Bases Introduction - Online Tutor, Practice Problems & Exam Prep

Bases are substances that neutralize acids and can be categorized as ionic or covalent. Ionic bases consist of a metal cation paired with basic anions such as hydroxide (OH^-), hydride (H^-), amide (NH₂^-), and oxide (O^2-). Examples include lithium hydroxide (LiOH), calcium hydride (CaH₂), sodium amide (NaNH₂), and barium oxide (BaO). Covalent bases are neutral amines, composed of nitrogen and hydrogen or carbon, nitrogen, and hydrogen. When dissolved in water, bases ionize, releasing cations and basic anions. They are characterized by a bitter taste and slippery feel, akin to soap. Additionally, bases turn red litmus paper blue, indicating their basicity. Understanding these properties of bases, including their reactions and characteristics in aqueous solutions, is important in the study of acid-base chemistry.

Intro to Bases

Now a base is any substance that can neutralize an acid within a chemical reaction. Now here we're going to breakdown bases into either being ionic bases or covalent bases. For ionic bases, we're going to say these are ionic compounds containing a metal cation, so positive metal connected to a basic anion. Now the basic anions are hydroxide ions, hydride ions, amide ions, and oxide ions.

So what do they look like? Well, hydroxide is OH-. Hydride is H- and amide is NH2-. Now pay close attention to mine is made-up of nitrogen, hydrogen. So it's it's an amine and it's negatively charged and then oxide is O2-. We said that ionic ionic bases basically have these basic ions, anions connected to a metal cation. So let's put here lithium ion, Let's put here calcium ion here, let's do sodium ion and let's do barium ion here.

So here. Remember, when the numbers and the charges are the same, they just simply cancel out and then we just have LiOH. So this is lithium hydroxide. In this one. The numbers are different within the charges, so they crisscross. Remember, you only crisscross the numbers. Don't worry about the charges. So this would be calcium hydride. Here the numbers are the same, they cancel out. So this would be sodium amide. And then both the numbers are the same, they cancel out. So this would be barium oxide. Some examples of typical ionic bases.

Now here, covalent bases, we're going to say this is restricted to our neutral amines. Remember, what is an amine? These are compounds composed of just nitrogen and hydrogen or carbon, nitrogen and hydrogen. So just remember, when we look at a base, we can either look at it as an ionic base or a covalent base.

Bases Introduction Example

Which of the following represents the possible structure of a base? So remember bases can either be ionic bases or they can be covalent bases. For the first one we have C4H all right. So if we take a look at this, this would not be an ionic basin that doesn't have a metal cation involved, it's only non metals there. And it wouldn't be a neutral base either because it's not an amine. So this would not be an answer.

BB isn't a mean because it's composed of nitrogen and hydrogen. But remember, typically we're going to say the neutral means are what's going to be classified as a base. Positive means we've talked about before in earlier videos. Positive means are typically acidic, so this would not work.

C is an answer because in C we have potassium which is a metal connected to hydroxide ion. See it was K+ and OH- that combined to give us potassium hydroxide.

Then finally, D doesn't work because D is a covalent compound that begins with the hydrogen, which is a simple way of looking at this being an acid. Out of all the choices only options, C represents atypical base.

Characteristics of Bases

Now, like acids, bases share certain similar characteristics when placing aqueous solutions. Here, we're going to look at the dissolution of bases. We're going to look at taste and feel, and then we're going to look at litmus paper. So bases, just like acids, will ionize when placed in water.

So here we have an example of sodium hydride. Sodium breaks up into Na1+(aq), and then we have the hydride ion. Remember the hydride ion represents a basic anion and then here we have strontium hydroxide. Strontium is a group 2A, so it's Sr2+(aq) and then we have two hydroxide ions, OH2(aq) taste and feel.

We're going to say here that bases have a bitter taste. So a good way to remember is bases with B, bitter with B. And we're going to say they are slippery to the touch. Believe it or not, when we look at soap, soap represents a base. Soap. Just remember the way they taste. They are bitter and they are slippery to the touch. Think of soap as a way of of remembering how bases can be used in everyday use.

