Changes of State - Part 1 Materials: - A glass of water A stove/hotplate Small muffin tin or 3 small heatproof dishes A pot or pan that can contain the tin About 3 grams each of wax, chocolate, and butter. A cup of Ice in a small pot A thermometer (oC if possible) States of Matter and Particles → Pour yourself a glass of water. While you drink it, think about what water is and about the particles it is made of. → Make a list of all that you know about water. Did you include the following in your list? Water is matter, made of particles that are tiny and move around, is a liquid at room temperature. Did you include anything else? Then email me a photo of your list. Different Matter, Different Particles Some changes in matter cause the particles themselves to change. These are called chemical changes and they transform one matter into another. When baking soda reacts with vinegar, both of them change: sodium bicarbonate + acetic acid → carbon dioxide + water + sodium acetate (baking soda) (vinegar) Each of the resulting materials is a different kind of matter and has different particles! Hands-on: Let It Melt → Place the wax, butter, and chocolate in separate wells in the muffin tin, or in separate small heat-proof containers. → Take a pot or pan, put a small layer of water in it and place the muffin tin in it. → Write down what you think will happen when you place the pot on the stove. Will all of these materials react in the same way, at the same time? Which one will melt first? → Now ask for an adult’s help and place the pot over low heat. Observe what happens and take notes. You probably now have three nice puddles of matter. → Once all three materials melted, ask an adult to help you carefully get the muffin tin out of the hot water and place it where it can safely cool down. Do Changes of State Change the Particles? What do you predict will happen when the puddles cool down? Write down your prediction. → You are now going to wait until the matter cools down completely. Give it some time, perhaps go for a short walk or read a chapter in your book, and then come back here. What happened? Is the matter no longer liquid? When all the matter hardens again it means it solidifies, or becomes solid. But what happened to the particles? It is probably now in a different shape than it was before, but did the butter go back to being butter? Wax is still wax? Is chocolate back to being chocolate? (It may look a bit discolored. That has to do with the way it solidifies. We will come back to that in a later unit). The fact that all of these things were able to stay what they were, tells you that the particles of the matter themselves did not change. When matter melts (changes from solid to liquid), freezes (changes from liquid to solid), evaporates (changes from liquid to gas), or condensates (gas to liquid), the matter’s particles stay the same, so it does not change into another kind of matter. These changes are called phase changes of matter. Since the particles themselves do not change, matter can go back and forth in between these states. If you are not familiar with the terms for each of the changes, watch this. What Determines the State of Matter? What causes state changes? Why is it that at room temperature, olive oil is liquid, but coconut oil is solid? This is what you will explore in this lesson and the next one. We will use water as an example of matter, since it can exist in all three states at temperatures that you experience in your daily life. Hands-on: Phases Changes of Water → Create a table in which you will be recording data over the next 20-25 minutes. It should be similar to this one, just with more rows: Time (minutes) Temp (oC) Observations 0 1 2 ... → Place about two cups of ice and a small amount of water in a pot. → Over the next 20-25 minutes, you will heat the ice / water and record the temperature every minute. Make sure to stir the water regularly, especially just before a temperature reading. When measuring the temperature, make sure the thermometer does not touch the pot itself, only the water. Don’t start yet. There are a few things to which you should pay attention. You will record the temperature in the table, and use the ‘observations’ column to note the following events: - All ice is melted The first noticeable steam (water vapor) appears Bubbles start to form from the center of the water Full Boil. You will know the water is in full boil when all the water in the pot is involved in the bubbling and there is a lot of steam (see photo) → With an adult’s help, turn on the stove or hot plate. Set the temperature to ‘Medium’ or a little above that. → Start watching the time. You should record your first temperature now, in the 0 minute row. → Keep recording the temperature for 3 minutes after the water is at full boil. → Be sure to turn off the stove when you are done recording your data! → While you let the water cool so you can clean up, write down any further questions or thoughts you have relating to what you just observed. Changes of State - Part 2 