Key 1.16 JDL

# Key 1.16 JDL - Note that we are assuming that the iron...

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Key for Micro Exam 1 Question 16 JDL edit Question 16: The mass of an alloy (a simple mixture) of aluminum and iron is 20 kg. The densities of iron and aluminum are 8 g/cm 3 and 4 g/cm 3 respectively. What is mass of the aluminum if the iron atoms occupy 2000 cm 3 of the total volume of the alloy? Answers: (a) 8 x 10 3 g (b) 4 x 10 3 g (c) 16 kg (d)12 kg (e) 10 kg (f) Impossible to solve We want to find the mass of the aluminum in the alloy. To do so, we must first subtract the mass of iron out of the total 20 kg mass. Since the density of iron is 8 g/cm 3 and we know it occupies 2000 cm 3 of the alloy, we can calculate its mass through dimensional analysis as shown below.
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Unformatted text preview: Note that we are assuming that the iron atoms occupy the same total volume when mixed with the aluminum atoms as they would if they were alone. This may or may not be true, but as is often the case in science, we here have to make a simplifying assumption—indeed, we can’t do the problem without making this assumption. 2000 cm 3 | 8 g iron | 1 kg = 16 kg iron | 1 cm 3 | 1000 g Now we need to subtract this mass from the total mass to find the aluminum mass. 20 kg – 16 kg = 4 kg Since this is not one of the answer choices, we should try converting it to g. 4 kg | 1000 g = 4000 g = 4 x 10 3 g | 1 kg...
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