acids and bases
- What are acids and bases?
- Characteristics of acids and bases
- Acids and bases in everyday life
- Acid and Base Indicators
- Neutralization reaction
- Examples of acids and bases
We explain what acids and bases are, their characteristics, indicators and examples. Also, what is the neutralization reaction.
Substances with a pH less than 7 are acidic and those with a pH greater than 7 are bases.
What are acids and bases?
However, there are two fundamental theories to explain what acids and bases are: the Arrhenius theory and the Brönsted-Lowry theory.
According to Arrhenius theory:
An acid is a substance that gives up protons (H +) in aqueous solution. That is, it is a neutral substance, which when dissolved in water dissociates into its ions according to the following reaction representative:
For example: hydrochloric acid (HCl)
A base is a substance that gives up OH– ions in aqueous solution. For example: sodium hydroxide (NaOH)
This theory has its limitations, because according to it these compounds are only defined in aqueous solution and not in other media. Furthermore, it does not explain compounds such as ammonia (NH3), which is a base, but since it does not have OH– in its composition, it does not meet the Arrhenius definition of base.
For all this, a new theory was needed to better explain the concepts of acid and base. So later Brönsted and Lowry developed a new theory, which includes Arrhenius principles but is not only thought of in aqueous solution, and therefore much more comprehensive.
According to the Brönsted-Lowry theory:
According to this theory, an acid is a chemical substance that is capable of giving up protons (H +) to another chemical substance and a base is that chemical substance that is capable of taking up protons (H +) from another chemical substance.
According to this theory, an acid-base reaction is an equilibrium that can be expressed as:
Where HA behaves like acid, since it gives up a proton H + to remain as A–. On the other hand, B behaves like a base, as it captures a proton H + to become HB +.
Some substances can behave as acids and bases at the same time and are said to be amphoteric. This depends on the environment in which they are or with whom they react. An example of this type of substance is water:
In the first equation, the water captures a proton H +, behaving like a base and becoming H3O +. While in the equation, water gives up a proton H +, behaving like an acid and becoming OH–.
Apparently in both theories, acids and bases have different proportions of hydrogen ions (H +). This determines its acidity (in the case of acids) or its alkalinity or basicity (in the case of bases).
The pH is the magnitude used to measure the acidity or alkalinity of a solution, that is, it indicates the concentration of hydrogen ions present in it.
- Acids. Substances with a pH of 0 to 6.
- Neutral Substance with pH 7 (water).
- Bases / alkalis. Substances with a pH of 8 to 14.
The lower the pH of a substance, the higher its degree of acidity. For example, pure HCl has a pH close to 0. On the other hand, the higher the pH of a substance, the greater its degree of alkalinity. For example, caustic soda has a pH equal to 14.
Characteristics of acids and bases
The difference in pH is the most noticeable feature of each one. When the pH value of a compound reaches one of its extremes, it means that this compound is highly dangerous for most matter, both organic, What inorganic.
Acids and bases have different physical characteristics:
- They have a sour taste (for example: acid present in various citrus fruits).
- They are highly corrosive and can cause chemical burns to the skin or respiratory damage if their gases are inhaled.
- They are good conductors of the electricity in aqueous solutions.
- They react with metals producing salts and hydrogen.
- They react with metal oxides to form salt and Water.
- They have a characteristic bitter taste.
- They are good conductors of electricity in solutions watery.
- They are irritants to the skin: they dissolve skin fat and can destroy organic matter due to their caustic effect. His breathing it is also dangerous.
- They have a soapy touch.
- They are soluble in water.
Acids and bases in everyday life
Battery acid creates a salt by reacting with metals.
The presence of acids and bases in our daily life is abundant. For example, inside the batteries of our electronic devices there are usually sulfuric acid. For this reason, when they are damaged and their contents are poured into the apparatus, they react with the metal of the electrodes and create a whitish salt.
There are also mild acids that we handle on a daily basis, such as acetic acid (vinegar), acetylsalicylic acid (aspirin), ascorbic acid (vitamin C), carbonic acid (present in carbonated sodas), citric acid (present in citrus fruits), or hydrochloric acid (gastric juice that our stomach secretes to dissolve food).
As for the bases, sodium bicarbonate is used for baking, as a deodorant and in various remedies against heartburn. Other commonly used bases are sodium carbonate (detergent), sodium hypochlorite (cleaning bleach), magnesium hydroxide (laxative) and calcium hydroxide (building lime).
Acid and Base Indicators
The way to distinguish between an acidic compound and a basic one is by measuring its pH value. Today there are numerous methods to measure the pH of a substance.
- Using acid-base indicators. Indicators are compounds that change from color by changing the pH of the solution in which they are found. For example, phenolphthalein is a liquid that turns pink if added to a base and turns colorless if added to an acid. Another example is litmus paper, which is immersed in a solution and if it turns red or orange it will be an acidic substance and if it turns dark it will be a basic solution.
- Using a potentiometer or pH meter. There are electronic equipment that directly give us the pH value of a solution.
The neutralization reaction or (acid-base reaction) is a chemical reaction What happens when these two types of compounds are mixed, obtaining in return a salt and a certain amount of water. These reactions are usually exothermic (they generate heat) and its name comes from the fact that the acid and base properties cancel each other out.
To classify neutralization reactions, it is important to know the types of acids and bases.
- Strong acid. It is an acid that when in aqueous solution is completely ionized, that is, it is completely transformed into ions that make up its molecule. For example: HCl (aq), HBr (aq), H2SO4 (aq).
- Strong base. It is a base that when in aqueous solution is completely ionized, that is, it is completely transformed into the ions that make up its molecule. For example: NaOH (aq), LiOH (aq), KOH (aq).
- Weak acid. It is an acid that when in aqueous solution is partially ionized, that is, it is not completely transformed into the ions that make up its molecule. Therefore, the ion concentration in solution of this type of acid is lower than in a strong one. For example: citric acid, carbonic acid (H2CO3)
- Weak base. It is a base that when in aqueous solution is partially ionized. That is, it is NOT completely transformed into the ions that make up its molecule. Therefore, the ion concentration in solution of this type of base is lower than in a strong one. For example: ammonia (NH3), ammonium hydroxide (NH4OH)
Neutralization reactions can occur in four ways, depending on the properties of their reagents:
- A strong acid and a strong base. The most abundant reagent will remain in solution with respect to the other. The pH of the resulting solution will depend on which reagent is in greater proportion.
- A weak acid and a strong base. A solution of basic pH will be obtained, the base will remain in the solution.
- A strong acid and a weak base. The acid is neutralized and an acid proportion will remain in solution, depending on the degree of concentration of the acid. The pH of the resulting solution is acidic.
- A weak acid and a weak base. The result will be acidic or basic depending on the concentrations of your reagents.
Examples of acids and bases
- Hydrochloric acid (HCl)
- Sulfuric acid (H2SO4)
- Nitric acid (HNO3)
- Perchloric acid (HClO4)
- Formic acid (CH2O2)
- Bromic acid (HBrO3)
- Boric acid (H3BO3)
- Acetic acid (C2H4O2)
- Caustic soda (NaOH)
- Calcium hydroxide (Ca (OH) 2)
- Ammonia (NH3)
- Sodium bicarbonate (NaHCO3)
- Potassium hydroxide (KOH)
- Sodium hypochlorite (NaClO)
- Calcium fluoride (CaF2)
- Barium hydroxide (Ba [OH] 2)
- Iron (III) hydroxide (Fe [OH] 3)