# Diffusion and Osmosis Objectives: 1. To observe the diffusion of a food

Diffusion and Osmosis
Objectives:
1. To observe the diffusion of a food dye in a dish of water.
2. To measure the effect of temperature on the rate of diffusion.
3. To observe the effect of different concentrations of solutions on the process of osmosis.
Materials:
thermometer
ruler
Petri dishes
Skittles or food coloring or M& M’s
Gummy bears
Tea cup or glass
Method:
1. First, look at the data table below to review the type of data that will be collected.
2. Trace the Petri dish on a piece of paper. Next, draw a line to bisect the circle. Mark the line to the
nearest 0.5 cm. (Ex, 0, 0.5, 1.0, 1.5, 2.0, 2.5, etc.)
3. Fill a glass with tap water and ice. After 15 minutes record the temperature. Place one edge of the Petri dish on the zero mark that was drawn on the piece of paper. Fill the Petri dish with the ice water. Place one Skittle or one drop of food coloring into the dish at the zero mark.
4. Record the distance that the dye travels every minute, to the nearest 0.5 cm. Record data for ten minutes.
5. Repeat the procedure using the warmest water from the faucet. Use the same color skittle or food coloring.
Record the water temperature and the data obtained.
Interpreting the Data (How to Determine the Rate of Reaction)
1. You use that data to create a set (X,Y) to insert into the point slope formula.
2. Graph the data that was collected. The data for room temperature water is provided below. You need to determine the average values for the room temperature data since two trials were conducted.
3. Take a look at the data table. To determine the rate for the cold temperature reaction I determined X by choosing two times 5 minutes and 10 minutes. Then, to determine Y look at the distance traveled, 1.5 and 3 cm respectively. (Shown in yellow below.) You can choose any points, I just chose the ones used randomly.
4. These are the data points that you will substitute into the formula: (1.5, 5) and (10, 3).
5. Now, plug into the point slope formula: Slope = m = Y1 – Y2
X1 – X2
6. That’s it! Now discuss the differences any in the graph and the slopes obtained. Give reasons why any differences may have occurred.
DATA: (Shown in yellow.)
Rate of Diffusion (cm) Temp. = 21 oC Room Temp.
21 oC ~____ oC ~____ oC
Average Cold Hot
Time ( min) Trial I (cm) Trial II (cm) (Total / 2) (cm) (cm) (cm)
0 0 0 0 0 0
__1___ __ 1___ ___1__ _____ ___ ___
__2___ ___2__ ___1__ _____ ____ ___
__3___ ___2__ ___1__ _____ ____ ____
__4__ ___3__ ___2_ _____ ____ ____
__5___ __ 3___ ___2_ _2.5__ ____ ____
__6___ ___4__ ___3_ _____ ____ ____
__7___ ___4__ ___3__ _____ ____ ___
__8__ ___5__ ___4_ _____ ____ ____
__9__ ___5__ ___4_ _____ ____ ___
__10___ ___6__ ___5__ _____ ____ ____
1. Complete the data table by calculating the average rate of diffusion for the data collected (in blue).
2. Construct a graph for the information collected for the average rate of diffusion for all three temperatures.
3. Place the three graphs on the same paper and construct a key for each graph.
4. Determine the slope of each graph using the point slope formula:
Slope = m = Y1 – Y2
X1 – X2
Questions:
Describe what was observed in the video of the Elodea and explain what is meant by Brownian motion?
2. What magnification was used in Slide # 9, a view of Elodea using 10 X ocular & 100 X objective lens?
3. Why is diffusion considered to be passive?
4. What do the following terms mean? Draw a picture of one Elodea cell immersed in the following solutions (Diffusion powerpoint Slide #27). Include arrows and labels (High Concentration. Equal Concentration, Low concentration) to show the direction that water is flowing. (Use drawings similar to the ones viewed in the power point.)
a. Isotonic
b. Hypertonic
c. Hypotonic
5. a. Determine the rate of diffusion (the slope) for the three temperatures tested.
b. Which temperature demonstrated the lowest rate of diffusion?
c. Which showed the highest rate of diffusion (the largest slope)?
d. Explain why there might be a difference.
6. Determining the effect of osmosis.
Method:
Obtain 2 gummy bears of equal size. Place each one on a piece of paper and trace them. Remove the gummy bear, then measure the height and width of the tracing to the nearest mm. Record the data in a data table. Fill one cup with 50 ml of tap water. Fill the second dish with 50 ml of tap water and add two teaspoons of salt; stir the mixture. Place a gummy bear into each dish and allow them to remain in the solution for two hours. Stir the cup every 30 minutes by gently swirling the cup.
After two hours, remove each gummy bear, gently pat dry, then trace it. Measure the height and width of the tracing to the nearest mm.
Data Interpretation: Compare the sizes of the gummy bears before and after being placed in the solution and record any difference.
a. What is osmosis?
b. Draw a picture of a gummy bear and explain the results that were observed. Include arrows and labels (High Concentration. Equal Concentration, Low concentration) to show the direction that water is flowing. (Use drawings similar to the ones viewed in the power point.)