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Diffusion Demonstration

March 29, 2021 By Emma Vanstone Leave a Comment

Imagine pulling a delicious cake out of an oven, the smell slowly spreads around the room and then through the house. This is diffusion! The lovely cake smelling particles move from where there are lots of them ( high concentration ) to where there are less of them ( low concentration ). Diffusion can be quite a slow process as the movement of particles is random. One very easy diffusion demonstration is to pour squash or food colouring into a glass of water and watch as the colour spreads through the glass.

Diffusion is the movement of a substance from an area of high concentration to an area of low concentration until its concentration becomes equal throughout the available space.

This video shows diffusion in action .

Diffusion Demonstration with Squash and Water

Squash or juice in water is a great demonstration of diffusion. You can see the squash starts in one area and then starts to move from areas of high squash concentration to areas of low concentration. Eventually the squash spreads throughout the whole glass and the colour becomes paler and even throughout. ​

I used food colouring in the images below to make the process easier to see.

Diffusion using food colouring and water

What is diffusion?

Diffusion is the movement of a substance from an area of high concentration to an area of low concentration.

Diffusion occurs in gases and liquids. Particles in gases and liquids move around randomly, often colliding with each other or whatever container they are in. When they collide they change direction which means eventually they spread out through the whole available space.

Examples of Diffusion

Diffusion in humans.

Oxygen diffuses from the alveoli of the lungs into red blood cells. This is because the concentration of oxygen in the alveoli is high and the concentration of oxygen in the red blood cells is low. Red blood cells have very thin cell walls which allows oxygen to diffuse easily in and out of them.

Diffusion in plants

Plants use carbon dioxide fro the air for photosynthesis. Carbon dioxide enters the leaves through small holes called stomata in the underside of the leaf. Spongy cells called mesophyll cells allow gases to diffuse easily in and out of the leaf. The stomata can open and close so the plant doesn’t lose too much water.

More diffusion demonstrations

Making a cup of tea is another great diffusion demonstration. This diffusion activity using different shaped tea bags is great fun.

Another example of movement of substances important for living things is osmosis .

Last Updated on November 3, 2021 by Emma Vanstone

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Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

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Teilchenmodell

Löslichkeit von früchtetee in wasser.

Zielsetzung

• Mit diesem Experiment lernst du, wie sich die Temperatur des Lösungsmittels auf die Löslichkeit von Stoffen auswirkt.

Hinweise zum Experiment

Damit in Chemie bzw. beim Experimentieren keine Unfälle passieren, musst du auf die Sicherheit achten. Die Sicherheit ist immer wichtig, wenn du in einem Fachraum oder Labor bist. Bitte beachte bei allen Experimenten die  Hinweise zur Sicherheit im Labor .  Die Durchführung des Experiments erfordert eine Gefährdungsbeurteilung durch die Lehrkraft.

• 3 Bechergläser
• Wasserkocher
• Thermometer
• Handy-Kamera

Chemikalien

• Teebeutel mit Früchtetee (z. B. Hibiskustee)
• Crushed Eis
• Wasser (Abb. 1)

Versuchsaufbau/Durchführung

• Gib in ein Becherglas ca. bis zur Hälfte Crushed Eis und Wasser (Abb. 2).
• Fülle in ein zweites Becherglas kaltes in ein drittes Becherglas heißes Wasser. Achte auf gleiche Füllhöhe.
• Messe in den drei Bechergläsern die Temperatur des Wassers.
• Öffne deine Kamera-App und wähle die Zeitrafferfunktion. Starte das Video.
• Gib in jedes Becherglas einen Teebeutel.
• Lasse die Bechergläser ruhig stehen und filme ca. 5 Minuten. Protokolliere deine Beobachtungen.

Führe den Versuch durch. Was kannst du beobachten? Erkläre deine Beobachtungen auf Teilchenebene.

Beobachtung

Das heiße Wasser färbt sich sehr schnell rot, das kalte Wasser färbt sich sehr viel langsamer rot. Im Eiswasser ist erst nach längerer Zeit eine schwache Rotfärbung zu sehen (Abb. 4).  

Die Wasser-Teilchen bewegen sich hin und her und stoßen dabei auf den Verbund von Farbstoff-Teilchen im Tee. Dabei trennen die Wasserteilchen einzelne Farbstoff-Teilchen ab und bilden eine Hülle um diese Teilchen.  

