The neutralization reaction: sodium hydroxide and hydrochloric acid

Col­or­less, trans­par­ent, a caus­tic liq­uid that fumes in the air. Max­i­mum con­cen­tra­tion at 20 °C is 38%, with a so­lu­tion den­si­ty of 1.19g/cm³. High­ly-con­cen­trat­ed acid caus­es se­vere burns if it en­coun­ters skin, mu­cous mem­branes or eyes, but is present in the hu­man stom­ach at a con­cen­tra­tion of around 0.5%.

Chem­i­cal prop­er­ties

A strong acid that re­acts with:

• met­als;
• met­al hy­drox­ides;
• met­al ox­ides;
• met­al salts;
• strong ox­i­diz­ers;
• am­mo­ni­um. An in­ter­ac­tion with sil­ver ni­trate serves as a qual­i­ta­tive re­ac­tion to test for hy­drochlo­ric acid and its salts.

Field of use:

• hy­dromet­al­lur­gy and elec­trotyp­ing;
• chem­i­cal in­dus­try;
• food in­dus­try as the food ad­di­tive E507;
• medicine – to treat low acid­i­ty in the stom­ach.

And so a Chemist de­cid­ed to rec­on­cile the two hos­tile fam­i­lies and mar­ry the lovers, to do ev­ery­thing to make sure that the “re­ac­tion of sodi­um hy­drox­ide with hy­drochlo­ric acid” pro­ceed­ed as planned. A phe­nolph­thalein in­di­ca­tor served as the brides­maid for the “acid” bride. As soon as the re­ac­tion with the hy­drox­ide took place, the col­or­less in­di­ca­tor crim­soned with de­light. De­spite the ag­gres­sion of the sodi­um hy­drox­ide and hy­drochlo­ric acid, the re­ac­tion was a won­der­ful one. And its equa­tion reads as fol­lows:

HCl + NaOH = NaCl + H₂O + Q

Hy­drochlo­ric acid and sodi­um hy­drox­ide in­ter­act, re­sult­ing in salt and a re­lease of heat.

As we can see, the re­sult of the in­ter­ac­tion of two high­ly ag­gres­sive com­pounds is ta­ble salt and wa­ter – com­pounds that are ul­ti­mate­ly harm­less, even ben­e­fi­cial, to hu­man be­ings. And thus the two war­ring fam­i­lies ceased their ag­gres­sions and made peace.

To as­sess the prod­ucts of the re­ac­tion prop­er­ly, let’s get in a rock­et and ven­ture into space. We’ll look at our plan­et from a dis­tance. It’s called the blue plan­et for good rea­son, as 71% of its sur­face is com­prised of seas and oceans. Al­though, to be fair, we should note that only 1% of this wa­ter is suit­able for con­sump­tion. And wa­ter is one of the prod­ucts of our re­ac­tion.

And now let’s vis­it the best of restau­rants – you de­cide which! Let’s pro­ceed into the kitchen and ask the chef what two in­gre­di­ents they couldn’t do with­out. And be­lieve us, they won’t say caviar, truf­fles, or parme­san, they’ll say salt and wa­ter, as with­out these in­gre­di­ents you can’t pre­pare a sin­gle dish. And in com­bi­na­tion, our re­ac­tion prod­ucts can be found at home in soup, brine, or salt wa­ter. And now let’s dive in even deep­er, ex­am­in­ing the re­ac­tion of sodi­um hy­drox­ide and hy­drochlo­ric acid in the clas­si­fi­ca­tion of chem­i­cal re­ac­tions.

De­ter­min­ing the type of chem­i­cal re­ac­tion of hy­drochlo­ric acid with sodi­um hy­drox­ide

1. By the num­ber and state of the re­ac­tants and prod­ucts, it is an ex­change re­ac­tion. In oth­er words, the num­ber of sub­stances en­ter­ing into the re­ac­tion is equal to the num­ber of sub­stances re­ceived as a re­sult of the re­ac­tion. An sim­ple ex­change of ions has tak­en place. To clar­i­fy, let’s write our re­ac­tion equa­tion in ion­ic form:

H⁺ + Cl⁻ + Na⁺ + OH⁻ = Na⁺+Cl⁻ + H₂O

In ac­cor­dance with our sto­ry, the bride and groom have ex­changed their per­son­al prop­er­ty: what’s mine is yours. Here you can find out more about this dowry.

2. By the type of in­ter­act­ing sub­stances, it is a neu­tral­iza­tion re­ac­tion.

H⁺ + OH⁻ = H₂O

3. By the phys­i­cal state of sub­stances, it is ho­moge­nous. The sub­stances en­ter­ing into the re­ac­tion are in an iden­ti­cal phys­i­cal state – an iden­ti­cal liq­uid state.

4. By the di­rec­tion of the course of the re­ac­tion, it is ir­re­versible. The re­ac­tion con­tin­ues till the very end, un­til the re­act­ing sub­stances are com­plete­ly con­sumed.

5. By ther­mal ef­fect, it is exother­mic. In oth­er words, the wed­ding cer­e­mo­ny took place in a warm, friend­ly, and lov­ing at­mos­phere. The re­ac­tion is ac­com­pa­nied by a ther­mal ef­fect, and the amount of heat re­leased is 57.3 kJ/mol.

6. The re­ac­tion is not an ox­i­da­tion-re­duc­tion re­ac­tion: the ox­i­da­tion states of the atoms did not change over the course of the re­ac­tion.

H⁺Cl⁻ + Na⁺O²⁻H⁺ = Na⁺Cl⁻ + H⁺ O²⁻

And thus, our love sto­ry has a hap­py end­ing: lovers from two hos­tile fam­i­lies have joined to­geth­er in uni­ty.