Question

Give reason for the following
a) Hydronium ions are always in the form $H_3{O}^{+}$
b) Buttermilk spoils if kept in a copper or brass container

Answer 1

a) Hydrogen atom has one electron and one proton. When this atom loses its electron and is left with only one proton, it forms $H^{+}$ which is hydrogen ion. It is also known as proton as it contains only one proton and nothing else.

Hydronium ion is formed when water is added to $H^{+}$.

$H^{+}+H_{2}O\to H_3{O}^{+}$

b) Copper is less reactive than hydrogen therefore it does not react with acids to liberate hydrogen.

However in the presence of lactic acid in buttermilk the copper does not liberate hydrogen but due to oxidizing property of acid it gets oxidized to $C{u}^2+$ and thus leaches out to buttermilk and gets spoilt.