Mit zunehmender Temperatur bewegen sich die kleinen Teilchen immer schneller. Dadurch treffen in heißem Wasser die Wasserteilchen häufiger und schneller auf die Farbstoff-Teilchen als in kaltem Wasser und lösen die Farbstoff-Teilchen sehr schnell aus ihrem Teilchenverbund heraus. In kaltem Wasser bewegen sich die Wasserteilchen sehr viel langsamer. Deshalb dauert es auch viel länger, bis sie die Farbstoff-Teilchen aus ihrem Verbund herauslösen. 

Schreibe ein Rezept, wie du im Sommer Früchteeistee herstellen würdest. Begründe dein Vorgehen.

Zuerst heißes Wasser auf Früchteteebeutel geben und den Tee abkühlen lassen. Anschließend den Tee mit Eiswürfel weiter kühlen.   Begründung: In heißem Wasser lösen sich Farbstoffe und Aromastoffe sehr viel besser als in kaltem Wasser (Begründung s. o.). Von daher ist es sinnvoll, die Inhaltsstoffe des Tees mit heißem Wasser herauszulösen und dann den Tee abzukühlen und nicht umgekehrt. 

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Home » Articles » STEM » STEM Science » How to Demonstrate Diffusion with Hot and Cold Water

How to Demonstrate Diffusion with Hot and Cold Water

We all need some space sometimes, right that’s true down to a molecular level. molecules don’t like to stay too close together and will try to move to less crowded areas. that process is called diffusion and we will explore all about it in this simple but revealing experiment., article contents.

What is Diffusion?

Have you ever smelled your neighbor’s lunch on your way home? Or smelled someone’s perfume minutes after that person was gone? You experienced the diffusion!

Diffusion is a movement of particles from the area of high concentration to an area of low concentration. It usually occurs in liquids and gases.

Let’s get some complex-sounding terminology out of the way. When talking about diffusion, we often hear something about the concentration gradient (or electrical gradient if looking at electrons). Gradient just means a change in the quantity of a variable over some distance. In the case of concentration gradient, a variable that changes is the concentration of a substance. So we can define the concentration gradient as space over which the concentration of our substance changes.

For example, think of the situation when we spray the air freshener in the room. There is one spot where the concentration of our substance is very high (where we sprayed it initially) and in the rest of the room it is very low (nothing initially). Slowly concentration gradient is diffusing – our freshener is moving through the air. When the concentration gradient is diffused, we reach equilibrium – the state at which a substance is equally distributed throughout a space.

It’s important to note that particles never stop moving , even after the equilibrium is reached. Imagine two parts of the room divided by a line. It may seem like nothing is happening, but particles from both sides are moving back and forth. It’s just that it is an equal probability of them moving from left to right as it’s from right to left. So we can’t notice any net change.

Diffusion is a type of passive transport . That means it doesn’t require energy to start. It happens naturally, without any shaking or stirring.

There is also a facilitated diffusion which happens in the cell membranes when molecules are transported with the help of the proteins.

You may remember hearing about Osmosis and think about how is this different from it. It is actually a very similar concept. Osmosis is just a diffusion through the partially permeable membrane. We talked about it more in our Gummy Bear Osmosis Experiment so definitely check it out.

What causes Diffusion?

Do particles really want to move somewhere less crowded? Well, no, not in the way we would think of it. There is no planning around, just the probability.

All fluids are bound to the same physical laws – studied by Fluid mechanics , part of the physics. We usually think of fluids as liquids, but in fact, air and other types of gas are also fluids ! By definition , fluid is a substance that has no fixed shape and yields easily to external pressure.

Another property of the fluids is that they flow or move around. Molecules in fluids move around randomly and that causes collisions between them and makes them bounce off in different directions.

This random motion of particles in a fluid is called Brownian motion . It was named by the biologist Robert Brown who observed and described the phenomenon in 1827. While doing some experiments with pollen under the microscope, he noticed it wiggles in the water. He concluded that pollen must be alive. Even though his theory was far off, his observation was important in proving the existence of atoms and molecules.

Factors that influence Diffusion

There are several factors that influence the speed of diffusion. The first is the extent of the concentration gradient . The bigger the difference in concentration over the gradient, the faster diffusion occurs.

Another important factor is the distance over which our particles are moving. We can look at it as the size of a container. As you may imagine, with the bigger distance, diffusion is slower, since particles need to move further.

