easy ion problems

1.
A compound is a substance which can exist. Compounds can be divided into two classes : ionic compounds and covalentcompounds.

Ionic compounds are composed of cations (positive ions) and anions (negativeions). If a cation or anion is made oftwo or more atoms, it is called a polyatomic ion.
e.g.1 In ammonium chloride, the cation (ammonium ion) is a polyatomic ion.
e.g.2 In sodium sulphate, the anion (sulphate ion) is a polyatomic ion.
e.g.3 In ammonium chloride, the cation and the anion are polyatomic ions.

No matter whether the ions are polyatomic ions or not, the bonding betweencations and anions are ionic bonds, and thus the compound is an ionic compound. Atoms are held togetherto make a polyatomic ion. However, polyatomic ion is just a kind of ion, andions make ionic compounds.

Polyatomic ions are just a part of ionic compounds. An ionic compound can exist, but only a kindof polyatomic ions (e.g. only ammonium ions without any anion) cannot existalone.


2.
In laboratory :

Silver ions are formed by the reaction between silver and concentrated nitricacid. Silver reacts with concentratednitric acid to give silver nitrate solution (containing silver ions), water andnitrogen dioxide gas.

Ammonium ions are formed by the neutralization between ammonia solution and anacid. For example, ammonia solution isneutralized by dilute hydrochloric acid to give ammonium chloride (containingammonium ions) and water.

lead(II) ion are formed by the reaction between between lead and concentratednitric acid. Lead reacts withconcentrated nitric acid to give lead(II) nitrate solution (containing lead(II)ions), water and nitrogen dioxide gas.