What is an Acid in Chemistry?
What is an acid? Acid is mostly taken by Arrhenius definition as a substance that dissolves in water to produce hydrogen ion as the only positive ion. This definition holds true in all cases though acid can be defined and explained using other different concepts..
However, I will talk about Acids, Bases, and Salts in Chemistry.
What are Acids, Bases, and Salts?
Chemical products can occur as an acid, base or salt due to their specific properties.
Theories of Definitions of an Acid
Arrhenius theory: An acid is a substance that produces hydrogen ion (H+) as the only positive ion when dissolved in water.
Bronsted-Lowry theory: An acid is a substance that donates a proton
Lewis theory: An acid is an electron-pair acceptor.
Acids could be mineral or organic. Organic or natural acids are acids gotten from plants and animals. They include methanoic acid from insect bites or bee stings, ethanoic acid from vinegar, lactic from sour milk etc
Inorganic acids or mineral acids are acids synthesized in the laboratories and they include sulphuric acid, nitric acid, hydrochloric acid, etc.
Facts about an Acid
- Acids have pH less than 7
- Basicity of acid is the number of replaceable hydrogen ion in one mole of an acid
- Most concentrated acids fumes
- Organic acids are generally weak acids
What are the properties of Acids?
Physical properties of Acids
- Concentrated forms of acids are corrosive
- Acids turn blue litmus paper red
- Acids have sour taste
Chemical properties of acids
There are three basic chemical properties of acids
- Acids react with metals: Metals react with acids to form salts and liberate hydrogen.
However, it is important to mention that only a few metals can do this without difficulty.
We call them the MAZIT metals; Magnesium, Aluminium, Zinc, Iron and Tin.
Mg + 2HCl –> MgCl2 + H2
Zn + 2HCl –> ZnCl2 + H2
Fe + H2SO4 –> FeSO4 + H2
Also, organic acids do this but the rate of reaction will not be as fast as the mineral acids?
To hasten the rate of a reaction a very strong metal could be used.
CH3COOH + Na –> CH3COONa + 2H2
CH3COOH + K –> CH3COOK + 2H2
2CH3COOH + Ca –> ( CH3COO)2Ca + 4H2
Why can’t other metals form salts and liberate hydrogen?
Very reactive metals and like sodium, potassium, and Calcium will lead to explosive reactions.
Less reactive metals like Gold, Silver, and Lead will not be able to displace hydrogen.
- Acids react with alkalis/bases to form salts: it is important to mention that there is a little difference alkali and a base.
An alkali is a base that is soluble in water. All alkalis are bases but not all bases are alkalis.
Alkalis react with acids to form salts. This reaction is called a Neutralization reaction.
HCl + KOH –> KCl + H2O
H2SO4 + NaOH –> Na2SO4 + H2O
CH3COOH + NaOH –>CH3COONa + H2O
- Acids react with carbonates: Acids reacts with carbonates to form salts, water and liberate carbon iv oxide.
This reaction is usually accompanied by fizzing or bubbling since gas is evolved.
HCl + CaCO3 –> CaCl2 + H2O + CO2
HCl + MgCO3 –> MgCl2 = H2O + CO2
H2SO4 + MgCO3 –> MgSO4 + H2O + CO2
Theories of the Definition of a Base
Just like the acid, there are definitions of a base that we need to learn.
Definition of a Base
Arrhenius theory: A base is a substance that produces hydroxide ion as the only negative when dissolved in water.
Bronsted-Lowry theory: A base is a substance that accepts a proton
Lewis theory: An acid is an electron-pair donor
What are the properties of a base?
A base or alkali has some unique properties that can be used to distinguish it from other substances.
Physical properties of a base
- Concentrated forms of alkalis and bases are corrosive
- They have bitter taste
- Alkalis change red litmus paper blue
Chemical properties of a base
- Base neutralizes an Acid : A base reacts with an acid in a reaction called neutralization .