Then we have characteristics of the solvent and substance. The most notable is the mass of the substance and density of the solvent . Heavier molecules move more slowly; therefore, they diffuse more slowly. And it’s a similar case with the density of the solvent. As density increases, the rate of diffusion decreases. It’s harder to move through the denser solvent, therefore our molecules slow down.

And the last factor we will discuss is the temperature . Both heating and cooling change the kinetic energy of the particles in our substance. In the case of heating, we are increasing the kinetic energy of our particles and that makes them move a lot quicker. So the higher the temperature, the higher the diffusion rate.

We will demonstrate the diffusion of food coloring in water and observe how it’s affected by the difference in temperature. Onwards to the experiment!

Materials needed for demonstrating Diffusion

• 2 transparent glasses – Common clear glasses will do the trick. You probably have more than needed around the house. We need one for warm water and one for cold water so we can observe the difference in diffusion.
• Hot and cold water – The bigger the difference in temperature in two glasses, the bigger difference in diffusion will be observed. You can heat the water to near boiling or boiling state and use it as hot water. Use regular water from the pipe as “cold water”. That is enough difference to observe the effects of temperature on diffusion.
• Food coloring – Regular food coloring or some other colors like tempera (poster paint) will do the trick. Color is required to observe the diffusion in our solvent (water). To make it more fun, you can use 2 different colors. Like red for hot and blue for cold.

Instructions for demonstrating diffusion

We have a video on how to demonstrate diffusion at the start of the article so you can check it out if you prefer a video guide more. Or continue reading instructions below if you prefer step by step text guide.

• Take 2 transparent glasses and fill them with the water . In one glass, pour the cold water and in the other hot water. As we mentioned, near-boiling water for hot and regular temperature water from the pipe will be good to demonstrate the diffusion.
• Drop a few drops of food coloring in each cup . 3-4 drops are enough and you should not put too much food color. If you put too much, the concentration of food color will be too large and it will defuse too fast in both glasses. 
• Watch closely how the color spreads . You will notice how color diffuses faster in hot water. It will take longer to diffuse if there is more water, less food color and if the water is cooler.

What will you develop and learn

• What is diffusion and how it relates to osmosis
• Factors that influence diffusion
• What is Brownian motion
• How to conduct a science experiment
• That science is fun! 😊

If you liked this activity and are interested in more simple fun experiments, we recommend exploring all about the heat conduction . For more cool visuals made by chemistry, check out Lava lamp and Milk polarity experiment . And if you, like us, find the water fascinating, definitely read our article about many interesting properties of water .

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Real Diffusion Experiment (for Home or School)

Introduction: Real Diffusion Experiment (for Home or School)

As part of my research and my physics degrees I've been studying a lot about diffusion and diffusion-related subjects. After a while it finally hit me that I learned about diffusion before - in my highschool biology class. I thought about the experiments they showed us, and something didn't make sense. So I searched YouTube for diffusion demonstrations, and they looked pretty much the same - someone drops a bit of dye into a large water-filled beaker, and after a few minutes the entire beaker is colored.

At this point I realized how big the misconception about diffusion is! Most diffusion demos are completely wrong !

As I'll show you soon enough, diffusion on these scales takes weeks to happen! All of these demos in fact show a process called 'convection' in which the dye mixes due to currents and swirls in the liquid, not due to diffusion.

So, in this instructable I'll first try to convince you that there's something wrong with these experiments, and that we should re-evaluate how we demonstrate diffusion to student. Then, I'll show you how you can perform diffusion experiments the right way (there's more than one way, of course!). Finally, I'll discuss some of the consequences of the results, which can actually teach us a lot about the world we're living in.

My hope is that - if I convince you that the typical diffusion demos are wrong - you spread the word! Teach the ones you can! And on the other hand, if you think that I'm wrong here - I'd love to hear your opinion, see your experimental data, and talk about it!

I've been waiting to make an instructable about this subject for a while now, but I never really got to it. Finally, the science fair contest motivated me getting it done and posting this article :) I hope you like it!

I made a video about this project for those who like watching narrated videos

If you have any questions or comments, I'd love to hear all of them!

Step 1: what's wrong with typical diffusion demos.

In the diffusion demonstrations we're used to seeing, the main things that cause the dye to mix are not diffusion. It is swirls and currents in the liquid, a process called convection. Most commonly, a drop of dye is injected into a large water-filled beaker, and the audience watch as the color mixes (see the GIF I attached of such experiment I performed myself). The spread of the dye is said to be due to diffusion. However, this is not true. You can clearly see currents and swirls in the liquid (convection).

