Observing Osmosis Lab Background Information: Molecules are in constant motion, and tend to move from areas of higher concentrations to areas of lower concentrations. Diffusion is defined as the movement of molecules from an area of high concentration to an area of low concentration. The diffusion of water molecules through a selectively permeable membrane is known as OSMOSIS. Selectively permeable means that some molecules can move through the membrane while other molecules cannot. Movement through membranes is called transport. Diffusion and osmosis are passive forms of transport; this means that no energy is required to move molecules from high concentration areas to low concentration areas. Active transport does require energy to move molecules from low concentration areas to high concentration areas. Osmosis is the movement (transport) of water through a selectively permeable membrane from an area of high concentration to an area of low concentration. Gummy Bears are popular candies made of gelatin, starch, and sugar. Page 1 of 5
Question: How will soaking Gummy Bear candies in different concentrations of salt water affect the size of the candy? Prediction (explain your prediction based on the background information): Materials: 2 Cups Marker Balance Metric Ruler Paper Towel Calculator Distilled Water 2 Gummy Bears Table Salt Procedure: 1. Using a marker, label each of your two cups with your names and the contents (concentrations) of the solutions in the cups. 2. Use the ruler to find the height and width of your two Gummy Bears. 3. Use a balance to find the mass of your two Gummy Bears. 4. Record descriptive observations about your Gummy Bears (color, texture, etc ) 5. Fill one of the cups with 150 ml of distilled water. 6. Fill the other cup with 150 ml of 10%, 20%, 40%, 60%, 70%, or 80% of salt water (teacher will assign which concentration you will be using). 7. Place one Gummy Bear in each cup. 8. Set the cups aside for 24 hours. 9. After 24 hours, gently take the bears out of the water and pat them dry. Be very careful because the candy is now extremely breakable. 10. Repeat steps 2-4. Group Data: Gummy Bear #1 Before soaking in distilled water After soaking in distilled water Gummy Bear #2 Before soaking in % salt water After soaking in % salt water Page 2 of 5
Calculate the percent change in the size of the candy: Distilled Water % CHANGE IN HEIGHT = (after soaking height before soaking height / before soaking height) X 100 % CHANGE IN WIDTH = (after soaking width before soaking width / before soaking width) X 100 % CHANGE IN MASS = (after soaking mass before soaking mass / before soaking mass) X 100 % Salt Water % CHANGE IN HEIGHT = (after soaking height before soaking height / before soaking height) X 100 % CHANGE IN WIDTH = (after soaking width before soaking width / before soaking width) X 100 % CHANGE IN MASS = (after soaking mass before soaking mass / before soaking mass) X 100 Page 3 of 5
Class Data - % Change Group # / Distilled Salt H 2 0 % Salt Group 1 10% Group 2 20% Group 3 40% Group 4 60% Group 5 70% Group 6 80% Average Graph the percentage change in mass of the class average (distilled water) versus the different concentrations of salt water in a bar graph. Hint you should have 7 bars total. (use create-a-graph to construct and print your graph attach it to this lab) Questions: 1. What happened to the candy after soaking in distilled water overnight? 2. Were you surprised with any of the % changes you observed (distilled water or any of the different salt water concentrations)? Explain any yes answers. 3. After this lab and the information you should have gained explain what happens to roadside plants during the winter, when the road gets salted to help with icy conditions. Page 4 of 5
Conclusion: Write a paragraph to explain the percent changes of size with the different concentrations of salt water solutions versus the distilled water. Use the concepts of osmosis in your explanation. Include specific data from this lab to support your conclusion. Page 5 of 5