Indicators are chemicals that show what type of chemical reaction occurred. I decided to have some fun with some pH indicators--chemicals that signify if a solution is acidic or basic. In the video, 3 different pH indicators, bromothymol blue, phenol red, and phenolphthalein (and ammonia) are used. The solutions are in long plastic pipes whereupon Alka Seltzer tablets are dropped. The Alka Seltzer tablets react with the water to produce carbon dioxide gas. The carbon dioxide dissolves in water creating carbonic acid and thus making the solution more acidic. The color of the solution changes as a result. Later ammonia, a base, is added to show how the color changes when the solution turns basic.
]]>Crystals are solids that are formed from regular repeating patterns of molecules. One of the most spectacular crystal formations is sodium acetate. I made sodium acetate by using a procedure from instructables. It was interesting, but very time consuming, so purchasing a bottle of it maybe a better way to go. When sodium acetate, CH3–COO– Na+, is dissolved in a little water, the oppositely charged ions dissociate. If left undisturbed and cooled, the ions do not form crystals and the sodium acetate remains a liquid, far below its melting point. If disturbed, or a tiny sodium acetate crystal is introduced into the solution, the oppositely charged ions (CH3–COO– and Na+) form a solid crytal structure quickly. The process is exothermic, releasing heat energy, which explains why this process is commonly referred to as "hot ice".
]]>A major standard our students have to learn is the difference between elements and compounds. Compounds are substances that are made of two or more elements bonded together. The elements that comprise a compound have different properties when they are bonded together than when they are separated. Students have great difficulty with this. I introduce the unit by doing a simple activity on mixtures. Educational Innovations sells a simple Mixture Separation Challenge kit. Students are first forced to separate the mixture into 3 groups. Students usually use the simplest property of color to do it. There are other properties such as relative density or optical properties (opaqueness, transparency, etc.). The main idea is that the substances can be separated by their properties, because those properties do not change when forming a mixture, unlike when a compound is formed.
]]>I found a new way to teach the conservation of mass/matter this past year. Previously I taught it by having steel wool (iron) react with oxygen. Since our periods are shorter this year, I couldn't really do that reaction anymore. Now students mix heavy whipping cream and vinegar in an open system. The vinegar reacts with the casein proteins in the heavy whipping cream to form a solid cheese-like substance (basically it is cheese). It's not a very glamourous reaction, but is also a way to teach students about precipitation. Students have a difficult time understanding the concept of two liquids reacting to make a solid. This is a simple way for students to visualize that type of chemical change.
]]>State testing is late in the school year which means that we get to spend only about two to three days on our last unit, astronomy. Luckily this year we have what's called a science reading enrichment period. It allows us to cover more in depth some of the concepts that we don't usually have time to do. This past couple of weeks, we got to cover some astronomy. In the last few years, students have been asking me numerous times two questions: "Why isn't Pluto a planet anymore?", and "Did you hear about the 10th planet?" Normally I would quickly have to answer these questions without students investigating themselves. This time I decided to use a method of inquiry used by Veritasium.
Derek Muller, the main host of the videos, usually goes to the streets and asks questions to ordinary people about a particular science concept. It is fascinating watching people try to verbalize and work through their thinking during the interviews. At the end Derek reveals "the answer" to the main question with easy to follow explanations. I wanted to incorporate that kind of inquiry into my class.
I decided to ask the question, "what makes a planet a planet?" to some of my fellow (non science) teachers. My plan was to ask a question that many people are familiar with, but have a hard time with the definition. I then wanted to show the video to my students so that they can see that this question is hard for learned adults as well as for students. Students then had to write their own definition of a planet and share with the class. I then gave them reading materials and showed a couple of videos that dealt with the concept. Then the students came up with their final answer and then had to share their results by speaking to the camera. The above video shows the teachers' responses and the students' responses to the teachers.
]]>Students in my classes have to determine if a substance has changed physically or chemically. In order to do that, they need to know if the properties of a substance has changed. We can look at many different properties of a substance such as color, density, boiling point, melting point, taste, texture, hardness, etc. One of the most exciting properties of matter is the color in which they burn. In the video above I show color flame candles and then show a demonstration of two different compounds, strontium chloride and copper sulfate, mixed with denatured alcohol, that produce large colorful flames.
]]>At the end of the year, students get a chance to be the scientists in several projects. One of my absolute favorites is the water bottle rocket. The video shows the general design of the rockets and several launches. What I love about the project is that they chose one variable to change that will increase flight distance. Variables include fin shape, fin size, fin placement, volume of water, etc. I also love that there is not just one design that works. Here is the handout that I give to students.
]]>Motion is the change in position over time. Students often have a difficult time understanding that concept graphically, which is one of the big 8th grade science standards. Vernier's Go!Motion sensor and software are excellent demonstration tools. The video demonstrates how both of them work together. Usually when I introduce it, I just give a volunteer student a big (1 x 1 yard) whiteboard and tell the student to walk towards and away from the sensor. The students can see the graph on the large video screen. They quickly pick up that the farther away from the sensor the student is, the higher on the graph the line is and vice versa. I have them draw graphs what what they think certain types of motion are and then we see if we can replicate the graph. The software also allows a prediction graph to be drawn and then students can see if they can walk that same motion graph. In later lessons, acceleration graphs are explored. Having a class set would be ideal, but having one sensor with a computer hooked up to a video projector will work just fine.
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