There are many things that cause the convection. First, the beakers are often wide open and so any currents in the air are transferred to the water, causing them to swirl. Next, since the top of the beaker is open, there's evaporation of water happening (see the drawing I attached). This means that the top of the water container becomes cooler than the bottom. Since cold water is slightly denser, it tends to sink, which leads to currents and swirls again. Finally, these experiments are often done with warm water in intent to show that diffusion is temperature-dependent. However, everything I just mentioned is also enhanced with the increased temperature! The difference between the beaker's temperature and the rest of the room is bigger, and so the water develops an even steeper temperature gradient, which makes everything even worse!

Diffusion, as it turns out, can be very very slow. Humans are used to seeing big things - things on the scale of a mm (1/25") are already pretty small for the human eye. However, diffusion is extremely inefficient at these sizes! Diffusion is fast and efficient only on the scale of microns and smaller, and if you follow along, you'll see exactly why!

This should not be discouraging - the fact that diffusion is slow on large scales - but quick on small scales - explains so much of the world around us, including a lot of biological phenomena, and I'll elaborate on that in the final section.

I'm not trying to say that diffusion experiments are impossible to see and demonstrate, I'm just saying that the most common form of diffusion demos is wrong! There are ways to do it right!

Step 2: Experimental Setup

We need to make sure that convection doesn't happen in our experiment. Here are the things that helped me get it done. I tried skipping some of these, but it didn't work :)

• Use a thin container. Glass test tubes or other things with similar proportions could work. These are pretty cheap, I bought mine from AliExpress.
• We should make sure that when we inject the dye, it doesn't swirl right from the start. To do that, I used salt water (5% salt) instead of tap water. This made them heavier and so the dye floated on them. It doesn't change anything for diffusion (why? you can ask your students questions like this one! let me know if you want the answer), but it helps with the initiating the experiment in a controlled manner.
• Let all of the liquids rest at room temperature before starting. If they have different temperatures, it'll cause convection.
• Inject the dye gently to the top of the container so that it floats at the top. Avoid dropping it from a distance.
• Use plastic wrap or a cork cap to seal the test tube after you initiate the experiment. This will help fight the evaporation and air currents from messing with your experiment.
• Finally, this experiment is best done in a constant environment where the temperature is pretty constant over time. If you want to film it, a good place would be inside a cabinet or a closet.

I used a dye called Fluorescein which is very common in laboratories (often used for diffusion experiments). However, food coloring or ink work perfectly fine. If it's water soluble and has a strong color, it should be fine.

Step 3: Data Capture

Capturing the data is important if we want to have a quantitative understanding of the phenomena. It will also let us see the diffusive behavior as a function of time even though things are moving slowly (see the GIF I attached - that's 48 hours!).

• You want the capture data with a nice clear background. I found that using a black paper works well, but it often depends on the type of food coloring or dye you're using.
• You also want to capture images with constant lighting and camera settings. For that reason, I kept the experiment running inside a closet with a fixed light source :) sunrise & sunset can interfere with your data.
• I found a really nice app called 'Open Camera' (thanks Orit !). It allows you to take timelapse images, set the image resolution, and fix the focus / exposure so it doesn't change automatically. You can also save the data to a google drive folder which means you can check how things are going without opening the closet and having the risk of a ruined experiment. You shouldn't take more than an image every 5-10 minutes. Nothing happens that fast anway, the experiment will probably be running for days.
• Before initiating the experiment, take an image with something of a known size. For example, taking a picture of a ruler would be useful. You'll see more about why this is needed in step 6.
• Initiate the experiment and wait. Take the time and follow the images over your google-drive folder. Try to avoid opening the closet while the experiment is running!

Step 4: Data Analysis Software - 'Tracker' (free Academic Software)

There are many ways analyze the experimental data. I found Tracker can be used in so many physics experiments that it's worth getting to know. It's available in many different languages (not only English), so young students from all over the globe can use it.

Download the Tracker software here . There's an online version but it doesn't work well.

An alternative to 'Tracker' is a software called 'ImageJ' or 'Fiji' (basically the same). It works great too, and has some advanced options too.

To start analyzing your videos, import them. Tracker accepts videos of many formats, but also sequences of images. Note that sequences of images need be named in a fixed format with a incrementing numbers. For example, Img001, Img002, Img003... are good file names (see first image)

You'll often want to rotate the image so that the direction you're interested in is horizontal. To do that, right-click the video, and press filters -> new -> rotate. Rotate the image in the desired direction (see second image).

