Question

Which formula represents copper(I) oxide? (1) CuO (3) Cu2O (2) CuO2 (4) Cu2O2

Answer 1

Answer : The correct formula of copper(I) oxide is, (3) $Cu_2O$

Explanation :

Copper(I) oxide is an ionic compound because copper element is a metal and oxide element is a non-metal. The bond formed between a metal and a non-metal is always ionic in nature.

The nomenclature of ionic compounds is given by:

• Positive ion is written first.
• The negative ion is written next and a suffix is added at the end of the negative ion. The suffix written is '-ide'.
• In case of transition metals, the oxidation state are written in roman numerals in bracket in-front of positive ions.

The charge on copper is (+1) and the the charge on oxide is (-2). The charges are not balanced.  The charges are balanced by the criss-cross method.

Hence, the formula of copper(I) oxide is, $Cu_2O$

Answer 2

The answer is (3) Cu2O. Copper (I) has an oxidation state of +1 (that's what the "I" indicates). You can also think of this as copper (I) having a charge of +1. Oxygen has an oxidation state of -2 (that's just a rule you have to know), and you can think of it as oxygen having a charge of -2. You need oxidation numbers in a neutral compound to add up to 0 (or charges in a neutral compond to add up to 0), so you need two Cu to balance the O, which is Cu2O.