C2.3 Flashcards
What are covalent bonds
Bonds between two none metals sharing electron/s in their outer shell
What are dog and cross diagrams
A diagram showing the arrangement of electrons in a covalent molecule, using dots to represent electrons from one atom and crosses to represent them from the other
What is a double bond
Two pairs of shared electrons
Properties of simple molecular covalent substances
Strong bonds between atoms but weak forces between molecules.
Low boiling and melting points
Poor electrical conductors as there are no charged particles
Properties of giant molecular covalent substances
Consist of billions of atoms held together by strong covalent bonds so they are very strong
High melting and boiling points as lots of energy needed to break bonds
Apart from graphite, they are poor conductors
Similarities of diamond and graphite
Both carbon molecules
Both have high melting and boiling points as both have many covalent bonds between carbon atoms
Diamond, each carbon is bonded to four others, in graphite they’re only bonded to three
Diamond is much harder as all carbons are joined together by strong covalent bonds
Doesn’t conduct as no free electrons or charged particles
Graphite is soft as strong bonds in layers but weak forces between layers so they easily slide so good for pencils and a lubricant
Good conductor as each carbon atom has a free electron that is free to move, good for electrodes
What are immiscible liquids
Liquids that don’t completely mix and will eventually separate completely after being mixed
How can immiscible liquids be separated
Placing the mixture of the liquids into a separating funnel and allowing them to separate, then drain the Lower layer into a beaker and the other layer into another beaker to separate them
What happens in miscible liquids
When two liquids is, they mix completely and won’t separate
How can miscible liquids be separated
Using a fractional distilation column. Boiling the mixture and condensing the gases, higher boiling point liquids will condense lower in the column and low boiling point liquids will get to the top
How are oxygen and nitrogen separated in the air
Air is first cooled below 0C to freeze any water vapour, this is then removed. The remaining air is then cooled to -200C to liquids it. This mixture is then pumped into the fractional distillation column and warmed to -185C. This causes the nitrogen to evaporate as it boils so it can be collected at the top of the column and most of the oxygen will stay at the bottom so can be pumped out. Some of the oxygen will evaporate but it will condense again nearer the top offt he column and run back down to the bottom
What is chromatography used for
To identify different colourings in substances.
How does chromotography work
Samples are applied to the bottom of a special paper. The bottom of the paper is then suspended into a solvent. The solvent will be soaked up into the paper, and move up it. As it passes the samples, the different compounds in the samples will move with the solvent as they dissolve into it. Some compounds will be more soluble in that solvent than others so will travel further up the paper. This separates the different substances
What is the rf value for and how is it worked out
It is a value for a substance that doesn’t change aslong ad the conditions of a chromatography are the same so it can be used to identify substances. It’s worked out by
Rf = distance compound moved / distance solvent moved
Uses of chromatography
Used by food standard agencies to see what colourings in foods are being used to make sure they’re safe
Used by the police so see if a suspect was at s crime scene
Used by museum staff when restoring paintings to see which dyes have been used to make it more accurate and to identify forgeries by seeing if that paint existed at the time it was supposibly painted
