Danielle has taught middle school science and has a doctorate degree in Environmental Health
That scoop of baking soda you use when baking a cake, a household cleaner containing ammonia, and the bottle of antacid in your medicine cabinet all have something in common. Each of these products can be classified as a weak base. But what is a weak base anyway? Before we dive into a definition, let's first get a background on bases in general, and on one man whose discovery revolutionized the term.
Many, many, years ago (late 1900's), a chemist by the name of Svante Arrhenius changed the landscape of physical chemistry. He not only proposed the theory that dilute solutions could conduct electricity, but that acids, bases, and salts could break apart and form ions in a solution. This theory, along with other scientific theories, revolutionized the concept of how certain molecules (charged and non-charged) behave in a solution. It paved the way for our current understanding on a topic we will be discussing, weak bases.
There are three broad ways to define a base. The first one is an Arrhenius base. Named after the man Svante himself, an Arrhenius base is a base that breaks apart (dissociates) in solution, forming hydroxide (OH) ions. The second definition is a Bronsted Lowry base. This defines a base that is willing to accept protons in a solution. Finally we have a Lewis base. A Lewis base states that a base is an electron pair donor in solution.
With three different definitions, you may be wondering how any of them are related to a weak base. Well, we know that Arrhenius theorized that substances in dilute solutions can conduct electricity. This led to the creation of a term called an electrolyte. An electrolyte is a substance that forms ions (charged molecules) in a solution. Bases are a type of electrolyte.
Arrhenius knew that electrolytes (i.e. bases) will dissociate (or break apart) into ions in a solution. However, a problem appeared when it was discovered that some of these guys don't completely follow this theory. Some electrolytes (i.e. bases) dissociate 100% to form ions in solution (diagram 1a), while others dissociate only partially (diagram 1b). This partial dissociation leads us to our next point, the definition of a weak base.
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Weak bases are substances that do not fully dissociate into ions in solution. Weak bases can also be referred to as weak electrolytes. The illustration is diagram 1b shows you exactly how a weak base would behave in solution. As you can see, some of the weak bases in solution break apart (i.e. dissociate) into ions while others appear to have a tough time breaking apart.
Keep in mind that the full dissociation of a strong base is roughly 100%. To put things in perspective regarding weak base dissociation, it is roughly 5-10%. Just by looking at these numbers you can see there is a drastic difference between a strong base and weak base dissociating. Thus, it makes perfect sense why diagram 1a and 1b illustrates the difference in behavior between a strong base and weak base present in a solution. Let's look at a few examples of weak bases.
When we first started on this journey to learn about weak bases we discovered that baking soda, household ammonia cleaner, and even antacid pills are all weak bases. How is this so? Using what we already know about weak bases, and partial dissociation, we can apply this to an example using baking soda.
In diagram 2, you will see a mound of baking soda. If we take a magnifying lens and zoom into that baking soda, you will see numerous molecules called sodium bicarbonate. This compound is classified as a weak base. When you place sodium bicarbonate in water, it behaves just like a weak base. That is, it partially dissociates as some sodium bicarbonate molecules break apart into sodium and bicarbonate ions while other molecules do not. The good news is that this process of partial dissociation in water is applicable to the other examples of household ammonia and antacid pills. The only difference is the chemical compound being added to a solution.
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It can be as simple as wiping a window with a window cleaner (containing ammonia) or scooping out a teaspoon of baking soda to make your favorite chocolate chip cookies. Weak bases are found in a variety of everyday products such as these. Always remember -- weak bases are those substances that have a tough time dissociating in solution. Sometimes they behave in a manner that results in complete dissociation into ions. Other times they simply decide to be the rebel and refuse to follow the rules of complete acid/base dissociation.
Weak bases are a type of base that partially dissociates in solution. They are also referred to as weak electrolytes. While a strong base dissociates 100% in solution, weak bases dissociate roughly 5-10%. A base (weak or strong) can be defined as the following three types: Arrhenius, Bronsted Lowry, and a Lewis Base. Examples of weak bases include baking soda, ammonia, and antacid medicine.
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