Acids and Bases in the Laboratory
Some common acids that are found in laboratories are Hydrochloric acid (HCl), Sulphuric acid (H2SO4) and Nitric acid (HNO3). Some of the lesser used acids are Acetic acid (CH3COOH), Hydrofluoric acid (HF), Carbonic acid (H2CO3). Hydrofluoric acid is a highly corrosive acid and is used to etch glass. Some acids are found in nature, like citric acid in certain fruits. These acids are called ‘organic acids’.
- Citric acid (from citrus fruits and vegetables,)
- Ascorbic acid (vitamin C, as from certain fruits)
- Acetic acid (Vinegar)
- Lactic acid (in buttermilk)
- Tartaric acid (Tamarind)
- Oxalic acid (Tomatoes)
Commonly found bases in laboratories and in our daily life are: Caustic soda, NaOH; Caustic potash, KOH; Milk of magnesia, Mg(OH)2; Liquor ammonia, NH3; Washing powder, Tooth paste.
One can familiarize with the acid base nature of some of the common substances by using litmus solution.
Make solutions of the following substances:
‘Borax’, ‘Blood’, ‘Milk’, ‘caustic soda’, ‘Lemon Juice’, ‘Bleaching powder’, ‘Tomatoes’, ‘Vinegar’, ‘detergent’, ‘Pure
Water’, ‘Coffee’, Baking Soda’.
Put a drop of each of the above solutions on a watch-glass and test by adding a drop of litmus to it.
Lemon juice, vinegar, tomatoes, coffee and milk turn litmus colour red indicating the acidic nature of these substances.
Pure Water does not show any change in colour of the litmus indicating its neutral character.
Blood, baking soda, borax, detergent, household ammonia, bleaching powder, caustic soda turn litmus colour blue showing the basic nature of these substances.
How do Acids React with Metals ?
Let us do more activities to understand the chemical nature of acids and bases.
Action on Metals :
Let us look at the way acids react with metals.
a) All metals above hydrogen in the metal reactivity series generally react with dilute acids to form their respective salt and liberate hydrogen.
Metal + Acid Salt + Hydrogen
b) Very active metals like potassium, sodium and calcium also react similarly, but tend to explode when combining with acids.
c) Nitric acid (of various concentrations) usually exhibits oxidizing property, rather than acidic properties. Metals such as magnesium combine with extremely dilute (1%) nitric acid to liberate hydrogen.
How do Metal Carbonates and Metal Hydrogen Carbonates React with Acids?
Acids react with carbonates and hydrogen carbonates (bicarbonates) to form their respective salt, water and carbon dioxide.
Carbonate/Bicarbonate + Acid Salt + Water + Carbon dioxide
How do Acids and Bases React with Each Other?
Acids and bases are the chemical ‘opposites’ of each other and the action of an acid and a base nullifies the effect of one on the
other. This is known as a neutralization reaction.
Neutralization : In a neutralization reaction an acid combines with a base, neutralizing the power of acid with a base and forms a molecule of water and the respective salt.
In general, a neutralization reaction can be written as:
Base + Acid ® Salt + Water
Reaction of Metallic Oxides with Acids
Action with Basic Oxides : Oxides that can add on hydroxyl ions (OH–) to their molecules are called basic oxides. These oxides get neutralized when they react with acids.
Basic oxide + Acid Salt + Water
Action with Basic Hydroxides : Acids undergo neutralization reaction with basic hydroxides to form salt and water.
Basic hydroxide + Acid Salt + Water
Reaction of Non-metallic Salts with Base : Calcium hydroxide, which is a base, reacts with carbon dioxide to produce a salt
and water. Since this is similar to the reaction between a base and an acid, we can conclude that nonmetallic oxides are acidic
Action of Alkalis/Base with Ammonium Salts : Alkalis combine with ammonium salts to liberate ammonia.
Alkali + Ammonium salt Salt + Water + Ammonia
CHEMICAL PROPERTIES OF ACIDS
|An acid when reacts with a base, salt & water are produced. This reaction is called neutralization|
HCl + NaOH èNaCl + H2O
HNO3 + NaOHè NaNO3 + H2O
HCl + KOHè KCl + H2O
REACTION WITH CARBONATES
|Acid and carbonates are combined to produce salt, water and carbon dioxide|
|MgCO3 + 2HCl è MgCl2 + CO2 + H2O
CaCO3 + 2HCl è CaCl2 + CO2 + H2O
Na2CO3 + H2SO4 è Na2SO4 + CO2 + H2O
CaCO3 + H2SO4 è CaSO4 + CO2 + H2O
REACTION WITH BICARBONATES
|Acid and bicarbonates are combined to produce salt, water and carbon dioxide|
NaHCO3 + HCl è NaCl + CO2 + H2O
REACTION WITH METAL
Zn + 2HCl è ZnCl2 + H2
2Al + 6HCl è 2AlCl3 + 3H2
|Reaction with iron oxide:|
6HCl + Fe2O3 è 2FeCl3 + 3H2O