Investigating Substances In The Sim Answer Key
Stetson Saenz
Note: This video is designed to help the teacher better understand the lesson and is NOT intended to be shown to students. It includes observations and conclusions that students are meant to make on their own.
Students will be able to identify and control variables to design an experiment to see whether the temperature of a solvent affects the speed at which a solute dissolves. Students will be able to explain, on the molecular level, why increasing temperature increases the rate of dissolving.
Remind students of the experiment they did in Lesson 4 in which they placed an M&M in water and watched the colored sugar coating dissolve. In that experiment, students used water and then alcohol and oil to see if the solvent used affects the dissolving of the M&M coating.
Students will record their observations and answer questions about the activity on the activity sheet. The Explain It with Atoms & Molecules and Take It Further sections of the activity sheet will either be completed as a class, in groups, or individually, depending on your instructions. Look at the teacher version of the activity sheet to find the questions and answers.
More color and sugar dissolve from the M&M in the hot water and less in the room temperature and cold water. This means there is more chocolate visible on the M&M in the hot water than there is in the room temperature and cold water. The color and sugar in the room temperature water dissolve somewhere between the cold and hot water but are more similar to the cold than the hot.
Note: There are actually two processes happening in this activity. The color and sugar are dissolving in the water, but they are also diffusing in the water. The temperature of the water affects the amount of dissolving, but it also affects the rate of diffusion. Students should focus on the surface of the M&M to judge the amount of color and sugar that dissolves.
Less sugar is visible in the hot water than in the cold, meaning that more sugar dissolves in the hot water than in the cold water. There is no obvious difference between the amount of salt that dissolves in the hot water compared to the cold water. This shows that temperature affects the dissolving of sugar more than it affects the dissolving of salt.
Help students understand that the graph shows that more sugar dissolves in water as the temperature of the water increases. Also help them to see that the dissolving of salt also increases as the temperature of the water increases. But the dissolving of salt does not increase nearly as much as sugar.
Note: Students may ask why so much more sugar dissolves at higher temperatures compared to salt. This is not easy to explain on the molecular level at a middle school, high school, or even college level. Tell students that since substances are composed of different atoms, ions, and molecules, they are held together differently and interact with water differently. Changing temperature also affects the motion of the atoms, ions, or molecules of the substance and affects the interaction between water molecules and the particles of the substance. There are so many factors involved that it is difficult to explain why the solubility of one substance is affected more than another by an increase in temperature.
Tell students that they will plot the solubility of potassium chloride on a graph provided on the activity sheet. Explain that potassium chloride is used as a salt substitute for people who should not eat regular salt (sodium chloride.)
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A substance is anything that takes up space and has mass. Substances can exist in solid, liquid, and gas form. When you mix two substances and you might or might not create something new, and it all depends on what two substances you are mixing. Ripping, tearing, smashing, stirring, squishing, and changing the shape of a substance by mixing it with another is called a physical change. Chemical changes occur when a new, third substance is created by combining two substances. Signs of a chemical change include, release of heat, bubbles, a color change, and smells!
Sarah has a big box where she keeps her toys. She has all kinds of toys: wooden horses, plastic legos, dolls, stuffed animals, and even metal race cars! When Sarah plays, she puts everything out on the carpet, and when she cleans up she puts them all back in her big box. When Sarah was cleaning up yesterday, she saw that one of her race cars was orange and rusty! Her grandma said it's because it got wet. Which of the answer choices is NOT true about Sarah and her big box of toys?
Sydnie is making a sand castle on the beach. She mixes water with her sand to make sure it's wet enough to mold into the shapes she wants. Is Sydnie making a new substance when she mixes sand and water? How do you know?
A mixture is when two or more substances are combined to create something new. The substances can remain separate like a salad or trail mix, but still, something new is formed. Another type of mixture is a solution when one substance dissolves into another like salt being stirred into water.
Many people have the misconception that once a substance has been mixed into a liquid that it cannot be separated. When something like salt is stirred into water, it seems to disappear, so the thought of separating it can be hard to imagine. There is no way to sift the salt out or remove the salt pieces with forceps. If the water is set in the sunlight, it will begin to evaporate and leave behind the salt that was mixed in.
All of the answer choices are examples of mixtures. Smoke is a mixture of ash and air, trail mix is a mixture of all of the different ingredients (raisins, peanuts, chocolate chips, etc.), and a closet of clothes is a mixture of varying clothing types (pants, dresses, skirts, shirts, hats, etc.). All of these answer choices have at least two substances that are mixed to form something new.
The students in the class created a new substance when they mixed the water and pepper, but the change is only physical. The pepper can be separated from the water, and there is no permanent change to either substance. There was no change in smell or color, and no new substance was formed as in a chemical change.
Separating a mixture is a way to reverse the creating of something new. If sand and rocks were mixed, a mixture was made with the two substances. It can be changed, and the mixture separated if the stones and sand are sifted. The small grains of sand will fall through the sifter leaving the rocks on top and separated.
A cancer cluster refers to the occurrence of a greater than expected number of cancer cases among a group of people in a defined geographic area over a specific time period. A cancer cluster may be suspected when people report that several family members, friends, neighbors, or coworkers have been diagnosed with the same or related types of cancer.
Some cancer clusters have been shown through careful investigation to be the result of a specific cancer-causing substance in the environment. However, such findings are extremely rare. One review of 576 cancer cluster investigations conducted over 20 years found that for only 72 of the apparent clusters could an increase in cancer rate be confirmed (1). Only three of the 72 clusters could be linked to a possible exposure, and in just one case was a clear cause identified.
Concerned individuals should contact their local or state health department to report a suspected cancer cluster or to find out if one is being investigated (2). Health departments provide the first response to questions about cancer clusters because they, together with state cancer registries, will have the most up-to-date data on cancer incidence in the area. The U.S. Centers for Disease Control and Prevention (CDC) website provides links to state and local health departments. These agencies may also be listed in the blue pages of government listings in telephone books.
Although potential cancer clusters are evaluated primarily by state and local health departments, states may request technical advice or assistance from several federal agencies: the CDC; the Agency for Toxic Substances and Disease Registry (ATSDR), which is part of CDC; and the Environmental Protection Agency.
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