Characteristics of acids and bases

The characteristics of acids and bases are all those properties and qualities with which we can distinguish between an acid and a base.

According to Arrehnius theory, an acid is a substance that releases H + protons when dissolved in water, and a base is any substance that releases OH  hydroxyl ions when in aqueous solution.

Ion formationHere I’mHere I’m
Neutralization reactionWhen it reacts with a base.When it reacts with an acid.
Water solubilitySolublePartially soluble. Calcium, barium and aluminum hydroxides are poorly soluble.
Electric conductivityHere I’mHere I’m
State of matterSolid, liquid or gaseousSolid, liquid or gaseous
Reaction with litmus paperRed coloringBlue coloring
pH valueUnder 7Greater than 7
Conjugate counterpartA weak acid forms a conjugate base.A weak base forms a conjugated acid.
Corrosive effectStrong acidsStrong bases

Characteristics of acids

Acids have several characteristics with which they can be identified.

Ability to form ions from acids

The main characteristic of acidic substances is that they can be ionized, that is, lose or gain electrons.

Hydrochloric acid HCl, a strong acid, ionizes to form Cl  chloride anion and H + proton .

Neutralization reaction

An acid reacts with a base to form a salt and water. This reaction is known as the neutralization reaction . For example, HCl reacts with NaOH to form sodium chloride NaCl (kitchen salt) and water:

Water solubility of acids

Acids are generally soluble in water. For example, hydrochloric acid or muriatic acid is moderately soluble in water, up to 82 g of HCl can be dissolved in 100 ml of water at 0ºC. In the case of sulfuric acid H 2 SO 4 , the mixture with water generates heat, so it is always advisable to add the acid to the water to avoid explosions.

Acid strength

How acids dissociate determines whether they are strong or weak. The strength of an acid is given by its dissociation constant .

Nitric acid HNO 3 is a strong acid because in aqueous solution it completely ionizes into protons and nitrate ions:

This means that when we add HNO 3 to water, when analyzing the water we will only find H + and nitrate ions, and practically no HNO 3 .

In contrast, the acetic acid found in vinegar is a weak acid , because only part of it dissociates:

That is why it is represented with arrows in two directions, this means that in aqueous solution we will have acetic acid, H + and acetate anion (H 3 C-COO  ) in equilibrium .

States of matter of acids

Acids can be found in a liquid, solid or gaseous state. For example, hydrochloric acid HCl is liquid, hydrogen sulfide HS is a gas, and oxalic acid is a solid.

Reaction with litmus paper from acids

When we place a strip of litmus paper in an acidic substance, the litmus paper turns red.

Identification of acids by their pH

PH is the measure of the amount of H + present in a solution. Thus, between pH 0 and 7, we are in the presence of an acid. For example, vinegar has a pH equal to 2, the pH of sulfuric acid in car batteries is equal to 1.

Electrical conductivity of acids

Because acids can dissociate and produce electrically charged ions, acidic solutions can conduct electricity. For example, inside car batteries, sulfuric acid, which is a strong acid, is used as a conductor of electricity.

Corrosive effect of strong acids

Strong acids have a corrosive effect, they can burn organic tissues so their handling must be extremely careful.

Weak acids form a conjugated counterpart

Weak acids when dissolved form what is known as a conjugate pair, that is, a weak acid forms a conjugate base.

For instance:

In this case, formic or methanoic acid (HCOOH), when dissociated, forms the conjugated base ion format.

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Characteristics of the bases

Next we present the properties of the bases or alkaline solutions that characterize them.

Base ionization capacity

Basic or alkaline substances are characterized by forming ions when dissolved in water:

In this case, the sodium hydroxide NaOH ionizes to form a hydroxide anion OH  and a sodium cation Na + .

A base reacts with an acid to form a salt

A base reacts with an acid in a neutralization reaction to form water and a salt, for example:

In this case, the aluminum hydroxide Al (OH) 3 , a base, reacts with the HCl and forms the aluminum chloride salt AlCl 3 and water. Aluminum hydroxide is used as an antacid to relieve gastric reflux by neutralizing the acid produced by the stomach.

Bases water solubility

Some bases are soluble in water. Alkaline earth hydroxides, such as calcium hydroxide and barium hydroxide, are poorly soluble in water. For example, sodium hydroxide or caustic soda can be dissolved 109 g in 100 ml of water at 20ºC. Whereas magnesium hydroxide or milk of magnesia Mg (OH) 2 is practically insoluble in water.

Strength of the bases

Depending on the degree of ionization of the base, these can be strong or weak. For example, lithium hydroxide is a strong base because in aqueous solution it completely ionizes into OH hydroxide ions and Li + lithium cations :

On the other hand, NH 3 ammonia is a weak base because when it comes into contact with water, not all the ammonia dissociates:

State of Matter of the Bases

Bases can be found in solid, liquid and gaseous states. For example, pure sodium hydroxide is solid, ammonia is a gas.

Reaction with the litmus paper of the bases

When we place a strip of litmus paper in an alkaline substance, the paper turns blue.

Identification of bases by their pH

The bases are characterized by having a pH between 7 and 14.

Electrical conductivity of the bases

The bases due to their ionization capacity are good conductors of electricity. For example, in alkaline batteries, potassium hydroxide KOH is used as the electrical conductor.

Corrosive effect of bases

Strong bases can damage organic tissues. For example, kitchen oven cleaners are generally strong bases, and it is always recommended to handle them with extreme care, wearing gloves and eye protection.

Weak bases form a conjugate counterpart

The weak bases when dissolved form a conjugated counterpart, that is, a weak base forms a conjugated acid.

For example, tris- (hydroxymethyl) amino methane (OHCH 2 ) 3 CNH 2 is a weak base whose conjugated acid is (OHCH 2 ) 3 CNH + :

This is the basis for the action of buffer substances or buffers , which are substances that are used to maintain the pH of solutions constantly.

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