GCSE Chemistry - Paper Chromatography #63
Summary
TLDRThis video delves into the technique of paper chromatography, a method for separating substances within a mixture. It explains the process step-by-step, from drawing a baseline on filter paper to applying ink and observing the solvent's rise. The video clarifies the roles of the mobile and stationary phases, key to the separation of different dyes at varying rates. It also teaches how to calculate the rf value, a ratio indicating a substance's movement relative to the solvent. The importance of consistent experimental conditions for reliable rf values is highlighted, making it an informative guide for identifying chemicals through chromatography.
Takeaways
- 📚 Paper chromatography is an analytical technique used to separate substances in a mixture for identification.
- 📏 The process involves drawing a baseline on filter paper and applying ink sample to it.
- 🧪 A beaker is filled with a shallow amount of solvent, such as water or ethanol, for the chromatography.
- 💧 The filter paper is placed in the beaker without submerging the baseline and ink spot, allowing the solvent to rise.
- 🔄 Different dyes in the ink dissolve in the solvent and move at varying rates, leading to their separation.
- 🚫 Chemicals not soluble in the solvent will not move and remain on the baseline.
- 📈 The rate at which dyes move is determined by their solubility in the solvent and interaction with the paper.
- 📊 The chromatogram, a pattern of spots left after the solvent dries, represents the separated substances.
- 🔍 The mobile phase is the substance that molecules move in, while the stationary phase is where they don't, affecting their movement.
- 📐 The 'Rf' value is a ratio calculated to compare the movement of substances relative to the solvent's movement.
- 🔬 Rf values are used to identify substances by comparing them to data from experiments with the same phases.
- 🌟 The Rf value can vary with different solvents or papers, emphasizing the importance of consistent experimental conditions.
Q & A
What is the main purpose of paper chromatography?
-The main purpose of paper chromatography is to separate different substances in a mixture so that they can be identified.
What is the first step in conducting paper chromatography?
-The first step is to take a piece of filter paper and use a pencil to draw a line near the bottom, known as the baseline.
What is the role of the pencil line in paper chromatography?
-The pencil line serves as the baseline where the sample of ink is applied and is crucial for the separation process.
Why is it important not to submerge the pencil line and ink spot in the solvent?
-It's important to avoid submerging the pencil line and ink spot to ensure that the solvent only moves up the paper by capillary action, allowing for proper separation of the substances.
What is the mobile phase in the context of paper chromatography?
-The mobile phase in paper chromatography is the substance that the molecules can move in, which is typically the solvent used in the experiment.
What is the stationary phase in paper chromatography?
-The stationary phase is the substance or material that the molecules can't move in, which in the case of paper chromatography is the filter paper itself.
How do different dyes in ink separate during paper chromatography?
-Different dyes separate because they travel up the paper at different rates due to their varying solubility in the solvent and affinity for the paper.
What happens to substances that are not soluble in the solvent during paper chromatography?
-Substances that are not soluble in the solvent will not dissolve and move up the paper, instead, they remain on the baseline.
What is a chromatogram and how is it formed?
-A chromatogram is the pattern of spots left after the solvent has almost reached the top of the paper and the paper is dried, representing the separated substances.
What is the rf value and how is it calculated?
-The rf value is a ratio that represents the distance traveled by the substance divided by the distance traveled by the solvent, used to compare the movement of different substances in a chromatogram.
Why is it necessary to consider the solvent and paper type when comparing rf values?
-The solvent and paper type are necessary to consider because changing these elements can alter the mobile or stationary phase, thus affecting the rf value and the appearance of the chromatogram.
Outlines
🔍 Introduction to Paper Chromatography
This paragraph introduces the concept of paper chromatography, an analytical technique used to separate substances within a mixture for identification. The process involves using a filter paper with a baseline drawn near the bottom, adding ink samples, and allowing a solvent to move up the paper, causing different dyes to separate due to varying solubility rates. The importance of not submerging the baseline and ink spot is emphasized, and the use of a lid to prevent solvent evaporation is suggested. The paragraph concludes with the observation that different dyes travel at different rates, resulting in a chromatogram once the solvent has almost reached the top and the paper is left to dry.
📊 Understanding Mobile and Stationary Phases in Chromatography
This paragraph delves into the theory behind paper chromatography, explaining the roles of the mobile and stationary phases. The mobile phase, in this case, the solvent, is where molecules can move freely, while the stationary phase, the filter paper, is where molecules bind and do not move. The rate at which different chemicals move up the paper is determined by their solubility in the solvent and their affinity for the paper. The paragraph also introduces the concept of the 'Rf value', a ratio calculated to compare the distance a substance travels to the distance the solvent travels, which is used to identify substances by comparing these values to a data book. The Rf value can vary with different solvents or paper types, highlighting the importance of consistent experimental conditions for accurate identification.
Mindmap
Keywords
💡Paper Chromatography
💡Mobile Phase
💡Stationary Phase
💡Baseline
💡Solvent
💡Chromatogram
💡rf Value
💡Substances
💡Separation
💡Dyes
💡Identification
Highlights
The video discusses paper chromatography, an analytical technique for separating substances in a mixture.
