In chemistry, understanding the basic concept of acid and base is really important. The characteristic of acid and base is vital to know how they would react with other types of matter. By knowing its properties and reaction, we can avoid any possible hazard from acid or base reaction. One of the popular chemical reaction is the acid in the water reaction. This article will cover this type of reaction, including the explanation about the acid and base itself, acid reaction in water reaction.
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1. Arrhenius Theory
There’re some famous definitions of acid and base explained by some great minds. One of them is Svante Arrhenius. He discovered the theory of acid and base in the 1884. He found out that the slat like sodium chloride would dissociate in water and produced ion. His theory consists of following principles:
- acid produces ions of H+ water solution
- base produces ions of OH– ions in water solution
- his experiment requires water. So to determine the type of solution, it must be the water-type solution
- The experiment only uses the protic acids. This acid will create the hydrogen ions
- For base, he only uses the hydrogen base
So, based on arrhenius theory, acid is the substance which ionizes when it dissolves in the water solution. It will produce the hydrogen ion (H+). While the base is the substance which produces hydroxide ion (OH-) when it dissolves in the water solution. The example of acids are HCl, HCN, H2SO4. The reaction of acid, for example HCl solution, is explained as follow:
HCl(g) → H+ (aq) + Cl- (aq)
Above reaction occurs in the water. We can see that the HCl (in gas form) will release the hydrogen ion and negative ion. While the example of base reaction can be seen below:
NaOH(s) → Na+ (aq) + OH- (aq)
NaOH in solid form will create the hydroxide ion (OH-) and positive ion. The other examples of base are KOH, Ca(OH)2 and many more.
- Even though that Arrhenius gave the great theory about acid and base, his explanation has some flaws. The weakness of Arrhenius theory are as follow:
- This theory is only applicable to the reactions occurring in the water. His definition is based on the acid and base properties when they dissolve in the water
- This theory is not able to describe the event of acidic solution formation from the hydrogen that has the +1 oxidation number. The compound like HCl has the hydrogen with the oxidation number of +1. This compound will dissolve in water and create the acid solution. However, the substance like CH4 can not create the acidic solution even though it has the oxidation number of +1 in its hydrogen.
2. Bronsted Lowry Theory
After Arrhenius theory, Bronsted and Lowry conducted the research to determine the characteristic of acid and base. They concluded that acid and base reaction is the reaction which acid releases the proton and the base accepts the proton. This theory has some basic points like below:
- Acid is the proton donor (create the proton)
- Base is proton acceptor (get the proton)
- This theory uses the aqueous solution
- All bases except hydroxide are allowed
- The protic acid only is allowed
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3. Lewis Theory
After previous great definitions of acid and base substance, Gilbert Newton Lewis tried to present another perspective to define the acid and base. Differ from Bronster-Lowry theory which is related to the proton, lewis theory will deal with the electron pairs. His theory consists of following points:
- Acid is the electron pair acceptor
- Base is the electron pair donor
- The restrictive model which defines the acid and base
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4. Robert Boyle Theory
In 1661, the famous scientist named Robert Boyle released the characteristic of acid and base substance. He proposed some basic differences between these two substances. We can see their behavior without conducting the chemical test. Here’re some properties of acid based on Boyle:
- It tastes sour. The word acid itself comes from the Lation word of acere which means sour
- It is corrosive
- It will change the litmus from blue to red color
- Acid in water solution form is able to conduct electrical current. It’s called as electrolytes.
- It reacts with base to create the salt and water
- It is able to evolve hydrogen gas in the reaction with active metal like aluminum, alkali metal, alkaline metal, zinc and so on.
While the base possess some qualities as follow:
- It tastes bitter
- It has slippery property
- It will not change the litmus color. It’s able to change the red litmus to the blue color
- Base in its water solution can conduct electric current
- It reacts with acid to make salt and water
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pH and pOH
Knowing the pH and pOH are also essential to understand the properties of acid and basic. Both pH and pOH are vital values in terms of acid and base solutions. pH and pOH are the log base 10 of the hydrogen ion concetration or the hydroxide ion concentration. This concept was firstly created by the famous chemist named LeChatelier. The LeChatelier theory explains the condition where the addition of a product to a equilibrium system is able to shift the equilibrium to the reactants.
The acid and base can dissolve in the water and pres the water to dissociate. They are able to do this because the acid and base enhance the concentration level of one product of water self ionization which can be proton or hydroxide ion.
We use the value of pH and pOH to explain the acid and base solution in the water. In the pure water condition, the concentration of proton is same with the concentration of hydroxide anion. In this condition, it will have the pH of 7. The acid solution has the pH lower than 7. While the base solution has the pOH larger than 7. The formula to determine pH and pOH is as follow:
[tabs]
[tab title=”pH and pOH
pH = -log[H+]
pOH = -log[OH-]
where:
[H+][OH-] = 10^-14
pH + pOH = 14
[/tab]
[/tabs]
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Strong and Weak Acid – Base Reactions
Strong acid will have the different characteristic with the weak acid. The strong acid has the tendency to fully dissolve in the water solution. It will have the negative value of Ka. Ka itself is the equilibrium constant for the acid dissoleve reaction in the water. Every substance will have its own Ka value. The examples of strong acids are sulfuric acid (H2SO4), perchloric acid (HClO4), nitric acid (HN)3), hydrobromic acid (HBr), hydrochloric acid (HCl), hydroiodic acid (HI) and many more.
Differ from strong acid, the weak acid will partially dissolve in the water solution. Some popular examples of weak acid are hydrofluoric acid (HF), bicarbonate (HCO3), carbonic acid (H2CO3), ammonium (NH4+), ammonia (NH3), hydrogen sulfide (H2S) and some more.
The strong base will also fully dissolve in the water solution. While the weak type base will reach the equilibrium state in the water. The examples of strong bases are NaOH, LiOH, Ca(OH)2. While the examples of weak bases are NH3, HS-, CO3-2, SO4-2 and others.
Acid in Water Reactions Formula
Acid and water can not be easily mixed together. If you’re trying to mix the strong acidic like sulfuric acid and water, you need to know the risk. If you pour water to the acid, it can cause the laboratory accident. Acid like sulfuric acid can react greatly with the water. Acid in water reaction is often called as exothermic reaction. You can see the acid in water reaction as follows:
H2SO4 + H2O → H3O+ + HSO4-
In above reaction, we can see that the sulfuric acid will donate the hydrogen ion to produce the hydronium ion. The sulfuric acid will turn to be the HSO4-, which is the conjugate base of sulfuric acid.
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How to Mix Acid and Water Properly?
As we mentioned previously, the acid in water reaction possess the laboratory safety hazard. The proper way to mix acid with water is by adding the acid to the water. We know that acid can react strongly with the water in the exothermic reaction. This reaction means that it will release the heat. If the heat is high enough, it can possibly boil the water.
If you do pour acid to water, the water will not splash up as there will acid reaction in water. Since water is less dense than sulfuric acid, the reaction will sink in the water. It’s less possible for you to get hurt by doing this way. In contrast, if you add water to acid, the water has the possibility to boil. Sulfuric acid is more dense than the water so the exothermic reaction will happen on the top of the water. Then, it can possibly splash and touch your skin. Sulfuric acid contains high level of hazard to human, especially if it touches your skin.
However, if you accidentally touch or spill sulfuric acid on your skin, you have to wash it with running cold water directly. You also have to follow every rule in the laboratory when you’re performing chemical experiment. Acid in water reaction is just an example of chemical reaction which may contain hazard. You have to always remember to add the acid instead add the water. This is extremely important especially when you’re working with the strong acid. The strong acid will fully react with the water.
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