Using Stock notation, represent the following compounds :HAuCl4, Tl2O, FeO, Fe2O3, CuI, CuO, MnO and MnO2.

Question

Accepted Answer

> [!TLDR]
> Stock notation writes the oxidation state of the metal as a Roman numeral in
> parentheses directly after the metal's symbol in the formula. Working out each metal's
> oxidation number and inserting it gives: **HAu(III)Cl₄, Tl₂(I)O, Fe(II)O, Fe₂(III)O₃,
> Cu(I)I, Cu(II)O, Mn(II)O and Mn(IV)O₂.**

## The Concept: What Stock Notation Is

Many metals show **variable oxidation states** — iron can be +2 or +3, copper +1 or +2,
manganese anything from +2 to +7. A bare formula like FeO vs Fe₂O₃ forces you to work the
state out each time. The German chemist Alfred Stock's solution: write the oxidation
number as a **Roman numeral in parentheses immediately after the metal's symbol in the
molecular formula** — Fe(II)O, Fe₂(III)O₃. That is Stock notation: the representation is
the *formula with the Roman numeral inserted*, not an English name.

The procedure is always the same: assign the known oxidation numbers (O = $-2$, halogens
= $-1$ here, H = $+1$), let the metal be $x$, and use the rule that the oxidation numbers
of a neutral compound sum to zero.

## Working Out Each Metal

**1. HAuCl₄** — H is $+1$, each Cl is $-1$:
$(+1) + x + 4(-1) = 0 \Rightarrow x = +3$. Gold is in the **+3** state.

**2. Tl₂O** — O is $-2$: $2x + (-2) = 0 \Rightarrow x = +1$. Thallium is **+1**.

**3. FeO** — $x + (-2) = 0 \Rightarrow x = +2$. Iron is **+2**.

**4. Fe₂O₃** — $2x + 3(-2) = 0 \Rightarrow x = +3$. Iron is **+3**.

> [!WARNING]
> A common mistake is to confuse FeO and Fe₂O₃. FeO has Fe in the +2 state, Fe₂O₃ has Fe
> in the +3 state — exactly the ambiguity Stock notation exists to remove.

**5. CuI** — I is $-1$: $x + (-1) = 0 \Rightarrow x = +1$. Copper is **+1**.

**6. CuO** — $x + (-2) = 0 \Rightarrow x = +2$. Copper is **+2**.

**7. MnO** — $x + (-2) = 0 \Rightarrow x = +2$. Manganese is **+2**.

**8. MnO₂** — $x + 2(-2) = 0 \Rightarrow x = +4$. Manganese is **+4**.

## Writing the Stock Representations

Insert each Roman numeral after the metal's symbol:

| Compound

Compound	Calculation	Stock notation
$\ce{HAuCl4}$	$+1 + x + 4(-1) = 0 \Rightarrow x = +3$	$\ce{HAu(III)Cl4}$
$\ce{Tl2O}$	$2x + (-2) = 0 \Rightarrow x = +1$	$\ce{Tl2(I)O}$
$\ce{FeO}$	$x + (-2) = 0 \Rightarrow x = +2$	$\ce{Fe(II)O}$
$\ce{Fe2O3}$	$2x + 3(-2) = 0 \Rightarrow x = +3$	$\ce{Fe2(III)O3}$
$\ce{CuI}$	$x + (-1) = 0 \Rightarrow x = +1$	$\ce{Cu(I)I}$
$\ce{CuO}$	$x + (-2) = 0 \Rightarrow x = +2$	$\ce{Cu(II)O}$
$\ce{MnO}$	$x + (-2) = 0 \Rightarrow x = +2$	$\ce{Mn(II)O}$
$\ce{MnO2}$	$x + 2(-2) = 0 \Rightarrow x = +4$	$\ce{Mn(IV)O2}$

Compound	Oxidation state of metal	Stock notation
HAuCl₄	Au = +3	HAu(III)Cl₄
Tl₂O	Tl = +1	Tl₂(I)O
FeO	Fe = +2	Fe(II)O
Fe₂O₃	Fe = +3	Fe₂(III)O₃
CuI	Cu = +1	Cu(I)I
CuO	Cu = +2	Cu(II)O
MnO	Mn = +2	Mn(II)O
MnO₂	Mn = +4	Mn(IV)O₂

Q.Using Stock notation, represent the following compounds :HAuCl4, Tl2O, FeO, Fe2O3, CuI, CuO, MnO and MnO2.

Concept understanding — Stock Notation

Stock Notation — Naming the Oxidation State

The Core Idea

How to Write It

Why It Matters

Common Mistakes

Exam Relevance

The Concept: What Stock Notation Is

Working Out Each Metal

Writing the Stock Representations

Q.Using Stock notation, represent the following compounds :HAuCl4, Tl2O, FeO, Fe2O3, CuI, CuO, MnO and MnO2.

The Concept: What Stock Notation Is

Working Out Each Metal

Writing the Stock Representations

🎓Unlock everything free for 14 days

Unlock everything free for 14 days