What does a caustic solution neutralize?

The neutralization

The observation of the neutralization

In chemistry, neutralization is understood to mean the elimination of the (among other things) corrosive effects of acids or bases. If sodium hydroxide is added to hydrochloric acid, a point occurs after a certain time at which the acidic effect is canceled out by the added alkali. The basis of neutralization is based on the fact that the effects of an acid and a base do not add but cancel each other when mixed.

Thus, an acid can be used with a suitable amount of a base and a base can be used with a suitable amount of an acid neutralized become. The change in the color of the indicator indicates this.

Experiment 2 shows that the neutralization is an exothermic process. The heat generated during this reaction is called the heat of neutralization.




The explanation of neutralization

If acids and alkalis are combined, hydrated protons and hydroxide ions meet. In simplified terms, this process can be interpreted as follows: positively charged protons and negatively charged hydroxide ions attract each other due to their opposite charge and combine to form neutral water molecules. The hydroxide ion acts here as a base: it picks up a proton.


$ \ mathrm {H ^ {+} _ {(aq)} \ qquad + \ qquad OH ^ {-} _ {(aq)} \ quad \ longrightarrow \ quad H_ {2} O \ quad + \ 57.3 \ kJ} $


The process of water formation from hydrated protons and hydroxide ions is the essential chemical process in neutralization. Since it is exothermic, we also understand the occurrence of the heat of neutralization.

During the neutralization, the cause of the acidic or alkaline reaction (H.+(aq) and oh(aq)) showing indicators are canceled. In our experiment, the neutralized solution contains sodium ions and chloride ions in addition to the water and the indicator. These form solid sodium chloride on evaporation. The neutralization of hydrochloric acid and caustic soda can now be fully formulated:


$ \ mathrm {\ underbrace {Na ^ {+} _ {(aq)} + OH ^ {-} _ {(aq)}} _ {caustic soda} + \ underbrace {H ^ {+} _ {(aq)} + Cl ^ {-} _ {(aq)}} _ {hydrochloric acid} \ longrightarrow H_ {2} O + \ underbrace {Na ^ {+} _ {(aq)} + Cl ^ {-} _ {(aq) }} _ {dissolved \ sodium chloride}} $ + 57.3 kJ



Change in conductivity during neutralization

During the neutralization, there is a change in the electrical conductivity, because the H.+(aq) and oh(aq) disappear. If the salt formed is also sparingly or practically insoluble in water, the conductivity drops sharply, as in our experiment 3. The neutralization of sulfuric acid is dealt with in the next chapter.