Passage
Two key ingredients found in many soaps are PEG 150 distearate and ethylhexyl glycerin. Both can be synthesized from glyceryl tristearate (Figure 1) .
Figure 1 Formation of PEG 150 distearate and ethylhexyl glycerin from glyceryl tristearateThe first step in this process requires the saponification of glyceryl tristearate. The resulting stearate molecules can then react with PEG 150 in an acid-catalyzed Fischer esterification to form PEG 150 distearate. The glycerol produced during saponification is used as a nucleophile to form ethylhexyl glycerin through a base-catalyzed S_N2 reaction with an ethylhexyl halide.Studies have shown that hand washing with soap can substantially reduce the number of germs present on hands and that washing hands before preparing food is particularly effective in reducing illness. Researchers examined the effect of washing for 20 seconds with different amounts of soap containing PEG 150 distearate and ethylhexyl glycerin and found an inverse correlation between the volume of soap used and the amount of bacteria recovered from the hands. The data are shown in Figure 2.
Figure 2 Bacteria recovered from hands after washing with varying amounts of soapThe researchers then investigated the effect of hand washing with different kinds of soap on the transfer of bacteria from hands to objects. Volunteers washed with a fixed volume of soap for 30 seconds, then handled sterilized plastic spheres for 30 seconds. Bacteria were then recovered from the spheres. The results are shown in Table 1.Table 1 Bacteria Recovered from Objects
Adapted from Fuls JL, Rodgers ND, Fischler GE, et al. Alternative hand contamination technique to compare the activities of antimicrobial and nonantimicrobial soaps under different test conditions. Appl Environ Microbiol. 2008.
-Counting the number of bacteria recovered from which of the following would NOT help researchers verify that soap reduces the number of bacteria transferred to objects?

Question

Passage
Two key ingredients found in many soaps are PEG 150 distearate and ethylhexyl glycerin. Both can be synthesized from glyceryl tristearate (Figure 1) .

Figure 1 Formation of PEG 150 distearate and ethylhexyl glycerin from glyceryl tristearateThe first step in this process requires the saponification of glyceryl tristearate. The resulting stearate molecules can then react with PEG 150 in an acid-catalyzed Fischer esterification to form PEG 150 distearate. The glycerol produced during saponification is used as a nucleophile to form ethylhexyl glycerin through a base-catalyzed S_N2 reaction with an ethylhexyl halide.Studies have shown that hand washing with soap can substantially reduce the number of germs present on hands and that washing hands before preparing food is particularly effective in reducing illness. Researchers examined the effect of washing for 20 seconds with different amounts of soap containing PEG 150 distearate and ethylhexyl glycerin and found an inverse correlation between the volume of soap used and the amount of bacteria recovered from the hands. The data are shown in Figure 2.

Figure 2 Bacteria recovered from hands after washing with varying amounts of soapThe researchers then investigated the effect of hand washing with different kinds of soap on the transfer of bacteria from hands to objects. Volunteers washed with a fixed volume of soap for 30 seconds, then handled sterilized plastic spheres for 30 seconds. Bacteria were then recovered from the spheres. The results are shown in Table 1.Table 1 Bacteria Recovered from Objects

Adapted from Fuls JL, Rodgers ND, Fischler GE, et al. Alternative hand contamination technique to compare the activities of antimicrobial and nonantimicrobial soaps under different test conditions. Appl Environ Microbiol. 2008.
-Counting the number of bacteria recovered from which of the following would NOT help researchers verify that soap reduces the number of bacteria transferred to objects?

Quizplus · Accepted Answer

11ecba2d_1267_7f80_a3bf_cd76d20bac8a_MD0008_00 Experimental results must be verified by the proper controls, including positive and negative controls. Positive controls demonstrate what the results of an experiment would look like when the independent variable has the maximum possible effect on the dependent variable. Negative controls show what the results would look like if the independent variable had no effect. In the experiment that measures transfer of bacteria from hands to objects, a positive control would show the results where no bacteria are transferred. Counting the bacteria recovered from untouched spheres would serve as a good positive control and also demonstrate that the spheres have been thoroughly sterilized (Choice C). A negative control would show the number of bacteria transferred if the soap used is completely ineffective. Washing hands with water only or not at all prior to handling spheres would serve as good negative controls, showing the effect of water without soap and no soap and water (Choices B and D). Recovering bacteria directly from unwashed hands instead of from spheres that were handled by unwashed hands would not demonstrate the number of bacteria transferred. Educational objective: Experimental controls, including positive and negative controls, are required to demonstrate the validity of a test result. Positive controls show what the maximum effect would look like, and negative controls show what no effect would look like. Both must relate to the dependent variable being measured without influence from the independent variable.

Passage Two Key Ingredients Found in Many Soaps Are PEG 150