Acids, bases and salts

Jamaica Gleaner - - YL - FRANCINE TAY­LOR CAMP­BELL Con­trib­u­tor Francine Tay­lor-Camp­bell is an in­de­pen­dent con­trib­u­tor. Send ques­tions and com­ments to kerry-ann.hep­burn@glean­erjm.com

1. WHAT ARE THE CHEM­I­CAL RE­AC­TIONS OF ACIDS AND BASES?

Acids and bases dif­fer in the types of re­ac­tions they un­dergo and the prod­ucts formed. These re­ac­tions can be used to dis­tin­guish be­tween acids and bases.

2. HOW ARE SALTS FORMED?

Salts are sub­stances which con­tain a pos­i­tive ion from a metal (or am­mo­nium ion) and a neg­a­tive ion from a non-metal. Salts are usu­ally formed when acid reacts with a base or a car­bon­ate or metal. Salts can also be formed when an am­mo­nium salt is heated with an al­kali and when two sol­u­ble salts are mixed. The meth­ods used to ob­tain salts in­clude titra­tion, di­rect com­bi­na­tion and pre­cip­i­ta­tion. The type of method cho­sen de­pends on the sol­u­bil­ity of the salt. Sol­u­ble salts dis­solve in wa­ter (e.g., NaCl, KNO3), while in­sol­u­ble salts do not dis­solve in wa­ter (e.g., PbCl2, BaSO4).

A sol­u­ble salt is usu­ally pre­pared by re­act­ing the acid so­lu­tion with the base, metal or car­bon­ate. The so­lu­tion is heated to re­move excess wa­ter, fil­tered, then a small quan­tity of the fil­trate is left to evap­o­rate.

Crys­tals formed in this way usu­ally have their wa­ter of crys­tal­liza­tion and are termed hy­drated salts (e.g. CuSO4.5H2O). If they are heated to dry­ness and all the wa­ter of crys­tal­liza­tion is re­moved, the salts be­come an­hy­drous.

Hy­drated salts usu­ally change colour when the wa­ter of crys­tal­liza­tion is re­moved by heat­ing.

In­sol­u­ble salts are usu­ally pre­pared by mix­ing two so­lu­tions of sol­u­ble salts to­gether, then filtering, wash­ing and dry­ing the pre­cip­i­tate formed. This is also called a dou­ble de­com­po­si­tion re­ac­tion.

Ex­am­ple: lead ni­trate + sodium chlo­ride = lead chlo­ride + sodium ni­trate

The lead chlo­ride formed is the in­sol­u­ble salt, which would be seen as a pre­cip­i­tate.

Pb (NO3)2 (aq) + 2 NaCl (aq) = PbCl2 (s) + 2 NaNO (aq) 3

3. DIF­FER­EN­TI­ATE BE­TWEEN AN ACID SALT AND A NOR­MAL SALT

Salts can also be termed nor­mal or acid salts. If all the hy­dro­gen ions are re­placed in the acid, a nor­mal salt is formed. How­ever, if the hy­dro­gen ions were only par­tially re­placed, an acid salt is formed. Acid salts are formed from diba­sic and trib­a­sic acids.

Ex­am­ple: H2CO3 - Car­bonic acid is diba­sic (has 2 hy­dro­gen ions avail­able to be re­placed). If car­bonic acid reacts with sodium hy­drox­ide, two salts can be formed.

2 NaOH (aq) + H2CO3 (aq) Na2CO3 (aq) + 2 H2O (l) Nor­mal salt, sodium car­bon­ate, is formed.

NaOH (aq) + H2CO3 (aq) NaHCO3 (aq) + H2O (l) Acid salt, sodium hy­dro­gen car­bon­ate or sodium bi­car­bon­ate, is formed.

4. HOW ARE SALTS USED IN DAILY LIFE?

Salts are used in a va­ri­ety of ways, from sweet­en­ers to medicines and ad­di­tives and preser­va­tives in the food in­dus­try.

5. Cite some ap­pli­ca­tions of neu­tral­iza­tion re­ac­tions in ev­ery­day life.

Neu­tral­iza­tion re­ac­tions re­fer to re­ac­tions in­volv­ing acids and bases (car­bon­ates, etc).

COM­MON EX­AM­PLES OF NEU­TRAL­IZA­TION IN­CLUDE:

1. Adding lime (cal­cium ox­ide) to acidic soils to re­duce soil acid­ity.

2. Tak­ing antacids (in­di­ges­tion tablets) to treat acid in­di­ges­tion in the stom­ach.

3. Brush­ing with tooth­paste (ba­sic) to re­duce acid­ity in the mouth.

4. Acid rain dam­ag­ing car­bon­ate rocks, build­ings and met­als.

5. Us­ing bak­ing soda (ba­sic) to neu­tralise a bee st­ing (acidic).

6. Us­ing vine­gar (acidic) to neu­tralise a wasp st­ing (ba­sic).

Stu­dents from Mount Alver­nia High School in Mon­tego Bay, St James, get in­for­ma­tion on how to ap­ply to Bryant Univer­sity in Rhode Is­land, United States, from Claire Dun­ning (right), se­nior as­sis­tant di­rec­tor, in­ter­na­tional ad­mis­sions, Bryant Univer­sity, dur­ing day one of a two-day col­lege fair at The Ja­maica Pe­ga­sus ho­tel in New Kingston re­cently.

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