Understanding Mixtures and Separation Techniques

Mixtures and Separation
L/O – explain how to separate different mixtures
Last week:
 
Define
 the terms:
Dominant allele
Recessive allele
Last term: 
Describe
 the advantages of an electron microscope
Last Year: 
An object was magnified 250
times to produce an image that was
40mm across. 
Calculate
 the actual size of
the object.
Key Words
Mixtures
Chromatography
Crystallisation
Filtration
Distillation
A pure substance has only one type of molecule in it.
Identify which of these diagrams show a 
pure substance
A pure substance has only one type of molecule in it.
The circled diagrams
all show a 
pure
substance
 because
they only have one
type of molecule.
 
 
pure
 substance consists only of one 
element
 or
one 
compound
mixture
 consists of two or more different substances, not
chemically joined together
 
 
A pure substance has a fixed melting and boiling point.
 
An impure substance melts and boils at a range of different
temperatures
Bronze
: 
Describe
 the difference between a 
pure substance 
 and an
impure substance
.
Silver: 
Justify
 why 
G
 is a mixture (impure substance) but 
I
 is a pure
suibstance
Gold: 
Explain why a 
mixture
 of different substances might not have
a 
single melting temperature
.
 
 
Filtration
Filtration allows you to separate an 
insoluble solid
 from a 
liquid
The liquid is able to pass through the 
filter paper
 but the solid
cannot.
 
 
Crystallisation
If you have a 
soluble solid
 dissolved in a liquid, you cannot
separate them by filtration.
You can 
evaporate
 the liquid, leaving behind the solid. This works
because the solid has a much higher 
boiling point
 than the liquid
 
 
Filtration and crystallisation can be used together if you have both
a soluble solid and insoluble solid.
 
For example a mixture of sand, salt and water.
 
https://www.youtube.com/watch?v=vi_SJBnxmHo
 
 
Bronze
: 
Produce
 a clear, labelled diagram showing how filtration
and crystallisation can be carried out.
Silver: 
Justify
 why filtration and separation can’t always be used for
the same mixtures.
Gold: 
Evaluate
 the methods for both filtration and crystallisation.
Identify any possible mistakes that could be made and hazards
when carrying them out.
 
 
Chromatography
Paper chromatography is used to separate mixtures of soluble
substances. These are often coloured substances such as food
colourings, inks, dyes or plant pigments.
 
 
Chromatography
Some inks dissolve more easily than others. This means they will
move up the paper faster.
 
 
Chromatography
In chromatography there are 2 phases:
 
Stationary phase – the paper (it doesn’t move)
Mobile phase – the solvent / liquid (it does move)
 
 
Chromatography
Separation by chromatography produces a chromatogram. A
paper chromatogram can be used to distinguish between pure
and impure substances:
 
a pure substance produces one spot on the chromatogram
an impure substance, or mixture, produces two or more spots
 
 
Chromatography
For each spot you can calculate the Rf value.
The Rf value tells you how easy it was for that substance to
dissolve and move up the paper.
 
Exam Practice
. Attempt each of the following exam questions
 
 
 
 
 
 
Self Assess your answers
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Explore the concepts of mixtures and separation, from the definition of dominant and recessive alleles to the advantages of electron microscopes. Learn about identifying pure substances, differences between pure and impure substances, and techniques like filtration and crystallization for separation. Discover why mixtures may not have a single melting temperature and the distinctions between pure substances like bronze and impure substances like G and I.


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  1. Mixtures and Separation L/O explain how to separate different mixtures Last week:Define the terms: Dominant allele Recessive allele Last term: Describe the advantages of an electron microscope Last Year: An object was magnified 250 times to produce an image that was 40mm across. Calculate the actual size of the object. Actual size = Key Words Mixtures Chromatography Crystallisation Filtration Distillation Image size magnification

  2. A pure substance has only one type of molecule in it. Identify which of these diagrams show a pure substance

  3. A pure substance has only one type of molecule in it. The circled diagrams all show a pure substance because they only have one type of molecule.

  4. A pure substance consists only of one element or one compound A mixture consists of two or more different substances, not chemically joined together

  5. A pure substance has a fixed melting and boiling point. An impure substance melts and boils at a range of different temperatures

  6. Bronze: Describe the difference between a pure substance and an impure substance. Silver: Justify why G is a mixture (impure substance) but I is a pure suibstance Gold: Explain why a mixture of different substances might not have a single melting temperature.

  7. Filtration Filtration allows you to separate an insoluble solid from a liquid The liquid is able to pass through the filter paper but the solid cannot.

  8. Crystallisation If you have a soluble solid dissolved in a liquid, you cannot separate them by filtration. You can evaporate the liquid, leaving behind the solid. This works because the solid has a much higher boiling point than the liquid

  9. Filtration and crystallisation can be used together if you have both a soluble solid and insoluble solid. For example a mixture of sand, salt and water. https://www.youtube.com/watch?v=vi_SJBnxmHo

  10. Bronze: Produce a clear, labelled diagram showing how filtration and crystallisation can be carried out. Silver: Justifywhy filtration and separation can t always be used for the same mixtures. Gold: Evaluate the methods for both filtration and crystallisation. Identify any possible mistakes that could be made and hazards when carrying them out.

  11. Chromatography Paper chromatography is used to separate mixtures of soluble substances. These are often coloured substances such as food colourings, inks, dyes or plant pigments.

  12. Chromatography Some inks dissolve more easily than others. This means they will move up the paper faster.

  13. Chromatography In chromatography there are 2 phases: Stationary phase the paper (it doesn t move) Mobile phase the solvent / liquid (it does move)

  14. Chromatography Separation by chromatography produces a chromatogram. A paper chromatogram can be used to distinguish between pure and impure substances: a pure substance produces one spot on the chromatogram an impure substance, or mixture, produces two or more spots Distance the ink moved from the pencil line Distance the solvent liquid moved from the pencil line Rf =

  15. Chromatography For each spot you can calculate the Rf value. The Rf value tells you how easy it was for that substance to dissolve and move up the paper.

  16. Exam Practice. Attempt each of the following exam questions

  17. Self Assess your answers

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