I've also written a code python to analyze a sequence of images automatically , more about that (file included) in the data-analysis step.

Step 5: Calibrate Pixels to Physical Units

We took images or videos of the real world, but the software has no way of knowing what we're looking at, what's it's size, and how often images were taken. We need to calibrate both space (distances) and time to physical units. You'll need to do this even if you analyze the data in a different software.

To Convert Pixels to Distance Units (GIF #1):

• Select the 'calibration tools' from the toolbar.
• Add a new calibration stick.
• Align it along a known distance. For example, I took a picture of a ruler.
• Calibrate the measured distance. I'm using meters, but you can change to any units you like by pressing the 'Coordinate system' tab -> 'Units...' and setting your preferred system of units.

To Calibrate Time (GIF #2):

• Right-click the video (anywhere on the screen), and press 'Clip Settings'
• Set the frame rate (FPS) or the time interval between images in a sequence (dt). I analyzed images that were taken every 30 minutes, so I set 'dt' to 1800 seconds.

You can set the coordinate system (where x, y = 0) and its orientation on the screen by pressing the coordinate axes tool in the toolbar (see third image).

That's it, from this point on your measurements will be in physical units.

Step 6: Measure the Diffusion Process Over Time

I'm including here 3 different types of analysis. I'll list them in order of complexity, the first one being the easiest one to use but also the least accurate, and the last one being the most complex and accurate method of analysis.

First Method - 'By Eye' (GIF #1):

The food coloring (or whatever ink or chemical you're using as dye) colors the water. We can look for the point where it is no longer visible, and track it's position over time.

• In the 'Tracker' software, press 'Track' -> 'New' -> 'Point Mass'.
• Hold 'Shift' and use the mouse choose the point at which the paint is not longer visible. Each time you click, the software will move on to the next frame.
• You can go back and edit points if you like. You can also decide to skip multiple frames in each click by changing the 'step size' at the bottom. This can be useful especially when things change slowly.
• Keep going until you went through all of the video / image sequence.

Second Method - Intensity Profile (GIF #2):

The previous method lacks some accuracy. 'The point where the dye is not longer visible' is not well defined, and depends on the person analyzing the data. A more robust way of analyzing the data is by looking at the intensity profile of the image. Brighter regions have higher intensity than darker regions. We can measure in Tracker as well.

• Add a new Track of a 'Line Profile' type.
• Use Shift to place it along the direction of the diffusion process.
• A window will open on the right side of the screen showing the intensity as a function of distance. Define a point in the intensity profile that you want to track. For example, 'the point where intensity is equal to 50'.
• Measure it's position over time. You'll need to write down the time and position of each point manually (you can write it into an Excel sheet). Students can do this in pairs to save time. I realize this can be time consuming if you go through all of the captured frames, but analyzing about 20-30 frames should be plenty! Adjust the 'step size' so you skip through more than one image at a time.

Third Method (GIF #3):

This method is basically an upgrade of the previous one. I wrote a python code that analyzes the data automatically. It runs through each image and measures the intensity profile along a selected region. It does a few extra things like removing the background noise and such. Also, I used a green dye so it analyzes the green channel of an RGB image, but you can make a small modification to the code to analyze other colors or all of them combined.

• Run the code and analyze your images.
• You'll end up with all of the intensity profiles. All that is left is to track a selected point along the profile. Say, 50 gray points above the background. Define a threshold that would work for your images.
• For each profile, calculate it's distance from the threshold, that is: abs(profile - threshold). The smallest value of this vector will be the point where the profile is equal to the intensity threshold you've chosen, so the easiest way to find it is by looking for: min(abs(profile - threshold). I've attached MATLAB code that does all of this, plots the profiles, and saves them as images.

Attachments

Step 7: how fast are things moving.

Now that we have tracked the diffusion process over time, we can start the final part of the experiment. In this part we will try to answer questions about the rate at which diffusion occurs.

By looking at the images we've aquired we already have an intuitive feeling for it - diffusion starts off pretty fast, but then, as time passes, it slows down. My experiment was running for 48 hours, and the test tube was far from well mixed. The typical distance the dye I used propagated was about 1cm (less than 1/2"). This is very slow, and very typical for diffusion in water!

