Covelent Compunds And Separation Techniques Flashcards
What is a covalent bond.
A bond between a pair of electrons in the outer shell of two atoms.the electrons are shared between the atoms so they both have full outer shells
What is a double bond
A bond where atoms share two pair of electrons such as in O2
What are simple covalent molecular substances and properties
Substances with weak forces between neighbouring molecules so they are usually gas with low melting and boiling points. They are poor conducteurs as they have not lost or gained any particles so they are poor conductors
What are giant molecular covalent substances and properties
They are substances that can consist of billions of atoms joined together by covalent bonds. Covalent bonds are very strong so these substances have high melting and boiling points.
What are similarités and differences between graphite and diamond
Similarities
Both made of carbon atoms
Both have high melting and boiling points because of the covalent bonds between the carbon atoms.
Differences
Diamond is very hard because all atoms are joined by covalent bonds whereas graphite is very soft as although there are strong bonds between carbon atoms, there are weak forces between layers.
Diamond is good for cutting and graphite can be used as a lubricant and in pencils
Diamond doesn’t conduct as there are no free electrons or charged particles to move around
Graphite is a good conductor as there is one free electron in every carbon atom that can move freely
What are immiscible liquids
Liquids that don’t mix even when shaken, they still separate
How can you separate imiscible liquids
Putting them in to a separating funnel and letting them separate, then drain the lower liquid to separate them
What are miscible liquids
Liquids that can be mixed into a solution that won’t separate
How can you separate miscible liquids
By using a fractional disriallation column. Separating the liquids by boiling one of them away.
How can air be separated
By cooling the air to -200 which is less than the boiling points of all the gases so they are all liquid. This solution is then put into the warmer fractional distillation column which is around -185 Celsius. This is below oxygens boiling point so it’s a liquid that can be piped out but nitrogen is still a gas so can be collected at the top of the column
What is chromatography used for
To separate colourings in substances
How does chromatography work
Samples are applied to the bottom of a special paper. The paper is then held suspended with the bottom in the solvent. Different compounds are more soluble than others so are carried by the solvent up the paper at different speeds. After a while, the solvent will have separated the compounds in the sample to make a chromatogram
What is an Rf value and what is its formula
This is the value used to identify a compound as it doesn’t change for a compound as long as the chromatography conditions are same. It is worked out by dividing the distance the compound has risen by the distance the solvent has risen.
What is chromatography used for
To separate food colourings to make sure only safe food colourings are used
By museums to work out the mixture used in a paint so restorations use the exact same colour
Used but eh police on DNA samples to see if a suspect was present at a crime scene
