Covalent compounds and separation techniques Flashcards
what is a covalent bond
a covalent bond is a pair of electrons that is shared between two atoms.
what does covalent bonding result in
the formation of molecules
Explain the formation of simple molecular, covalent substances using dot and cross diagrams, including: a hydrogen b hydrogen chloride c water d methane e oxygen f carbon dioxide
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Classify different types of elements and compounds by
investigating their melting points and boiling points, solubility in water and electrical conductivity (as solids and in solution) including sodium chloride, magnesium sulphate, hexane, liquid
paraffin, silicon(IV) oxide, copper sulfate, and sucrose (sugar)
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what can substances with covalent bonds form
small molecules or giant structures
give features of simple molecular covalent structures
> strong covalent bonds between the atoms > weak forces between the molecules. > low melting and boiling points > liquids or gases at room temperature > solids with low melting points > no charged particles > do not conduct electricity
give features of giant molecular covalent substances
> covalent bonds are strong
takes a lot of energy to break these bonds so melting points and boiling points are very high
very hard and don not conduct electricity
give two examples of giant covalent substances
diamond and graphite
describe the uses and features of diamond and graphite
diamond is used for cutting tools as it is very hard. graphite is used as a lubricant because the forces between the layers are weak and the layers can slide over each other easily. in graphite, there is one electron from each carbon atom that can move along the layers, so graphite conducts electricity an can be used to make electrodes
what are miscible and immiscible liquids
miscible liquids mix completely with each other. immiscible liquids do not mix completely.
Describe the separation of two immiscible liquids using a
separating funnel
> place mixture in funnel and put a beaker underneath
open the tap until most of the lower liquid has run into the beaker
put a clean beaker under the funnel and run the last bit of the lower liquid and a little bit from the top liquid into the beaker. place a final clean beaker under the tap and run off all of the second liquid
how can miscible liquids be separated
using fractional distillation
describe the process of using fractional distillation to separate miscible liquids
> mixture is heated, and vapours pass into a fractionating column
as the gases cool down, the ones with the highest boiling points condense first.
different liquids are collected at different places in the column
what is chromatography
can be used to separate and identify components of mixtures, including colouring agents in foodstuffs
what is the Rf value of a compound
one distance divide by another, so it has no units, it is always the same as long as the chromatography is carried out in the same way, under the same conditions.