Now litmus paper, Remember, litmus paper reacts just in the same way as acids and can we can use litmus paper on acids, we can use litmus paper on bases. Now here though, the litmus paper reacts to the presence of the basic anion, here a base. We're going to say it changes a red litmus paper into blue. So you take your red limits paper, you dip it into the basic solution, and when you pull it out, the red litmus paper has transitioned to a bluish color. So keep these in mind when we're talking about the basic characteristics of a base.

Bases Introduction Example

Which of the following is a characteristic of a strong base? So here, when we look at these options, it doesn't matter if it's a strong base or a weak base. These are characteristics that are addictive of all bases. All right, so here it turns blue. Litmus paper red. Well, remember that happens not with bases, but with acids.

It releases H ions in a solution. No. When we talk about a base, it ionizes into a basic anion, which H⁺ is not. It removes OH^- ions in a solution. So here, if we had for example, lithium hydroxide, that would produce OH^-, it wouldn't remove OH^-. So this can't be true.

It can be used in production of cleaning supplies. Remember taste and feel. We said that basis taste bitter, but more importantly they feel slippery and we use an example of a bar of soap. That's because bases can be used within cleaning supplies. So here option D is the correct answer.

Which of the following compounds will turn a piece of red litmus paper to a bluish color? 

a) HI                                         b) C₆H₅NH₂                               c) CH₃COOH                            d) HOCN

• A. HI
• B. C₆H₅NH₂
• C. CH₃COOH
• D. HOCN

Here’s what students ask on this topic:

How does litmus paper identify a base?

Litmus paper is a simple indicator used to determine whether a substance is acidic or basic. When you dip a strip of litmus paper into a solution, the paper changes color due to a chemical reaction between the dye on the paper and the substance in the solution.

For a base (also known as an alkaline substance), litmus paper turns blue. This happens because litmus paper contains dyes derived from lichens that are sensitive to pH changes. In the presence of a base, the molecular structure of the dye changes, resulting in a color shift. If the substance is strongly basic, the change will be immediate and very noticeable. For weaker bases, the color change might be less pronounced, but it will still shift towards blue. Conversely, if the substance were acidic, the litmus paper would turn red. Neutral substances, with a pH of around 7, will not change the color of the paper.

How can a strong base be identified?

A strong base is a substance that can completely dissociate into its ions in an aqueous solution. This means that when a strong base is dissolved in water, it releases hydroxide ions (OH^-) readily, resulting in a high pH value, typically above 7. To identify a strong base, you can look for certain characteristics:

1. Chemical Composition: Strong bases often contain hydroxide ions. Examples include sodium hydroxide (NaOH), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)₂).
2. Reactivity: They readily react with acids in a neutralization reaction to form water and a salt. This reaction is usually vigorous and exothermic (releases heat).
3. Conductivity: In solution, strong bases are good conductors of electricity due to the high concentration of ions.
4. pH Level: Using pH indicators or a pH meter, a strong base will show a high pH, usually between 12 and 14.
5. Litmus Test: A strong base will turn red litmus paper blue, indicating its basic nature.

Remember, strong bases are corrosive and should be handled with care, using proper safety equipment like gloves and goggles.

How can a base be identified?

A base can be identified through several characteristics and tests. Chemically, bases are substances that can accept hydrogen ions (protons) or donate a pair of valence electrons to form a bond. Here are some common ways to identify a base:

1. pH Level: Bases have a pH greater than 7. Using pH paper or a pH meter can help determine the pH level of a solution.
2. Litmus Test: Bases turn red litmus paper blue, which is a quick and straightforward test.
3. Texture: Many bases feel slippery to the touch due to the saponification reaction with the fats on your skin.
4. Reaction with Acids: Bases react with acids to form salt and water in a neutralization reaction. This is often accompanied by a temperature change.
5. Conductivity: Aqueous solutions of bases conduct electricity because they contain ions.
6. Taste: Though not recommended as a test due to potential hazards, bases generally have a bitter taste.

Always handle bases with care, as they can be corrosive and harmful to skin and eyes. Use appropriate safety equipment when conducting tests involving bases.