GCSE Chemistry - Paper Chromatography #63

Summary

This 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

00:00

🔍 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.

05:01

📊 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.

Keywords

💡Paper Chromatography

Paper chromatography is a method used to separate the components of a mixture based on their different affinities for the mobile and stationary phases. In the context of the video, it is used to separate different dyes in ink. The process involves applying the ink sample onto a filter paper, which is then placed in a solvent, allowing the dyes to move at different rates based on their solubility in the solvent.

💡Mobile Phase

The mobile phase in chromatography is the substance through which the sample components move. It is typically a liquid or gas, and in the video, it is the solvent used in the paper chromatography process. The mobile phase is crucial as it carries the different dyes in the ink sample up the filter paper, causing them to separate based on their varying solubilities.

💡Stationary Phase

The stationary phase is the material that the mobile phase moves through, and it is usually a solid or a very viscous liquid. In the video, the filter paper serves as the stationary phase where the ink dyes are applied and where they interact with the paper's fibers, affecting their rate of movement during the chromatography process.

💡Baseline

The baseline in paper chromatography is the line drawn near the bottom of the filter paper where the ink sample is applied. It is a reference point from which the movement of the dyes is measured. In the script, the baseline is established with a pencil before adding the sample, ensuring that the solvent does not reach this point and affect the separation process.

💡Solvent

A solvent is a substance, typically a liquid, capable of dissolving other substances. In the video, a solvent like water or ethanol is used in the paper chromatography process to dissolve the ink dyes and facilitate their movement up the filter paper. The choice of solvent can affect the separation efficiency and the resulting chromatogram.

💡Chromatogram

A chromatogram is the visual representation of the separation achieved through chromatography. It shows the pattern of spots left after the solvent has almost reached the top of the paper and the paper has dried. In the video, the chromatogram is the final result that helps identify the different substances in the ink by their distinct spots.

💡rf Value

The rf value, or Rf value, stands for the retardation factor and is a ratio used in chromatography to quantify the distance a substance travels relative to the solvent front. In the script, it is calculated as the distance traveled by the substance divided by the distance traveled by the solvent. This value is important for comparing and identifying substances in different chromatographic runs.

💡Substances

In the context of the video, substances refer to the different dyes or chemical components that make up the ink sample. These substances are separated during the paper chromatography process based on their unique properties, such as solubility in the solvent and affinity for the paper.

💡Separation

Separation in the video refers to the process by which the different dyes in the ink sample are distinguished from one another as they travel up the filter paper at different rates. This is a key aspect of paper chromatography, allowing for the identification and analysis of the components within a mixture.

💡Dyes

Dyes in the video are the pigments or substances that impart color to the ink. They are the focus of the paper chromatography experiment, as their separation on the filter paper allows for the identification of the different colors present in the ink and their individual properties.

💡Identification

Identification in the context of the video is the process of determining the nature of the substances in the ink by analyzing the resulting chromatogram. By comparing the rf values and the pattern of spots to known standards, one can identify the specific dyes or chemical components present in the ink sample.

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