Paper chromatography is particularly useful for separating different dyes in ink.
The process begins with drawing a baseline on a piece of filter paper and adding a sample of ink.
A beaker is filled with a shallow amount of solvent, such as water or ethanol, for the chromatography setup.
The filter paper is placed into the solvent without submerging the baseline and ink spot.
A lid is recommended to prevent solvent evaporation during the experiment.
Different dyes in the ink dissolve in the solvent and move up the paper at varying rates, leading to separation.
Chemicals that are not soluble in the solvent remain on the baseline.
The pattern of separated spots after the solvent dries is called a chromatogram.
The mobile phase is the substance in which molecules move, in this case, the solvent.
The stationary phase is the material that molecules cannot move through, here represented by the paper.
Chemicals move up the paper based on their solubility in the solvent and attraction to the paper.
The rf value is a ratio calculated to compare the movement of substances relative to the solvent.
The rf value is dependent on the properties of the substance and the experimental conditions.
A pure substance will not separate but show a single spot on the chromatogram with a specific rf value.
Changing the solvent or paper type can alter the chromatogram and the rf value.
Chemists use rf values in data books to identify chemicals, considering the solvent and paper type used.
The video concludes with an invitation for viewers to like and subscribe for more content.
Transcripts
in today's video we're going to talk
about paper chromatography
we'll take a look at how it's done
explain the theory behind it like what
the mobile and stationary phases mean
and also show you how to calculate rf
values
now chromatography is a general
analytical technique used to separate
the different substances in a mixture so
that we can then identify them
and there are actually lots of different
types of chromatography
but the one you need to know about is
paper chromatography
which can be used to separate the
different dyes in an ink
the first step is to take a piece of
filter paper and use a pencil to draw a
line near the bottom of the sheet
which we call our baseline
next you want to add your sample of ink
which you think might contain lots of
different substances to the pencil line
then we need to find a beaker and fill
it with a shallow amount of solvent like
water or ethanol
we are now ready to start and we can
place the filter vapor into the solvent
but importantly we have to make sure
that we don't submerge our pencil line
and our spot of ink
which is why we made our solvent shallow
and if you're being careful you should
really place a lid on top to stop the
solvent from evaporating
then we just wait for the solvent to
seep up the paper
and as it does so the different dyes
that make up our ring will dissolve in
the solvent and move up with it
what makes this interesting though is
that each of the different dyes will
travel up the paper at different rates
and so they'll end up separating out
which tells us that each one must be a
different substance
so we've basically separated out the
different substances
however if any of our chemicals aren't
soluble in that solvent then they won't
be able to dissolve and move up the
paper
so they'll just stay on the baseline
once the solvent has almost reached the
top of the paper
we take it out
and leave it to dry
and the pattern of spots that we have
left is called a chromatogram
now to explain why the different
chemicals move up the filter paper at
different rates you need to use a couple
of weird terms
the mobile phase and the stationary
phase
what makes these things odd is they
don't want to think of these phases as
periods of time but rather as types of
substances
the mobile phase is a substance that the
molecules can move in
it's always a liquid or a gas
and in our paper chromatography it would
be the solvent that we used
meanwhile the stationary phase is a
substance or material that the molecules
can't move in
so usually a solid or sometimes a really
thick liquid
but for us here it would be our paper
during the chromatography experiment the
different chemicals in our sample of
will constantly change between the
mobile and stationary phases
dissolving in the solvent
moving a little bit
and then binding to the paper
over and over again
and so overall how much time they spend
in each of these two phases is going to
determine how fast they move up the
paper
with the chemicals that are more soluble
in the solvent spending more time in the
mobile phase and therefore moving faster
and those that are less soluble
or more attracted to the paper spending
more time in the stationary phase and so
moving more slowly
so if you think about it how far each of
the chemicals travels
is dependent on the properties of that
substance
and if we do the same experiment again
our chromatogram would look the same
this means that if we measure how far
each substance moves we can compare
those values to a data book
and identify which type of chemical it
must have been
how far each of the chemicals moves
though is also going to depend on how
long we leave the experiment
so instead of comparing the actual
distance we instead calculate a ratio
called the rf value
which is equal to the distance travelled
by the substance
divided by the distance travelled by the
solvent
so if this pink substance had traveled
six centimeters from the baseline
and the solvent had traveled 10
centimeters
then our rf value would be 6 divided by
10
so 0.6
one of the important things to
appreciate with chromatography
is that when we do chromatography with a
pure substance
so a substance with only one type of
chemical in it
then it won't separate out at all
or just get a single spot on our
chromatogram for which we can calculate
a specific rf value
however if we did the experiment again
with the same substance but a different
solvent or a different type of paper
then the chromatogram might look
different
and our rf value would be different too
because we have changed the mobile or
stationary phase
so when a chemist looks up an rf value
in a data book
they'd have to take into account which
solvent the experiment was done in and
what type of paper was used
anyway that's all for today so hope you
enjoyed this video
if you did then please give us a like
and subscribe
otherwise we'll see you next time
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