LEARNATHON
III

Competition for grade 6 to 10 students! Learn, solve tests and earn prizes!

### Theory:

Metals such as gold and silver are known to be unreactive to both $$HCl$$ and $$HNO_3$$. On the other hand, the combination of these two acids will dissolve gold. This mixture is called aquaregia.
It is a $$3:1$$ combination of hydrochloric acid and nitric acid that has been properly prepared. It's a fuming yellow-orange liquid, It is a highly corrosive liquid that can attack gold and other resistant substances. The chemical formula of aquaregia is $$3$$$$HCl+HNO_3$$. It is miscible in water.

Aquaregia is a Latin word that means "King's Water". The name reflects the ability of aquaregia to dissolve noble metals such as gold, platinum and palladium.

Uses of aquaregia:
• The most common application of aquaregia is in the Wohlwil process, which is used to refine gold. During this process, we obtain high purity gold ($$99.999%$$).
• It is used in the itching of various metals.
• It is also used to remove metals like gold and platinum.
Base
Already we have studied that in an aqueous solution, an acid can produce hydrogen ions ($$H^+$$), while a base can produce hydroxyl ions ($$OH^-$$). When an acid and a base react, a neutral product is formed, which is called salt.
According to Arrhenius theory, bases are substances that ionise in water to form hydroxyl ions ($$OH^-$$).
$\begin{array}{l}\mathit{NaOH}\phantom{\rule{0.147em}{0ex}}\stackrel{}{⟶}\phantom{\rule{0.147em}{0ex}}{\mathit{Na}}^{+}+{\mathit{OH}}^{-}\\ \mathit{Base}\phantom{\rule{3.381em}{0ex}}\mathit{Hydroxyl}\phantom{\rule{0.147em}{0ex}}\mathit{ion}\end{array}$

Some metal oxides give salt and water on reaction with acids. These are also called bases. Bases that are soluble in water are called alkalis.

$\begin{array}{l}{\mathit{ZnO}}_{\left(s\right)}+{2\mathit{HCl}}_{\left(l\right)}\phantom{\rule{0.147em}{0ex}}\stackrel{}{⟶}\phantom{\rule{0.147em}{0ex}}{\mathit{ZnCl}}_{2\left(\mathit{aq}\right)}+{{H}_{2}O}_{\left(l\right)}\\ \mathit{Zinc}\phantom{\rule{0.147em}{0ex}}\mathit{oxide}\end{array}$

When a base reacts with water, salt and water are produced.

$\mathit{Base}\phantom{\rule{0.147em}{0ex}}+\phantom{\rule{0.147em}{0ex}}\mathit{Acid}\phantom{\rule{0.147em}{0ex}}\stackrel{}{⟶}\phantom{\rule{0.147em}{0ex}}\mathit{Salt}\phantom{\rule{0.147em}{0ex}}+\phantom{\rule{0.147em}{0ex}}\mathit{Water}$

Bases contain one or more replaceable oxide or hydroxyl ions in solution.
Important!
All alkalis are bases, but not all bases are alkalis. For example $$NaOH$$ and $$KOH$$ are alkalis, whereas $$Al(OH)_3$$ and $$Zn(OH)_2$$ are bases.