Passage II
Seven 4 g mixtures of glycerol and agar were prepared, each having a different percent glycerol by mass. A plastic film was made from each mixture; all the films were rectangular and had the same dimensions.
Each film was clamped and stretched (see Figure 1) at 25°C until it broke.
Three properties of the film were determined:
• Tensile stress, the force applied per unit area of the film as the film broke
• Percent elongation, given by:
• Elastic modulus, a measure of the rigidity of the film
The results for all 7 films are shown in Figures 2 and 3.
Figures adapted from Eugene S. Stevens et al., "Polymer-Plastics Experiments for the Chemistry Curriculum." @2006by Division of Chemical Education, lnc., American Chemical Society.
7. A student predicted that as the percent glycerol by mass increased from 20% to 45%, the elastic modulus would decrease by more than 2,000 MPa. Do the results shown in Figure 3 support this claim?
Your Answer is
Correct Answer is C
Explanation
It can be seen from figure 3 that when percent glycerol by mass=20, elastic modulus=2500 MPa; when percent glycerol by mass=45, elastic modulus=300 MPa. So the prediction in the question stem is correct