The equivalent mass of phosphoric acid \(\left(\mathrm{H}_{3} \mathrm{PO}_{4}\right)\) in the reaction, \(\mathrm{NaOH}+\mathrm{H}_{3} \mathrm{PO}_{4} \rightarrow \mathrm{NaH}_{2} \mathrm{PO}_{4}+\mathrm{H}_{2} \mathrm{O}\) is (a) 98 (b) 89 (c) 49 (d) 58

A chemical reaction is a process where substances, known as reactants, transform into different substances called products. The reactant in our exercise is phosphoric acid \(\mathrm{H}_{3}\mathrm{PO}_{4}\), which reacts with sodium hydroxide (NaOH) to produce sodium dihydrogen phosphate (NaH2PO4) and water (H2O).

During a chemical reaction, the atoms in the reactants rearrange themselves to create the products. It's crucial to understand that no new atoms are created or destroyed; they are simply reorganized. In our example, phosphoric acid gives up one of its hydrogen atoms to form water, while the remaining molecule binds with sodium to form a new substance.

Focusing on the hydrogen atoms allows us to determine the equivalent mass of phosphoric acid, which is a key concept in understanding the stoichiometry of reactions involving acids and bases.

Molar mass is a physical property defined as the mass of a given substance (chemical element or chemical compound) divided by its amount of substance. It is expressed in units of grams per mole \(g/mol\). To calculate the molar mass of a compound, one adds up the mass of each element in the compound, multiplied by the number of atoms of that element in the compound's formula.

For phosphoric acid \(\mathrm{H}_{3}\mathrm{PO}_{4}\), its molar mass is calculated by summing the molar masses of three hydrogen atoms, one phosphorus atom, and four oxygen atoms. The calculated molar mass turns out to be 98 g/mol, which forms the basis for further calculations, like determining the equivalent mass in a reaction.

A neutralization reaction is a type of chemical reaction in which an acid and a base react quantitatively with each other. In a simple neutralization process, an acid reacts with a base to form water and a salt. This is exactly what occurs in the reaction given in our exercise where sodium hydroxide, a base, reacts with the phosphoric acid to produce water and sodium dihydrogen phosphate, a salt.

In such a reaction, the hydrogen ions (H+) from the acid meet the hydroxide ions (OH−) from the base, creating water (H2O). It's essential to understand that the concept of equivalent mass in phosphoric acid comes into play here, as the number of hydrogen ions it donates dictates its equivalent mass in the reaction. In our specific reaction, phosphoric acid donates one hydrogen ion, hence its equivalent mass is calculated as the molar mass divided by the number of hydrogen ions replaced.