I made a GIF of the time dependence of the intensity profile for the first 48 hours of the experiment. We can see that the profile changes very rapidly at first, but then it slows down. This is what we see in the images too, so that's a good sign the analysis works :) I then defined the point where the front of the intensity profile reaches a value of 50 gray points above the background intensity, and marked it with an orange circle on each of the profiles (see third method in the previous step for details). I called this point 'x_D' (D for diffusion).

Finally, I plotted x_D as a function of time (see the graph I attached). x_D is shown with orange markers. There's also a blue line on the graph. This graph describes a theoretical fit to the data. Diffusion has a very precise physical formulation which matches reality to very high accuracy. It suggests that diffusion should occur at a rate that scales as the square root of time. In other words, x_D should scale as: x_D ~ sqrt(D * t), where 'D' is the diffusion coefficient of the dye in water and 't' is time. So, I tried to fit the x_D data to a function of the form x_D = sqrt(D * t). The fit is very good, so it seems that diffusion does scale as the square root of time, as expected! I could also use the fitted function to get an estimate for the diffusion coefficient, and found that it is of the order of 4 * 10^-6 [cm^2/sec]. This is very close to the real value of the dye I used (5.5 * 10^-6 [cm^2/sec]). This difference was expected since I could have defined x_D slightly differently and end up with other results. Measuring the exact diffusion coefficient takes a little more effort than what I did here, but for an estimate and order-of-magnitudes this is perfectly fine.

Step 8: Conclusions

We saw that x_D scales as x_D ~ sqrt(D * t). We can now ask, if we wanted for the dye to reach a point x_D away from the source of the dye, how long should we wait? This is answered by inverting the equation: t_D = (x_D ^2)/D. This seems mondane - nothing special, right? But this equaion dictates so much in biology and life. For example, have you ever wondered why cells are small? Why don't we see huge elephant-sized cells? One of the main reasons for that is that cells depend on diffusion to obtain nutrients. If cells were too big, diffusion would become inefficient. Using the diffusion coefficient we found, we see that diffusion will take about 40 minutes to pass just 1mm (1/25.4"), but it would take less than a second to pass a distance of 10 microns , a typical distance to travel when thinking about cells. For instance, when you exercise, your muscle cells need constant supply of oxygen. If the cells were too big (1mm sounds small, right?), diffusion would become inefficient and the oxygen supply wouldn't reach the inside of the cells fast enough. [the sizes-GIF was created base on Learn Genetics ]

To conclude,

We saw that diffusion experiments need careful attention and a lot of patience. I found that the best way to demonstrate this phenomenon is by capturing a video. You can do that with the students if you want to take this into the class-room. Another option would be to initiate the experiment on one day and looking at the results the next day. You'll see the dye has started to mix into the water.

On large scales, diffusion takes a very long time (over a mm or 1/25.4 of an inch is already considered large!), but on very small scales, such as the sizes of cells (a few microns), diffusion is a very efficient way to move things around. This explains a lot about biological processes and other physical phenomena. I think that once you develop intuition for the process and its time-scales, you can appreciate so many things about the world around us.

I hope you found this topic as interesting as I find it! And if you're in the world of teaching, I hope you spread the word! There's a huge misconception about diffusion due to wrongful demonstrations, and it's our job to make things right :)

If you like my instructable and want to see more, you're welcome

To visit my instructables page and my website.

By the way, if you want to support my projects - subscribing to my new YouTube channel is currently the best way to do that! :)

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Diffusion Demonstration

By Fergy on September 16, 2016 1

This activity can either be done as a student inquiry or teacher demonstration. In either case, a preliminary and follow-up discussion can be used to stimulate thinking and reinforce concepts taught in the unit.

Materials needed: • 2 tea bags • 2 transparent mugs or glasses • cold water – ice cold water if possible • a kettle

The Activity: 1. Have your students draw this chart.

2. Ask your students what they think will happen when one tea bag is put into hot water and another into cold water? Have them write it down in the ‘My Opinion’ column including why they think so. 3. Have your students share their answers with the person beside them. Each student should then write the combined opinion in the ‘Group Opinion’ column as they did before. 4. Lastly, have each group share their results with another group and write the consensus opinion in the ‘Shared Opinion’ column. 5. Perform the demonstration by placing 1 tea bag into a cup of cold water (the colder the better – use ice cubes if possible) and 1 tea bag into a cup of boiling water.

