Question

(a) Describe the structural features of graphite which make it suitable for intercalation reactions. (b) How does the structure of the first stage intercalate of graphite differ from that of the parent material? (c) Reaction of excess potassium with graphite produced the goldcoloured compound A which contained \(28.9 \%\) potassium. Describe the type of reaction occurring, and explain the differences in appearance and conductivity of the new material compared with graphite.

Short answer

(a) Graphite is composed of carbon atoms arranged in layers in a hexagonal pattern. These layers are held together by weak van der Waals forces, allowing them to slide over each other. This structure makes graphite suitable for intercalation reactions as other atoms or molecules can be inserted between the layers without significantly disrupting the graphite structure. (b) The first stage intercalate of graphite has intercalating species, such as alkali metals, inserted between every alternate graphite layer. This increases the distance between adjacent carbon layers but preserves the overall structure. (c) The reaction of excess potassium with graphite is an intercalation redox reaction, forming a compound containing 28.9% potassium. This new gold-coloured material, compound A, differs from graphite in appearance and conductivity. The presence of potassium ions modifies the electronic structure of the graphite layers, altering their color. Due to the donated electrons from potassium, compound A exhibits higher electrical conductivity than graphite, as the potassium ions delocalize extra electrons within the carbon layers, leading to a more effective charge transfer.

Step-by-step solution

1. Structural features of graphite

Graphite is composed of layers of carbon atoms arranged in hexagonal rings. These layers are held together by weak van der Waals forces, allowing for the layers to slide over each other easily. This characteristic makes it suitable for intercalation reactions because intercalating atoms or molecules can insert themselves between these layers without significantly disrupting the overall structure of graphite.

2. Structure of the first stage intercalate of graphite

In the first stage intercalate of graphite, intercalating species such as alkali metals are inserted between every alternate layer of graphite. This results in a structure where the intercalating species are evenly distributed between the carbon layers, increasing the distance between adjacent carbon layers but maintaining the overall structure of graphite.

3. Reaction of excess potassium with graphite

When excess potassium reacts with graphite, intercalation occurs, forming a new intercalation compound, A, which contains 28.9% potassium. This can be considered a redox reaction as the potassium donates electrons to the graphite layers, generating K+ cations and increasing the separation between the carbon layers.

4. Differences in appearance and conductivity between compound A and graphite

The new material, compound A, has a gold-coloured appearance, as opposed to the black or gray color of graphite. This is due to the presence of potassium ions that modify the electronic structure of the graphite layers, altering their optical properties. The conductivity of compound A is different from that of graphite as well. Due to the donated electrons from potassium to the graphite layers, compound A exhibits higher electrical conductivity compared to graphite. The inserted potassium ions serve to delocalize extra electrons within the carbon layers, leading to a more effective charge transfer between layers, thus increasing the compound's overall electrical conductivity.