In this activity, you will analyze the results from part 1. You can complete this part on another day if you prefer. Materials: - Your notes from Week 3, Day 2 - Graph paper (you can print the one attached to today’s lesson) - Pencil - Ruler Have You Seen These? You learned before that every matter can exist in all three states of matter. But have you seen all of those states for all kinds of matter? For example, I have seen solid and liquid chocolate, but not gas. Create a list of at least 5 kinds of matter and for each try to recall if you have ever seen them in the different states. Arrange your list in a table like this one. Solid Liquid Gas Water ✓ ✓ ✓ Chocolate ✓ ✓ Analyzing Your Data Scientists often find it useful to organize their data in a graph. Continuous data, like you collected yesterday, is often presented as a line graph. If you are not familiar with line graphs, please watch this video before you continue. Set Up Your Graph → On your graphing paper, draw a horizontal line for the time, close to the bottom of the page. → On the left side, draw a vertical line for the temperature → Add a label to each of these axes, including the units of measurement → Look at the range of your data and mark your axes accordingly. Time goes from 0 to about 24. The temperature should start at 0 and go above the highest measured value. Plot Your Data Once your axes are ready, mark the data points based on what you recorded yesterday, then connect the dots. If this is your first time creating a graph, look at the example below before completing yours. The actual temperatures may be different, but it should be very similar. Analyzing the Graph → Look at the observations you noted in Part 1 and mark on your graph the following times: - when all the ice melted - when steam was noticeable. → What do you notice about the shape of the graph? Does the temperature continuously climb up, or are there areas where the graph stays flat? Such an area is called a plateau. → Can you see a connection between the plateau on the graph and the time when ice turns into liquid, or liquid becomes gas? Have you ever watched food coloring as it diffuses in hot and cold water? If not, you should try it. Simply take a glass of cold water and a glass of hot water, and add a drop of food coloring into each. Why does the coloring diffuse faster through the hot water? When we heat up matter, the particles have more energy and they start to move faster. In a solid, the particles have been vibrating in place, since they are strongly joined together. As they gain more energy, they will start moving so much that their movement will overcome the force holding them together. Once the particles are free to move around, the matter is no longer solid, but a liquid. A similar process would change liquid into gas. Here is a video that shows that. Back to Analyzing Your Graph Look at your graph again. Is the plateau just before a change of state? → What do you think happens during this time, when you kept heating the matter, but the temperature did not rise? This was the time when the energy was going into further separating the particles from each other. Once there was enough energy, the state of matter changed. The temperature at which matter changes from solid to liquid is called the melting point. Melting and Boiling Points of Water → On your graph, find the melting point of water. What was the temperature? → Note that it is also the freezing point of water. If you were to start with liquid water and were cooling them down, ice would start forming at 0oC (32oF). Write it in your notebook. The temperature at which matter changes from liquid to gas is called the boiling point. → On your graph, find the boiling point of water. What was the temperature? → The scientifically accepted boiling point of water is 100oC (212oF). Write it in your notebook. Melting and Boiling Points of Various Matters Based on what you saw at the beginning of this lesson, when you melted the wax, chocolate and butter, do you think all matter has the same melting point? Since you saw them melting at different time, it would make sense to assume they each have a different melting point. → Plan your own investigation, to find the melting points of wax, chocolate, and butter. Make sure to ask an adult for help and execute your plan. Then do some research to find the actual melting points of these materials and compare your results to those. Your results may vary depending on the specific wax, chocolate, and butter you use, but they should be close. What Did You Learn Today? ● Increasing the temperature of matter gives its particles more energy ● In between states, some of that energy goes into separating the particles from each other so the temperature does not rise as much ● Different kinds of matter in have different melting and boiling points, some of which are very hot or very cold, so we do not observe all matter in all states. ● Analyzing data often includes presenting it in ways that helps us notice how the data changes, such as line graphs.
