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PROTON CHEMISTRY: ACIDS AND BASES 603

An Acid Is a Proton-donor.

The characteristic chemical reactions of acids are given as follows:

1. Acids react with metals such as sodium, that have a smaller

attraction for electrons than hydronium ions have, to give hydrogen

gas.

I

loses an electron 4-

2(H30)+, CI + Na —>- Na+, CI" + H2 + H2O

hydrochloric acid sodium sodium chloride hydrogen water

I

gains an electron t

This reaction is obviously an example of a displacement type of

electron transfer.

2. Acids react with ammonia, NH3.

(H30)+, CI- + NH3 —> (NH4)+, CI- + H2O

hydrochloric acid ammonia ammonium chloride water

In this reaction the hydronium ion,

to ammonia, NH3.

(HsO)^, gives up a proton, H+,

3. Acids react with bases. Bases are recognized by their characteristic

properties ; a base is a substance whose water solution feels slippery,

tastes bitter or alkaline, changes the color of indicators to a color different

from tJiat produced by acids, and neutralizes acids to form salts. Some

common bases are: the weak base, ammonium hydroxide, NH4OH, a

3 per cent solution of which is the ordinary household aqua ammonia;

the strong base, sodium hydroxide, NaOH, which is commonly known

as soda lye;

the strong base, potassium hydroxide, KOH, known as

potash lye; and the mild base, calcium hydroxide, Ca(0H)2, known as

hydrated lime, which is used in making mortar and plaster. Strong

bases, such as sodium hydroxide and potassium hydroxide, are called

alkalies, because they are prepared from hydroxides of the alkali metals.

In the reaction of hydrochloric acid with sodium hydroxide, it is

evident that the hydronium ion, (HsO)"^, gave up a proton, H+, to

the hydroxyl ion, (OH)-, to form water.

(H30)+, CI + Na+, (OH)- —>- 2 H2O + Na+, CI"

hydrochloric acid sodium hydroxide water sodium chloride

(acid) (base) (salt)

In the reactions of hydrochloric acid with ammonia and with sodium

hydroxide, the fundamental reaction was that in which hydronium

ions gave up protons to another substance.

Inasmuch as this property of giving up protons to other substances

is characteristic of acids only, acids are called proton-donors.

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