Key 1.4 JDL (1)

# Key 1.4 JDL (1) - Key for Micro Exam 1 Question 4 JDL edit...

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Key for Micro Exam 1 Question 4 JDL edit Question 4: (Do this type of problem on paper without a calculator. Take it step by step using dimensional analysis. Make appropriate approximations where necessary to choose the logical answer from the choices below.) How many neutrons are found in a 5.0 pmol sample of 90 Zr? Answers: A) 1.5 x 10 14 B) 1.5 x 10 17 C) 1.5 x 10 20 D) 3.4 x 10 20 E) 3.0 x 10 16 F) 3.409 x 10 17 G) none of these Dimensional analysis is a method for converting units. This requires a process of step-by-step conversions to reach an overall conversion. Here, the question essentially asks you to convert pmol of 90 Zr to numbers of neutrons. A model for the conversion is illustrated below. Notice how the units are consistently aligned diagonal to each other so that they cancel each other out until the final conversion to neutrons is reached. 5.0 pmol 90 Zr | 1 mol 90 Zr | 6 x 10 23 atoms 90 Zr | 50 neutrons | 10 12 pmol 90 Zr | 1 mol 90 Zr | 1 atom 90 Zr To set this up, first convert pmol to mol. Remember that there are 10 12 pmol in 1 mol. Next use

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