Time-Lapse 8X Speed

6. Have your students complete the row ‘Describe what happened’ 7. Explain what occurred.

Explanation: First some simple thermodynamics: You know in those airplane or space movies where a door is opened and people get sucked out? Well, that doesn’t really happen, not like that anyways. Yes, air does move from inside to outside but there isn’t the massive suction effect. Prior to that door being opened, molecules of air continually collide with the door but do so in a random manner. When the door is opened, there’s simply nothing stopping their motion so any molecule that would have collided with the door, simply leaves the room. There’s a net movement of molecules from inside to outside because there are more molecules inside therefore, there’s a greater chance of one of them moving through the door than a similar molecule moving from outside to inside. After a short time (shown in the movies as that suction effect I already mentioned), there is an equal number of molecules inside and outside. The molecules are still moving and passing through the door, however, now the number of molecules that pass from inside to outside, is the same as those that move from outside to inside

The molecules in the left diagram will experience a net movement from left to right. The diagram on the right shows an equal distribution and therefore, there will be no net movement.

Diffusion is just like that. It’s the movement of a substance from an area of high to low concentration due to the random motion of molecules in a container. If we put a thermometer inside a liquid, we see the reading as how hot or cold the liquid is. However, what we are really finding out is how quickly the objects inside the liquid are moving. A higher temperature means greater motion. A lower temperature means less motion. Absolute zero (0° Kelvin) is the point where a molecule stops its motion entirely. However, this number is only theoretical as we’ve never experienced an absolute zero situation. Even space is approximately 2.7° Kelvin or -270.45° Celsius. Back to our door example. Since temperature is motion and we know that a molecule’s motion is random, it can be understood that if we increase the air temperature, our molecules are going to move faster and therefore, will randomly collide with our open door more often. Liquids are no different. If we increase the temperature of the liquid, the molecules inside will gain energy and move faster. The faster they move, the more quickly they will spread out into their container. This is what happens when you put a tea bag into cold and hot water.

Tea Bag In Cold Water: In the cold water, the molecules of the tea bag don’t have as much energy and therefore, don’t move as fast. It takes them a long time to spread evenly throughout the water.

Tea Bag In Hot Water: Alternatively, in hot water, the molecules of the tea bag have a lot more energy and therefore, spread into the surrounding water quickly.

After 10 minutes of diffusion

8. Have your students complete the last row using the information you provide in the explanation.

That’s it. Please let me know what you think in the comments.

Devon – Teach With Fergy

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July 1, 2017 at 3:04 pm

I like this. It will be easier to clean up over using jaw breakers! I haven’t really thought about using hot water before, but I will this next school year.

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Diffusion Lab Experiments

Chemistry Projects for Diffusion in Liquids

Diffusion is a physical phenomenon that occurs everywhere, and we barely notice it or understand how it works. However, a few simple experiments can reveal the mysterious nature of this simple phenomenon.

Preparing for the Experiments

Taking some time to set these experiments up can make your life much easier and allow you to better focus on the results of the experiment. First, grab three glass beakers. Make sure the beakers are transparent. Fill a large pitcher of water or do your experiments near a tap. Also, get three different colors of food dye. To be very precise, you will want a thermometer, but you don't need one unless you are picky. Also have a timer or stopwatch. Finally, make sure you have some way of heating or cooling the water before you start.

Observing Simple Diffusion

This is by far the most simple experiment. However, you'll have to know beforehand that diffusion is the propagation of a substance from an area of high concentration to an area of low concentration, the purpose of which is to reach a state of equilibrium, or a state in which there is an even concentration of a substance across a medium. Now that you know what diffusion is, you need to see it yourself. Take a beaker and fill it with water to around three-quarters. Now, simply pour a small amount of food dye into the water. Observe whether the dye diffuses from a high concentration to a low concentration and try to observe where those two states occur. This will give you a good idea of what diffusion looks like.

Testing How Temperature Affects Diffusion

Now, all your preparation will come to fruition. Fill all three beakers with tap water to around three-quarters filled. The tap water should be around 50 to 60 degrees Fahrenheit, or as close as you can get. Now, cool one beaker by placing it in a refrigerator or similar device. Heat the other beaker with a stove, microwave or, if you have one, a Bunsen burner. You can make the temperatures of all thee beakers whatever you want, really. The important thing is that one is around 20 degrees hotter than another, which is around 20 degrees hotter than another. Finally, put one color of dye in each beaker and observe the diffusion. Your objective in this experiment should be to measure how fast each dye diffuses through each temperature of water. Make sure to write down how fast the dye diffuses in each temperature of water.

