4.3 Acid Base Reactions

2. Acid – Base Titrations:

An acid reacts with a base to in aqueous medium to produce salt and water. This reaction is called Acid – Base reaction or Acid – Base Neutralization or just Double Displacement/Replacement Reaction. A brief summary regarding acids and bases will be covered later. More details will follow in the later chapters.

Example:

HCl(aq)   +  NaOH(aq)   ….>  NaCl(aq)    +   H₂O(l)    +    Heat

HCl(aq)   +  H₂O(l)    …..>   H₃O⁺(aq)    +    Cl^–(aq)

NaOH(aq)   + H₂O(l)  ……>   Na⁺(aq)     +    OH^–(aq)  +   H₂O(l)

The complete ionic chemical equation is:

H⁺(aq)  +  Cl^–(aq)  +   Na⁺(aq)  +  OH^–(aq)   …..>   Na⁺(aq)  +  Cl^–(aq)  +  H₂O(l)   +   Heat

The net ionic chemical equation is: [Cl^–(aq) and Na⁺(aq) spectator ions]

H⁺(aq)   +   OH^–(aq)   …..>   H₂O(l)  +  Heat

The driving force for the acid – base reaction or neutralization is the formation of water by the reaction of the protons H⁺ or correctly said the H₃O hydronium ions with hydroxide ions.

There are two types of acids according to their dissociation in water.

1. Strong acid: is an acid that dissociate completely in water
2. Weak acid: is an acid that dissociate partially in water

Strong acids are known to be 7:

Perchloric acid: HClO₄

Chloric acid: HClO₃

Hydrochloric acid: HCl

Hydroiodic acid: HI

Hydrobromic acid: HBr

Nitric acid: HNO₃

Sulfuric acid: H₂SO₄

All other acids inorganic and organic acids are considered to be weak.

Acetic Acid: CH₃COOH

Hydrofluoric acid: HF

Phosphoric acid: H₃PO₄

Oxalic acid: H₂C₂O₄

Carbonic acid: H₂CO₃

Fruits are very rich with weak acids:

Figure 4.18 Sources of Acids in Fruits

Weak acids are founds in Vegetables as well:

Reference: https://www.livestrong.com/article/260893-names-of-acids-in-fruits-vegetables-dairy-products/

Asparagus

Beans

Corn

Cucumbers

Garlic

Green beans

Greens (lettuce, kale, collards, spinach, etc.)

Onions

Peas

Pumpkins

Squash

There are two types of bases according to their dissociation in water.

1. Strong base: is a base that dissociate completely in water
2. Weak base: is a base that dissociate partially in water

Strong bases are known to be 2 types of group 1A and 2A in periodic table:

Sodium hydroxide: NaOH

Lithium hydroxide: LiOH

Potassium hydroxide: KOH

Cesium hydroxide:  CsOH

Magnesium hydroxide: Mg(OH)₂

Calcium hydroxide: Ca(OH)₂

Strontium Hydroxide: Sr(OH)₂

Barium Hydroxide: Ba(OH)₂

All other bases inorganic and organic bases are considered to be weak.

Ammonium hydroxide: NH₄OH

Iron-III-hydroxide: Fe(OH)₃

Titanium-II-hydroxide: Ti(OH)₂

Aluminum hydroxide: Al(OH)₃

Pyridine: C₅H₅N

Aniline: C₆H₅NH₂

All amines are considered as weak bases such as methyl amine CH₃NH₂ etc…

Fruits and nuts are very rich with weak bases:

Figure 4.19 Nuts and dry fruits

Reference: https://nuts.com/healthy-eating/alkaline-diet

Reference: https://www.livestrong.com/article/494847-nuts-alkaline-forming/

The acid – base neutralization as mentioned yields salt and water:

Examples:

Fe(OH)3(aq)     +   3 HNO3(aq)        …..>    Fe(NO3)3(aq)       + 3  H2O(l)   [water is produced as by product]

This type of reaction is considered neutralization reaction as well as double Replacement/Displacement Reaction.

C6H5NH2(aq)   +  HCl(aq)    …..>    C6H5NH3+ Cl- (s)

Aniline    + Hydrochloric acid    ……>  anilinium chloride   [No water is produced as by product]

This type of reaction is considered neutralization reaction as well as Combination Reaction.

The video below illustrates the acid – base neutralization in some details:

Acid Base Neutralization Reactions & Net Ionic Equations – Chemistry