C2 Flashcards
What are the two phases in chromatography?
`A stationary phase that does not move. A mobile phase that does move
What is the stationary phase in paper chromatography?
The absorbent paper
What is the stationary phase of gas chromatography?
Silica or alumina powder packed into a metal column
Why can carbon form many different compounds?
It has 4 valence electrons and can form 4 covalent bonds. It can join with other carbon atoms to form chains and rings or form covalent bonds with other elements
Why are diamond and graphite different?
Because they have different structure and bonding
What is a nanotube?
A sheet of graphene rolled into a tube. Strong. Used to reinforce some sports equipment.
Why are metals malleable?
Metal ions are held in a lattice by forces that attract them to a sea of delocalised electrons. When a large enough force is applied layers of metal ions slide over one another but delocalised electrons are free to move so overall no bonds are broken.
What is a material made from nanoparticles called?
Nanoparticulate
Risks of nanoparticles
- May be breathed in, absorbed by skin or pass into cells
- May take a long time to break down once released into environment and toxic substances may stick to their surfaces
- Harmful to health and environment in ways difficult to predict, with risks difficult to determine
What is bonding in a simple molecule like?
- Covalent bonds involve electrostatic forces of attraction but the forces are between the nucleus of each bonded atom and the shared electrons
- Covalent bonds are strong. Intermolecular forces are weak.
What is a phase?
A substance in the solid, liquid or gas state.
What is the mobile phase in paper chromatography?
A solvent in the liquid state
What is thin layer chromatography?
Same way as paper chromatography, but stationary phase is a thin layer of silica or alumina powder spread over a plate of glass or plastic
What are Rf values?
Compare the different spots on a chromatogram
What is the mobile phase in gas chromatography?
Inert carrier gas such as nitrogen
What does gas chromatography do?
Separates components and measures their amounts
What happens in gas chromatography?
- Sample is turned into gas state and injected into column
- Different components take different times to travel through the column, depending on how strongly they bind to the stationary phase
- A detector sends a signal to a computer as each component leaves the column
- The computer produces a chromatogram in which each component is a peak plotted against the travel time
How to calculate Rf values?
Distance travelled by substance/distance travelled by solvent
What are the advantages of thin-layer chromatography?
Quicker, more sensitive, there are more choices of stationary phases and solvents to use
How to choose separation method?
- Insoluble and soluble substance -filtration
- A solute dissolves in solvent - crystallisation or simple distillation
- Two or more liquids-fractional distillation
- Coloured soluble substances- paper or thin-layer chromatography
What is a diamond like?
- Transparent and very hard
- Exists as a giant covalent structure where each carbon atom is covalently bonded to 4 other carbon atoms
- Has very high melting point
- No delocalised electrons as all valence electrons are shared so it doesn’t conduct electricity.
What is an allotrope?
Different forms of an element in the same state but with different atomic arrangements
What is graphite like?
- Grey-black and soft
- Giant covalent structure where each carbon atom is covalently bonded to three other, so one electron is not shared so it becomes delocalised and is free to move through the structure.
- It conducts electricity even though it is a non-metal. Has a layered structure
- Atoms in each layer form interlocking hexagons
- Very high melting point
- Forces between layers are weak so layers can slide over easily
- Graphite is hence slippery, used in pencil.