Question

Write down formulae for the following ions: (a) manganate(VII); (b) manganate(VI); (c) dichromate(VI); (d) vanadyl; (e) vanadate (ortho and meta); (f) hexacyanoferrate(III). Give an alternative name for manganate(VII).

Short answer

(a) \( \text{MnO}_4^- \) (permanganate); (b) \( \text{MnO}_4^{2-} \); (c) \( \text{Cr}_2\text{O}_7^{2-} \); (d) \( \text{VO}^{2+} \); (e) ortho \( \text{VO}_4^{3-} \), meta \( \text{VO}_3^- \); (f) \( \text{Fe(CN)}_6^{3-} \).

Step-by-step solution

Understanding Manganate(VII)

Manganate(VII) ions are represented by the chemical formula \( \text{MnO}_4^- \). These ions have a -1 charge and are often referred to by their alternative name, permanganate ions.

Identifying Manganate(VI)

Manganate(VI) ions are represented by the chemical formula \( \text{MnO}_4^{2-} \), where the ion has a -2 charge. It's different from manganate(VII) as it has a different oxidation state of manganese.

Expressing Dichromate(VI)

The dichromate(VI) ion is given by the formula \( \text{Cr}_2\text{O}_7^{2-} \). The 'VI' indicates the oxidation state +6 of chromium in the ion.

Defining Vanadyl Ion

The vanadyl ion is represented by the formula \( \text{VO}^{2+} \). The formula shows that this ion has a +2 charge and involves vanadium in the +4 oxidation state.

Describing Vanadate Ions

Ortho-vanadate is represented by \( \text{VO}_4^{3-} \), which indicates a tetrahedral anion with a -3 charge. Meta-vanadate is given by \( \text{VO}_3^- \), which is a different isomeric form of vanadate.

Determining Hexacyanoferrate(III)

Hexacyanoferrate(III) is denoted by the symbol \( \text{Fe(CN)}_6^{3-} \). This formula shows iron coordinated with six cyanide ions and the entire complex carrying a -3 charge.

Key concepts

Manganate Ions

Manganate ions come in two main forms, manganate(VII) and manganate(VI). These are important in various chemical reactions and are often examined in their distinct differences.
- **Manganate(VII):** This ion is chemically represented as \( \text{MnO}_4^- \). The 'VII' signifies that the manganese atom is in a +7 oxidation state. It carries a -1 charge. Manganate(VII) is also known by another name: **permanganate**. This name is commonly used, especially in laboratory and industrial settings, due to its wide range of applications in oxidation reactions.
- **Manganate(VI):** Unlike its counterpart, manganate(VI) has the formula \( \text{MnO}_4^{2-} \), with manganese in a +6 oxidation state. It carries a -2 charge. The change in oxidation state significantly alters the ion's properties, making it less oxidizing compared to manganate(VII).
Both manganese ions are key in redox reactions where they are reduced to lower oxidation states, participating actively in the process.

Dichromate Ion

The dichromate ion is an essential inorganic ion with the formula \( \text{Cr}_2\text{O}_7^{2-} \). In this ion, chromium is in a +6 oxidation state.
- The dichromate ion functions primarily as an oxidizing agent in various chemical processes. It is particularly useful in qualitative analysis and in laboratory oxidation reactions.
- **Color and Usage:** Dichromate solutions are characteristically orange, a trait that lends itself well to visual identification in reactions. Due to its oxidizing ability, it is often used in processes like chromate conversion coating and as a cleaning agent for laboratory glassware.
- Included in the ion is a robust chromium-oxygen framework that contributes to its stability, which is why it can exist freely in solution without rapid decomposition.

Vanadyl Ion

Vanadyl ions are another interesting facet of inorganic chemistry, particularly due to vanadium's variable oxidation states.
- **Chemical Formula:** \( \text{VO}^{2+} \). Here, vanadium exists in a +4 oxidation state, and the ion carries a +2 charge.
- **Structure and Characteristics:** Vanadyl ions are often characterized by their sky-blue color when in solution, which can be informative when analyzing substances with unknown compositions. The ion's geometry typically assumes a square pyramidal shape, contributing to its unique chemical properties.
- **Applications:** Vanadyl ions have a role in various biological systems and are also studied for their significance in redox reactions. They are often involved in catalytic cycles and materials containing vanadyl groups are studied for applications in battery technology.

Vanadate Ion

Vanadate ions occur in a few distinct forms, chiefly ortho-vanadate and meta-vanadate, each differing in their structure and charge.
- **Ortho-vanadate Ion:** This ion is expressed as \( \text{VO}_4^{3-} \). It holds a tetrahedral shape with a -3 charge. The ortho-form is typically encountered in various mineral and biological contexts, providing a staple for phosphate substitutions in biochemistry.- **Meta-vanadate Ion:** With the formula \( \text{VO}_3^- \), this isomer of vanadate is different mainly in geometry and charge, possessing a -1 charge. It is less commonly found than ortho-vanadate but still important in certain chemical contexts.
Vanadate ions are involved in biological systems as phosphate analogues and are studied for their enzyme inhibition capabilities in metabolic pathways.

Hexacyanoferrate

Hexacyanoferrate ions come in several forms but are distinguished by their association with iron, showcasing complex ion chemistry.
- **Hexacyanoferrate(III):** With the chemical representation \( \text{Fe(CN)}_6^{3-} \), this ion consists of iron in a +3 oxidation state, coordinated with six cyanide ions. The entire complex exhibits a -3 charge.
- **Properties:** This complex exhibits significant stability which is utilized in various chemical applications such as electroplating and as anti-caking agents in salt. Its deep coloration also makes it useful as a pigment.
- **Safety and Usage:** While cyanide ions are usually toxic, the hexacyanoferrate complex is quite stable, making it surprisingly safe to handle within typical use cases, though care must always be taken when working with cyanide compounds. Hexacyanoferrates are integral to many chemical processes, including the formation of Prussian blue, a noted pigment.