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David Scott has been a firefighter for the Seattle Fire Department's Technical Rescue Team for almost 20 years. He has been writing primarily since 2005, but did author the book, "The White River Ranger District Trail Guide" in 1988. In addition to his work for Demand Studios, Scott spends much of his time writing poetry and a novel.

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Top 5 Experiments on Diffusion (With Diagram)

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The following points highlight the top five experiments on diffusion. The experiments are: 1. Diffusion of S olid in Liquid 2. Diffusion of Liquid in Liquid 3. Diffusion of Gas in Gas 4. Comparative Rates of Diffusion of Different Solutes 5. Comparative rates of diffu­sion through different media.

Experiment # 1

Diffusion of s olid in liquid:.

Experiment:

A beaker is almost filled with water. Some crystals of CuSO 4 or KMnO 4 are dropped carefully without disturbing water and is left as such for some time.

Observation:

The water is uniformly coloured, blue in case of CuSO 4 and pink in case of KMnO 4 .

The molecules of the chemicals diffuse gradually from higher concentration to lower concentration and are uniformly distributed after some time. Here, CuSO 4 or KMnO 4 diffuses independently of water and at the same time water diffuses independently of the chemicals.

Experiment # 2

Diffusion of liquid in liquid:.

Two test tubes are taken. To one 30 rim depth of chloroform and to the other 4 mm depth of water are added. Now to the first test tube 4 mm depth of water and to the other 30 mm depth of ether are added (both chloroform and ether form the upper layer).

Ether must be added carefully to avoid disturbance of water. The tubes are stoppered tightly with corks. The position of liquid layers in each test tube is marked and their thickness measured.

The tubes are set aside for some time and the thickness of the liquids in each test tube is recorded at different intervals.

The rate of diffusion of ether is faster than that of chloroform into water as indicated by their respective volumes.

The rate of diffusion is inversely proportional (approxi­mately) to the square root of density of the substance. Substances having higher molecular weights show slower diffusion rates than those having lower molecular weights.

In the present experiment ether (C 2 H 5 -O-G 2 H 5 , J mol. wt. 74) diffuses faster into water than chloroform (CHCI 3 , mol. wt. 119.5). This ratio (74: 119-5) is known as diffusively or coefficient of diffusion.

Experiment # 3

Diffusion of gas in gas:.

One gas jar is filled with CO 2 (either by laboratory method: CaCO 3 + HCL, or by allowing living plant tissue to respire in a closed jar). Another jar is similarly filled with O 2 (either by laboratory method: MnO 2 + KClO 2 , or by allowing green plant tissue to photosynthesize in a dosed jar). The gases may be tested with glowing match stick.

The oxygen jar is then inverted over the mouth of the carbon dioxide jar and made air-tight with grease. It is then allowed to remain for some time. The jars are carefully removed and tested with glowing match stick.

The glowing match sticks flared up in both the jars.

The diffusion of CO 2 and O 2 takes place in both the jars until finally the concentrations are same in both of them making a mixture of CO 2 and O 2 . Hence the glowing match sticks flared up in both the jars.

Experiment # 4

Comparative rates of diffusion of different solutes:.

3.2gm of agar-agar is completely dissolved in 200 ml of boiling water and when partially cooled, 30 drops of methyl red solution and a little of 0.1 N NaOH are added to give an alkaline yellow colour. 3 test tubes are filled three-fourth full with agar mixture and allowed to set.

The agar is covered with 4 ml portion of the following solutions, stoppered tightly and kept in a cool place:

(a) 4 ml of 0-4% methylene blue,

(b) 4 ml of 0.05 N HCl, and (4.2 ml of 0.1ml HCL plus 2 ml of 0-4% methylene blue.

The diffusion of various solutes is recorded in millimeters after 4 hours. The top of the gel should be marked before the above solutions are added.

The rate of diffusion of HCL alone (tube b) is faster compared to the combination of methylene blue and HCl (tube c) and minimum in case of methylene blue alone (tube a).

Different substances like gases, liquids and solutes can diffuse simultaneously and independently at different rates in the same place without interfering each other.

HCL being gaseous in nature and of lower molecular weight can diffuse much faster than methylene blue which is a dye of higher molecular weight having an adsorptive property. Hence in combination, these; two substances diffuse more readily than methylene blue alone.

Experiment # 5

Comparative rates of diffu­sion through different media:.