NaOH + HNO3 –> NaNO3 + H2O
KOH +HCl –> KCl + H2O
- Bases react with ammonium salts to liberate ammonia: : Bases react with ammonium salt to liberate ammonia gas.
NaOH + NH4NO3 –>NaNO3 + H2O + NH3
KOH + NH4Cl –> KCl + H2O + NH3
Uses of bases
Differences between acids and bases
|Acids have a sour taste||Bases have a bitter taste|
|Acids change blue litmus paper red||Bases change red litmus paper blue|
What is salt in Chemistry?
A salt is a compound formed when the ionizable hydrogen ion from an acid has been partially or completely replaced by a metal or ammonium ion.
Types of salts
There are five types of salt and this depends on the reaction the acid and base react.
- Normal salts
- Acid salts
- Basic salts
- Double salts
- Complex salts
Normal salts are formed when all the replaceable hydrogen ions in the acid have been completely replaced by metallic or ammonium ions.
HCl + NaOH –> NaCl + H2O
H2SO4 + 2KOH –> K2SO4 + H2O
Acid salts are formed when the replaceable hydrogen ions in the acids are only partially replaced by a metal.
H2SO4 + NaOH –> NaHSO4 + H2O
H2SO4 + KOH –> KHSO4 + H2O
Also, acid salt is formed when a strong acid reacts with a weak base.
HCl + Ca(OH)2 à CaCl2 + H2O
Basic salts are formed when there is an insufficient supply of acid to neutralize the base.
Ca(OH)2 + HCl –> Ca(OH)Cl + H2O
Mg(OH)2 + HCl –> Mg(OH)Cl + H2O
Double salts are salts that contain more than one cation and anion. Alums and Tutton’s salts are double salts.
Alums have the general formula M1Miii(SO4)2-12H2O
Tutton’s salts have the general formula [MI]2M1(SO4)2.6H2O
Complex salts are salts formed by mixing two simple salts.
The properties of the complex salt are different from the properties of the two salts that make up the salt.
What are the uses of salts?
Preparation of salts
There are two factors considered in preparing salts.
- Solubility of salt in water
- Stability of salt to heat
Methods of preparing soluble salts
- By action of dilute acid and metal
Zn + 2HCl –> ZnCl2 + H2
- By action of dilute acid and alkali
HCl + NaOH –> NaCl + H2O
- By action of dilute acid and carbonates
2HCl + CaCO3 –> CaCl2 + H2O + CO2
Methods of preparing insoluble salts
- By double decomposition reaction
This reaction is otherwise called a precipitation reaction.
AgNO3 + NaCl –> AgCl + NaNO3
BaCl2 + K2SO4 –> BaSO4 + 2KCl
- By combination of constituent elements
Fe + S –> FeS
Fe + Cl2 –> FeCl2
Properties of salts
- Efflorescence : This is the ability of salts to lose part or all of their water of crystallization when exposed to the atmosphere.
Na2CO3.10H2O –> Na2CO3.H2O + 9H2O
- Deliquescence : This is the ability of a substance to absorb moisture from the atmosphere and form solutions.
sodium hydroxide, calcium chloride, silica gel, potassium hydroxide, iron III chloride
- Hygroscopy : Hygroscopy is the ability of a substance to absorb moisture from the atmosphere and becomes sticky or moist.
sodium trioxonitrate V, Copper II oxide, Quicklime
Common alts and their uses
|NaCl||Used in preserving food|
|MgSO4||Used as a laxative|
|Fused CaCl2||Used as a drying agent|
|CaCO3||Used to neutralize acidic soil|
|KNO3||Used in making matches and fertilizers|
In conclusion, acid, base, and salts are very essential in Chemistry and a proper understanding of what acid is would be great in your journey as a chemistry student. not only because of concept but uses.
A VERY GOOD SOURCE FOR CHEMISTRY INFOMATION.