Bronsted-Lowry Base: Definition & Examples

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  • 0:00 What Is A Bronsted-Lowry Base?
  • 2:10 Examples Of…
  • 5:05 Lesson Summary
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Lesson Transcript
Instructor: Nissa Garcia

Nissa has a masters degree in chemistry and has taught high school science and college level chemistry.

There are different definitions of bases from different scientists, so what classifies a solution as basic? In this lesson, we will learn about the definition of a basic solution proposed by two scientists, Bronsted and Lowry.

What Is a Bronsted-Lowry Base?

Back in 1923, two scientists, Johannes Nicolaus Bronsted and Thomas Martin Lowry published a theory on the behavior of acidic and basic solutions. Bronsted came from Denmark, and Lowry came from England. It was a great coincidence that they published the same theory independently but at the same time. That is why this theory, the Bronsted-Lowry definition of acids and bases, was named after the two of them.

For this lesson, we will be focusing on basic solutions and how they behave, according to Bronsted and Lowry. We refer to these solutions as Bronsted-Lowry bases. A Bronsted-Lowry base is a solution that behaves as a proton acceptor, and these protons are in the form of a hydrogen (H+) ion. The solution that behaves as a proton donor is called a Bronsted-Lowry acid. In general, this is the interaction between Bronsted-Lowry acids and bases:

A Bronsted-Lowry Base is a Proton Acceptor

We can see that when the Bronsted-Lowry 'accepts' the hydrogen (H+) ion coming from the acid, the hydrogen (H+) ion attaches itself to the Bronsted-Lowry base. The proton (H+ ion) has a charge of positive one, so when the base (B) accepts the proton, its charge increases by positive one (HB+). Since the acid (HA) lost or donated a proton, its charge decreases by one, and in this case, it results in a negative charge (A-). The arrow going forward and backward at the same time is an equilibrium sign, which tells us that the reaction can either go forward or backward.

Let's take a close look again at the Bronsted-Lowry acid-base reaction. We can see that when an acid donates a proton, the resulting product is a conjugate base. When the base accepts a proton, the resulting product that is formed is a conjugate acid. When we think of the meaning of the word 'conjugate', it means 'joined together' or 'coupled'. In the same way, an acid/base and its resulting conjugate base/acid are what we call conjugate acid-base pairs.

Conjugate Acid-Base Pairs

Examples of Bronsted-Lowry Reactions

What is the telltale sign that a substance is a Bronsted-Lowry base in chemical reactions? To find the answer, we look at which substance gains a hydrogen atom - the substance that gains a hydrogen atom is our Bronsted-Lowry base since it accepts protons in the form of hydrogen (H+) ions.

Here, let's take a look at some examples of Bronsted-Lowry acid-base interactions. We will practice identifying conjugate acid-base pairs and identifying which substances are Bronsted bases.

  • Example 1: Reaction between water and ammonia

Water and Ammonia Acid-Base Reaction

We can first identify the substances. Let's take a look at the following illustration below. Ammonia is the Bronsted-Lowry base because it is the 'proton acceptor' - it accepts a hydrogen atom from water. On the other hand, water is the Bronsted-Lowry acid because it is the 'proton donor'. The conjugate acid is the ammonium ion (NH sub 4+) because it is the substance produced after the proton, hydrogen, is accepted. The conjugate base is the hydroxide ion (OH-) because this is the substance produced when H2O donated the proton. The conjugate acid-base pairs are: H sub 2O/OH- and NH sub 3/NH sub 4+.

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