH. We said it's going to be a metal, so that would be out. Carbon is a nonmetal. Here the best structure for a base is c, potassium hydroxide. Potassium is a metal and OH is connected to it, so that represents a typical type of base.

Acid-Base Introduction Concept 4

Now, like acids, bases share in common certain characteristics when placed in aqueous solutions. Here we're going to take a look at their dissolution, their taste and feel, as well as their reaction with litmus paper. Just like acids, bases ionize when placed in water. Here we have sodium hydroxide. When I place it in water, it becomes sodium ion aqueous plus hydroxide ion aqueous. When I take strontium hydroxide and I place it in water, it becomes a strontium ion aqueous, plus 2 hydroxide ions aqueous. What about taste and feel? Well, we're going to say bases have a bitter taste. So bitter b base b. And they are slippery to the touch. A great example of a base is in the manufacture of soaps. Soaps can be slippery when they're wet. Now, litmus paper. Litmus paper reacts to the presence of the basic anion, the hydroxide ion. So, if I take red litmus paper and I dip it in a basic solution, it will change the red litmus paper to blue. Okay? So b base, blue, both of them have b. That's a great way to remember the color changes associated with the base. Just remember, these are the most basic characteristics of bases when you're discussing them in aqueous solution.

NaOH (s) → Na + (aq) + OH − (aq) Sr(OH) 2 (s) → Sr 2+ (aq) + 2 OH − (aq)

Acid-Base Introduction Example 4

It says, which of the following is a characteristic of a strong base? Alright. So it doesn't matter if it's a strong base or a weak base. These are characteristics of all bases:

• It turns blue litmus paper red. No. That wouldn't be a base. That would be an acid.
• It releases H⁺ ions in a solution. No. That would be also an acid. Acids release H⁺ ions.
• It removes H⁺ ions in a solution. We never talked about bases removing H⁺ ions from a solution.
• It can be used in the production of cleaning supplies. We said that bases can be used in the formation of soaps. Soaps are instruments to clean. Right? So, by extension, we can assume that bases can be used to make other cleaning supplies.

So here, the best answer would be option D.

Which of the following is true in regards to LiOH?

• A. It has a sour taste.
• B. It produces H⁺ ions in water
• C. It conducts an electrical current in solution.
• D. It decreases the OH^– ions in water.

Here’s what students ask on this topic:

What are the common characteristics of acids in aqueous solutions?

Acids in aqueous solutions exhibit several key characteristics. They ionize to release H⁺ ions, which contribute to their sour taste, commonly found in citrus fruits like lemons and oranges. Acids react with metals to produce hydrogen gas (H₂), and they change blue litmus paper to red. For example, hydrochloric acid (HCl) ionizes in water to form H⁺ and Cl^- ions. These properties are essential for understanding acid behavior in various chemical processes.

How do bases behave in aqueous solutions?

Bases in aqueous solutions ionize to release hydroxide ions (OH^-). They have a bitter taste and a slippery feel, similar to soap. Bases change red litmus paper to blue. For instance, sodium hydroxide (NaOH) ionizes in water to form Na⁺ and OH^- ions. These characteristics help identify bases and understand their role in chemical reactions.

What is the difference between acids and bases in terms of their ionization in water?

Acids ionize in water to release hydrogen ions (H⁺), while bases ionize to release hydroxide ions (OH^-). For example, hydrochloric acid (HCl) ionizes to form H⁺ and Cl^- ions, whereas sodium hydroxide (NaOH) ionizes to form Na⁺ and OH^- ions. This difference in ionization is fundamental to their distinct properties and reactions in aqueous solutions.

Why do acids taste sour and bases taste bitter?

Acids taste sour due to the presence of hydrogen ions (H⁺) in solution, which interact with taste receptors on the tongue. Common examples include the sour taste of citrus fruits like lemons and oranges. Bases taste bitter because of the hydroxide ions (OH^-) they release in solution. This bitter taste is often associated with substances like soap. Understanding these taste properties helps in identifying acids and bases in everyday life.

How do acids and bases affect litmus paper?

Acids and bases cause distinct color changes in litmus paper. Acids turn blue litmus paper red, indicating their acidic nature. For example, dipping blue litmus paper into hydrochloric acid (HCl) will turn it red. Conversely, bases turn red litmus paper blue, indicating their basic nature. For instance, dipping red litmus paper into sodium hydroxide (NaOH) will turn it blue. These color changes are useful for quickly identifying acidic and basic solutions.