Chances are you don’t know the history of acid and bases. You think just because you haven’t had to know about them before or you have forgotten about them, then they simply don’t matter all that much. Understanding the history of scientific discovery changes the way you see the present. It offers you a glimpse into the inevitability of future advancements in our understanding. After this lesson not only will you know how acid and bases came to be understood but how to use that knowedge to make our lives 10x better.
Once upon a time, in the land of chemistry, there lived a group of chemical compounds called acids and bases. The acids were known for their sour taste 🍋 and the ability to dissolve metals, while the bases had a bitter taste and were known for their slippery feel. Fortunately the history of acid and bases has progressed significantly and we since know more about this chemical class.
The history of acid and bases:
- Lavoisier Theory
- Humphrey Davy’s theory
- Arrhenius theory of acid and bases
- Bronsted-Lowry Theory of Acids and Bases
- Lewis Theory of Acids and Bases
One day, a scientist named Svante Arrhenius discovered that acids produce hydrogen ions (H+) when dissolved in water🌊, while bases produce hydroxide ions (OH-). He called this the “Arrhenius Theory of Acids and Bases.”
Another scientist named Bronsted and Lowry came along and expanded upon Arrhenius’ theory by stating that an acid is a substance that donates protons (H+ ions), while a base is a substance that accepts protons. This became known as the “Bronsted-Lowry Theory of Acids and Bases.”
But wait, there’s more! Another scientist named Lewis came along and proposed that an acid is a substance that accepts a pair of electrons✨, while a base is a substance that donates a pair of electrons. This is known as the “Lewis Theory of Acids and Bases.”
Nowadays, all three theories are used to help us understand the properties and reactions of acids and bases. And while they may have different definitions, they all agree on one thing: acids and bases are important chemical compounds that play a vital role in many aspects of our lives, from the food we eat to the medicine 💊 we take. So next time you’re enjoying a delicious slice of lemon pie or using baking soda to clean your sink, remember the fascinating history of acids and bases!
History of acid and bases in depth:
Lavoisier Theory
- Acids contain oxygen
An honourable mention which is specific to the HSC syllabus
Lavoisier was a French chemist who is considered the “father of modern chemistry.” One of his most significant contributions was his theory of acids ⚗️.
Lavoisier proclaimed “acid contains oxygen” using the example of sulfuric acid, H2SO4.
Lavoisier’s theory also helped to explain why some substances, such as lemon juice, have a sour taste. According to his theory, the sour taste is caused by the high concentration of oxygen in the solution.
Overall, Lavoisier’s theory isn’t used anymore since it has been disproved but it paved the way for later iterations in the definition of acid and bases.
Humphrey Davy’s theory
- Acids contain protons
Humphrey Davies was a British chemist who developed a theory about the nature of acids. According to Davies, an acid is a substance that has the ability to donate protons, or hydrogen ions, to a solution.
This theory is based on the concept of electronegativity, which is the measure of how strongly an atom or molecule attracts electrons. According to this theory, an atom or molecule with a high electronegativity will be more likely to donate protons to a solution, making it an acid.
Davies also proposed that the strength of an acid depends on the stability of the proton that is being donated. If the proton is stable and hard to remove, the acid will be stronger. On the other hand, if the proton is easily removed, the acid will be weaker.
So, in short, Humphrey Davies’ theory of acids states that acids are substances that can donate protons to a solution, and the strength of an acid depends on the stability of the proton being donated. Understanding this concept is important in many areas of chemistry, including understanding the behaviour of acids and bases in solutions, and predicting the outcomes of chemical reactions involving acids.
Arrhenius theory of acid and bases
- Acids disassociate to release H+ when dissolved in water and bases disassociate to release OH-
Have you ever mixed vinegar and baking soda together and watched the bubbly reaction that occurs? If so, you were witnessing the Arrhenius theory of acids in action!
According to this theory, acids are substances that increase the concentration of hydrogen ions (H+) in a solution when dissolved in water. Baking soda, also known as sodium bicarbonate, is a base that releases hydroxide ions (OH-) into a solution when dissolved in water. When these two substances are mixed together, the hydrogen ions from the vinegar react with the hydroxide ions from the baking soda to form water and carbon dioxide gas, causing the bubbly reaction you observed.
But what makes a substance an acid or a base? It all comes down to the ions they release when dissolved in water. Acids release hydrogen ions and bases release hydroxide ions. These ions then interact with each other to form new compounds, like water and carbon dioxide in the vinegar and baking soda reaction.
So next time you mix together some vinegar and baking soda, think about the Arrhenius theory and the role of hydrogen and hydroxide ions in the reaction. And maybe grab some protective goggles – that bubbly reaction can get pretty wild!
