1elements, compounds and mixtures Flashcards
element
a substance made up of atoms that all contain the same number of protons and cannot be split into anything simpler
compound
a pure substance made up two or more elements chemically combined together. there are unlimited types of compounds. cannot be separated by physical methods of separation
mixture
a combination of two or more substances that are not chemically joined together. can be separated by physical methods of separation
pure substances
melt and boil and specific and sharp temperatures
mixtures have
a range of melting and boiling points as they consist of different substances that tend to lower the melting point and broaden the melting point range
melting and boiling points data can be used to
distinguish pure substances from mixtures
melting point analysis is routinely used to accesss the
purity of drugs
the influence of impurities can be seen more clearly on
heating / cooling curves
simple distillation is used to
separate a liquid and soluble solid from a solution or a pure liquid from a mixture of liquids
how does simple distillation work
the solution is heated and pure water evaporates producing a vapour which rises through the neck of the round bottomed flask. the vapour passes through the condenser where it cools and condenses, turning into the pure liquid that is collected in a beaker. after all the water is evaporated from the solution, only the solid solute will be left behind
fractional distillation is used to
separate two or more liquids that are miscible with one another
how does fractional distillation work
the solution is heated to the temperature of the substance with the lowest boiling point. this substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid the will be collected in a beaker. all of the substance is evaporated and collected, leaving behind the other components of the mixture.
filtration is used to
separate an undissolved solid from a mixture of the solid and a liquid/ solution
how does filtration work
a piece of filter paper is placed in a filter funnel above a beaker. a mixture of insoluble solid and liquid is poured into the filter funnel. the filter paper will only allow small liquid particles to pass through as filtrate. solid particles are too large to pas through the filter paper so will stay behind as a residue
crystallisation is used to
separate a dissolved solid from a solution when the solid is much more soluble in hot solvent than in cold
how does crystallisation work
the solution is heated, allowing the solvent to evaporate, leaving a saturated solution behind. test if the solution is saturated by dipping a clean, dry, cold glass rod into the solution- if solution is saturated crystals will form on the rod. the saturated solution is allowed to cool slowly, crystals begin to grow as solids will come out of solution due to decreasing solubility. the crystals are collected by filtering the solution, they are washed with cold distilled water to remove impurities and are allowed to dry.
paper chromatography is used to
separate substances that have different solubilities in a given solvent
how does paper chromatography done
a pencil line is drawn on chromatography paper and spots of the sample are placed on it. pencil is used for this as ink would run into the chromatogram along with the samples. the paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent so the samples don’t wash into the solvent container. the paper is called the stationary phase. the solvent travels up the paper by capillary action, taking some of the coloured substances with it; it is called the mobile phase. different substances have different solubilities so will travel at different rates causing the substances to spread apart. this will show the different components of the ink/dye. if two or more substances are the same they will produce identical chromatograms. if the substance is a mixture it will separate on the paper to show all the different components as separate spots. an impure substance will show up with more than one spot, a pure substance should only show up with one spot
pure substances will produce
only one spot on the chromatogram
if two or more substances are the same
they will produce identical chromatograms
if the substance is a mixture it will
separate on the paper to show all the different components as separate spots.
an impure substance will produce
a chromatogram with more than one spot
Rf values are used to
identify the components of mixtures
the Rf value of a particular compound is always
the same but it is dependant on the solvent used- if the solvent changes then the value changes
