A recycling plant has chips of hight density poly(ethylene) (HDPE, d=0.92g.mL) used for plastic bottles and poly(vinylchloride) (PVC, d=1.406g/mL) used for plumbing and house siding. The chips of these two plastics were inadvertently mixed and it is your job to separate them. How would you do this?  

Expert Answers

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This is quite easy, with their different densities, particularly with the HDPE having a density less than one, and the PVC having a density greater than one. 

The density of water is 1 g/ml.  Materials with a density less than this will float, materials with a density greater than this will sink. 

.092g/ml<1g/ml, so the HDPE will float, if placed in a container of water.  1.406g/ml>1g/ml so the PVC will sink if placed in a container of water. 

To sort these two plastics, find a container that can hold water, and add enough water that you can separate the floating HDPE from the PVC that sank. 

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