Edexcel IAL Chemistry 8.3 Roman numerals in chemical names

Calculate the central element's oxidation state from the formula and charge, then write that value as a Roman numeral rather than an ionic charge.

Exam points

Interpret a Roman numeral as the named element's oxidation number, not an ion charge.
Name chlorate or sulfate species by calculating and writing the correct Roman numeral.

[Maximum number: 1]

Chlorine dioxide, $\mathrm{ClO}_{2}$ , can be used to treat water to make it safe for drinking. The molecule is a free radical. One suggested structure is shown.

Figure for Question 8.3—Indicate the oxidation number of an element in a compound or an ion question 1 — Edexcel A-Level Chemistry AS

Chlorine dioxide can be made from potassium chlorate(V), $\mathrm{KClO}_{3}$ , in a two-step process.

Step 1 Potassium chlorate(V) reacts with concentrated sulfuric acid to form compound A.

Step 2 Compound A then undergoes a disproportionation reaction to form chlorine dioxide and hydrogen chlorate(VII), $\mathrm{HClO}_{4}$ .

State the meaning of the Roman numerals in chlorate(V) and chlorate(VII).

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8.3—Indicate the oxidation number of an element in a compound or an ion question 1