C2 Topic 3 - Covalent Compounds And Separation Techniques Flashcards
What is an intermolecular bond?
Intermolecular bonds are very weak bonds of attraction between different molecules. This allows covalent compounds to melt and boil without the atoms becoming separate. When heated, the intermolecular bonds break and the chemical changes state.
Describe the properties of a giant molecular covalent substance.
Similar to ionic lattices except no charged ions
All atoms are bonded to each other with strong covalent bonds
High melting and boiling points
Don’t conduct electricity
Normally insoluble
State some properties of diamond.
Each carbon has four covalent bonds
Very rigid and hard
Doesn’t conduct electricity as there are no free electrons
State some properties of graphite.
Each carbon has three covalent bonds, the fourth electron is delocalised
Can conduct electricity
Made up of layers which slide over each other easily
Explain the difference between a miscible and immiscible liquid mixture.
Miscible liquids mix together because they have similar densities. Immiscible liquids, such as oil and water, will never mix properly as they have different densities, so oil always floats above water.
How do you separate two immiscible liquids?
Pour the mix into a separating funnel and wait a few minutes. The denser liquid will fall to the bottom while the less dense one will float to the top. Open the tap to drain out the bottom liquid into a beaker.
How do you separate two miscible liquids?
Fractional distillation - so long as the liquids have different boiling points, they can be separated with this method. The mixture is heated up to the lower boiling point of the two liquids. The evaporated gas is collected leaving the other one in the distillation column.
How is chromatography used to identify substances?
Chromatography works on the principle that different substances wash through wet filter paper at different rates.
How do you calculate the Rf value of a chemical?
Rf = distance travelled by substance / distance travelled by solvent
What is covalent bonding?
When two or more non-metals bond, they share electrons rather than give/take them away. This makes them weaker than ionic bonds, but all the atoms have full shells anyway.
