topic 3 - covalent compounds and separation techniques Flashcards
what do covalent bonds form between?
non-metals.
what are covalent bonds?
a shared pair of electrons.
why do atoms share electrons?
to get a full outer shell.
why is there a lot of energy that is needed to break covalent bonds?
because they are strong.
substances with covalent bonds often form what? and give an example?
molecules with low melting and boiling points like hydrogen and water.
why do covalent bonds have low melting and boiling points?
because little energy is needed to break weak intermolecular forces.
why do covalent bonds not conduct electricity?
because they do not have any free electrons or an overall electric charge.
Give the properties of graphite?
it is a form of carbon in which the carbon atoms form layers.
the layers slide over each other, so graphite is much softer than diamond is.
used in pencils and as a lubricant.
each carbon atom in a layer is joined to only 3 other carbon atoms.
it conducts electricity.
Give the properties of diamond?
it is a form of carbon in which each carbon atom is joined to 4 other carbon atoms forming a giant covalent structure.
very hard and has a high melting point.
used in cutting tools.
does not conduct electricity.
what are immiscible liquids?
ones that don’t completely mix together.
what are miscible liquids?
ones that mix together.
what happens when 2 immiscible liquids are shaken together?
they will separate into layers.
give an example of 2 immiscible liquids?
oil and water.
what happens the the denser liquid and the less dense liquid in a separating funnel?
the more dense liquid sinks to the bottom, and the less dense liquid forms a layer on top.
how are layers of immiscible liquids separated?
using a separating funnel and a tap.
what happens when the tap is opened?
it drains off the denser liquid into a beaker.
what does fractional distillation separate?
miscible liquids.
the different liquids in F.D must have what?
different boiling points.
what happens when the mixture of miscible liquids is heated in F.D?
the liquids will condense at different temperatures and can be collected separately.
what is the method for separating out miscible liquids using F.D?
- air is filtered to remove dust.
- it is then cooled to -200 degrees and becomes a miscible mixture of liquids.
- during cooling, water vapour condenses and is removed.
- CO2 freezes and is removed.
- the liquified air then enter F.D column and is heated slowly.
- remaining gases are separated by F.D. Oxygen and argon come out together so another column is used to separate them.
what is the definition of concentration?
measure of how much solute is dissolved in the solvent.
what is the definition of soluble?
a substance which dissolves in a given solvent.
what is the definition of solute?
a solid or a liquid that dissolves in a given solvent from a solution.
what is the definition of solution?
a clear mixture that forms when a solute dissolves in a given solvent.
what is the definition of solvent?
the liquid that dissolves the solute.
what is chromatography used to find out?
which coloured compounds in a mixture contain.
how does chromatography work?
some compounds work better in a solvent than others.
when a solvent moves along a strip of paper, it carries different substances at different speeds so they are separated.
the solvent is called the mobile phase.
the paper contains the stationary phase, through which the solvent and dissolved substances move.
the paper with separated components is called a chromatogram.
how do I complete a chromatography experiment?
- draw a pencil line 1cm from the bottom.
- dot the dye onto the line.
- place into a beaker, with the solvent touching the bottom of the paper, but not the dye.
- cover and leave the solvent to move up the paper.
- when the solvent nears the top, take it out and draw a line to where the solvent reaches.
how can you work out the RF value?
from the value of the spots on a chromatogram.
what is the RF value?
the ratio between the distance traveled by the dissolved substance and the distance travelled by the solvent.
what is the formula for the RF value?
distance traveled by the substance / distance traveled but he solvent.
what are RF values used in?
food industry and forensic science.
scientists use these values and refer to them to identify substances like food additives and drugs.