Bronsted-Lowry Theory of Acids and Bases
- Acids are proton donors and bases are proton acceptors
- Conjugate acid-base pairs
The Bronsted-Lowry theory of acids and bases is a theory that explains how certain substances react with each other in water. It is based on the idea that an acid is a substance that donates a proton (a small, positively charged particle) to another substance, and a base is a substance that accepts a proton from another substance.
To understand this theory, we need to understand the concept of pH. pH is a measure of how acidic or basic a substance is. A substance with a low pH (below 7) is considered acidic, while a substance with a high pH (above 7) is considered basic. Water has a pH of 7, which is considered neutral.
So, according to the Bronsted-Lowry theory, an acid is a substance that donates a proton to water, making it more acidic. For example, hydrochloric acid (HCl) is a common acid that donates a proton to water, making it more acidic. On the other hand, a base is a substance that accepts a proton from water, making it more basic. For example, sodium hydroxide (NaOH) is a common base that accepts a proton from water, making it more basic.
This theory helps us understand how certain substances react with each other in water and how to predict their behavior. It also helps us understand how acids and bases can be used to neutralize each other. For example, if we mix hydrochloric acid (an acid) with sodium hydroxide (a base), the acid donates its proton to the base, and the base accepts it. This neutralizes the acid and base, creating water and salt (NaCl).
Conjugate acid-base pairs:
Imagine that you are at a party and you are talking to a group of people. One person, let’s call him John, is feeling a little bit down because he just got into a fight with his girlfriend. You decide to try and cheer him up by telling him a joke.
As you start telling the joke, you notice that John’s mood starts to improve. You realize that you are acting as a base for John because you are helping to neutralize his negative emotions. On the other hand, if someone else at the party, let’s call her Jane, was feeling overly excited and energetic, you might try to calm her down by acting as a conjugate acid. Just like an acid helps to balance out a base, you are helping to balance out Jane’s excess energy and bring her back to a more neutral state.
In chemistry, conjugate acid-base pairs work in a similar way. An acid is a substance that donates protons (positively charged particles) to a solution, while a base is a substance that accepts protons. When an acid and a base react, they neutralize each other, creating a neutral solution. The conjugate acid is the product that is formed when a base donates a proton, while the conjugate base is the product that is formed when an acid donates a proton.
So, just like how you were acting as a base to neutralize John’s negative emotions and a conjugate acid to calm down Jane’s excess energy, conjugate acid-base pairs in chemistry help to balance out and neutralize each other.
In conclusion, the Bronsted-Lowry theory of acids and bases helps us understand how certain substances react with each other in water, and how to predict their behavior. It also helps us understand how acids and bases can be used to neutralize each other, creating new substances in the process.
Lewis Theory of Acids and Bases
- Acids are electron acceptors and basses are electron donors
The Lewis Theory of Acids and Bases is a theory that explains how acids and bases behave and how they react with each other. According to this theory, an acid is a substance that can donate a pair of electrons to another molecule. A base is a substance that can accept a pair of electrons from another molecule.
Imagine that you have two people, Anna and Ben, who are standing on opposite sides of a room. Anna has a basket of apples and Ben has a basket of bananas. Anna is willing to give away one of her apples to anyone who wants it, while Ben is willing to give away one of his bananas to anyone who wants it.
Now, imagine that you are standing in the middle of the room with a basket of oranges. You have an orange that you are willing to give away to either Anna or Ben. If you give the orange to Anna, she will be happy to accept it because she is willing to give away one of her apples in return. This is like an acid donating a pair of electrons to the orange.
On the other hand, if you give the orange to Ben, he will be happy to accept it because he is willing to give away one of his bananas in return. This is like a base accepting a pair of electrons from the orange.
So, in this way, the Lewis Theory of Acids and Bases explains how acids and bases behave and how they react with each other. It helps us understand the ways in which different substances can interact and form chemical bonds, and it is an important concept in the field of chemistry.
Exam-style Questions
Question 1.
Explain the progression in our understanding of acid and bases. [4 marks]
Question 2.
Outline the limitations of the Arrhenius theory of acids and how this was overcome by the Bronsted-Lowry model [3 marks]
Question 3.
Compare and contrast the Bronsted-Lowry model and Arrhenius theory of acids and bases [4 marks]
Answers
Question 1.
The history of acid and bases:
- Lavoisier Theory: acids contain oxygen
- Humphrey Davy’s theory: Acids have protons
- Arrhenius theory of acid and bases: Acids dissociate to form hydrogen ions and bases dissociate to form hydroxide ions
- Bronsted-Lowry Theory of Acids and Bases: Acids are proton donors and bases are proton acceptors, Conjugate acid base pairs
- Lewis Theory of Acids and Bases: Acids are electron acceptors and bases are electron donors.
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History of acid and bases Reference
- global OUP
- Return to HSC Chemistry Textbook