Fig. 1 shows labels printed by scanners at a recycling plant. The plant separates a solid food-wrapper plastic from rigid window-frame offcuts before either...
Question 1 Report
Fig. 1 shows labels printed by scanners at a recycling plant. The plant separates a solid food-wrapper plastic from rigid window-frame offcuts before either material is melted. A student also heats a small sample of the window-frame plastic in a tube. The gas is passed into water to make an acidic solution. The apparatus is supported by an iron clamp. The recycling manager records the mass of poly(ethene) collected during one day.
The mass of poly(ethene) sent into the recycling process is 250 kg. The plant recovers 84% of this mass as clean plastic pellets.
(a) Name the polymers identified by scanners P and Q. [2]
(b) Give the formula of the monomer used to make each polymer in Fig. 1. [2]
(c) Explain why the two plastics should be sorted before they are melted and made into new products. [3]
(d) State the colour change when moist blue litmus paper is placed in the acidic gas produced from scanner Q material. [2]
(e) Calculate the mass of clean poly(ethene) pellets recovered. Show your working. Calculate the mass not recovered, and state one reason why this mass is lower than the mass of plastic put into the process. [4]
Answer Details
(a) Scanner P identifies poly(ethene). Scanner Q identifies poly(chloroethene), also called PVC. [2]
(b) The monomers are:
For poly(ethene): \(\mathrm{C_2H_4}\) or \(\mathrm{CH_2{=}CH_2}\).
For poly(chloroethene): \(\mathrm{C_2H_3Cl}\) or \(\mathrm{CH_2{=}CHCl}\). [2]
(c) The plastics have different chemical compositions: poly(chloroethene) contains chlorine, whereas poly(ethene) does not. Mixing them could give a recycled material with unsuitable or unpredictable properties. Also, heating poly(chloroethene) can form acidic, corrosive hydrogen chloride. [3]
(d) Moist blue litmus paper turns red, because the gas dissolves in water to form an acidic solution. [2]
(e)
\[\text{mass recovered}=250\times\frac{84}{100}=210\text{ kg}\]
\[\text{mass not recovered}=250-210=40\text{ kg}\]
The plant recovers 210 kg of clean poly(ethene) pellets and does not recover 40 kg. The missing mass may be lost during sorting or washing, remain contaminated, or be rejected because it is not poly(ethene). [4]
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