Acids Introduction - Online Tutor, Practice Problems & Exam Prep

Common Acids

Hey everyone. So in our discussion of acids, recall acid themselves are covalent compounds that have a hydrogen ion connected to a nonmetal anion or a polyatomic ion. Remember, anion is just a negatively charged ion. We're going to say generally the hydrogen ion is at the beginning of the compound, except for cases such as acetic acid and positive amines.

And when we say amines, remember amines themselves are covalent compounds that are containing nitrogen and hydrogen or carbon, nitrogen and hydrogen. If we take a look here at some common types of acids we have HCl which is hydrochloric acid, H2S which is hydrosulfuric acid, HCN which is hydrocyanic acid. We have phosphoric acid and then if we look at the last three we can see in the first four their covalent compounds made-up of only nonmetals and they have hydrogen in the beginning so that the dead giveaway that we have an acid.

But in the final three we have acetic acid here. So remember acetic acid come away of writing it as CH3CO. Here the hydrogen is at the end. If it's written in this form we could also have it written in another form which you might see in that form. It follows the common setup of an acid where hydrogen is in the beginning followed by C2H3O2. So both of these ways are showing acetic acid.

And then in the last two we have positive amines. This one here is the ammonium ion. It is an ammonia because it is composed of nitrogen and hydrogen. It's an acid because it's a positively charged amine. And then over here we have methyl ammonium ion. It is also an amine because it's composed of carbon, nitrogen, and hydrogen. It is also acidic because it is positively charged.

Later on we'll talk about negatively charged and not charged amines. Just for now, remember that acids we if we have a positively charged amine, it constitutes an acid. All right. So just keep this in mind as general ideas when it comes to most types of acids that you'll see.

Acids Introduction Example

Which of the following does not represent the possible structure of an acid? So if we take a look at the first one, we have HBR. This is a covalent compound with hydrogen at the beginning. It represents hydrochromic acid, so this is not an answer.

The next one is also covalent compound with a hydrogen in the beginning, so that's a dead giveaway that we have an acid. This one here is called iotic acid and then we have C&D. If we look at these two options, D is an acid because it is a covalent compound with a hydrogen at the beginning. Here this is called hypochlorous acid.

The answer is option C. We have C&H together. We don't have the hydrogen in the front so and it's covalent, but it doesn't have the hydrogen in the front. We said there are a few exceptions where hydrogen may not be in the front of the covalent compound such as acetic acid and positively charged amines. Here chapter port doesn't constitute one of those exceptions, so this would not represent a typical type of acid. So in this question the answer is letter C.

Characteristics of Acids

Now we can say that acids belong to a distinct class of covalent compounds because of their characteristics in aqueous solutions. Now here we can take a look at the solution, taste reactivity and how acid react with litmus paper when it comes to dissolution. We're going to say that they ionize into hydrogen or hydronium ions. Hydrogen ions are H⁺. Hydronium ions are H₃O⁺. These two things are interchangeable. Later on when we go into further discussions of how acids react within aqueous environments, we'll see why that's true.

Now here we're going to say the ionize to hydrogen ion or hydronium ion, and an anion when dissolved in a solvent, typically water. So for example, here we have hydrochloric acid. When it dissolves into its ions, it gives us H⁺ (aq) + Cl^- (aq), and then here we have sulfuric acid. If we were to just completely ionize it, where it gives off all of its H⁺ ions, we'd have 2 H⁺ (aq) + our sulfate ion (aq). Later on, we'll see that this doesn't really happen. When it when you your acid has multiple H⁺ ions, they actually are lost within steps. Right now we're not going into that detail. Just realize that if we were to just remove all the H in this particular example, we'd have 2 H⁺ at the end.

Now here for taste, we're going to say the presence of H⁺ or H₃O⁺ ions give acids a sour taste. So if you want to think about sour, think of citrus fruit. We have lemons, we have oranges, they kind of have a sour taste to them. Now their reactivity we're going to say they react with metals to form H₂ gas. A very common type of experiment that some of you may have done in lab is the reaction between hydrochloric acid and magnesium solid. Here, when we do this, we produce hydrogen gas plus magnesium chloride (aq). Here, let's not worry about balancing the equation. Just realize that we create these two things as products.

And finally, litmus paper. We're going to say litmus paper is a type of paper that changes colors and responds to an acid or a base for an acid. It changes red litmus paper or it changes blue litmus paper into red. So we take our blue litmus paper, dip it within an acidic solution, and when we pull it out, the blue litmus paper has changed to red. These are some of the most important characteristics of a typical acid.

Acids Introduction Example

Here in this example question, it says sulfuric acid is added to a large container of water. How is the solution different from the original water? All right, so here the solution has fewer hydrogen ions. Now remember when we place sulfuric acid within our aqueous solution, it will produce H+ ions plus sulfate ions.

Again, this doesn't all happen in one in one step we'd lose each H+ ions within different steps. We'll talk about that much later on, but for right now, if we're going to lose all the H+ ions, we'd have two H+ ions within solution and then our sulfate ion and solution. So there should be more H+ ions within our solution, not fewer.

The solution turns blue litmus paper red, which is true. The solution turns red litmus paper blue no. And assets would change blue litmus paper into red. The solution has more water molecules. So here molecules would mean that it stays intact and it doesn't become ions. But we know that if we take sulfuric acid and place it within the water, we're going to produce these ions.

So there will be fewer molecules and more ions within our new solution. So here the only answer that's true is option B.

Which of the following is true in regards to HNO₃? 

a) It has a bitter taste.                                                                        b) It produces H⁺ ions in water.

c) It exists as only molecules when dissolved in H₂O.                    d) It decreases the acidity of the solution.

• A. It has a bitter taste.
• B. It produces H⁺ ions in water.
• C. It exists as only molecules when dissolved in H₂O.
• D. It decreases the acidity of the solution.