The diagram shows a section of the material chosen to insulate a signal cable at a tidal-energy station. The cable may be splashed with a sodium chloride so...
Question 1 Report
The diagram shows a section of the material chosen to insulate a signal cable at a tidal-energy station. The cable may be splashed with a sodium chloride solution, so the coating must not allow water to reach the metal. Fig. 1 represents one repeat unit of the polymer. The bonds continuing beyond the brackets show that many units are joined together.
Fig. 1
(a) Name the monomer used to make this polymer. [1]
(b) Draw the displayed formula of this monomer. [2]
(c) State the type of reaction that changes the monomer into the polymer. [1]
(d) Explain why this polymer coating helps to prevent corrosion of the metal conductor when the cable is in contact with salt water. [3]
Answer Details
(a) The monomer is chloroethene. The polymer repeat unit has the arrangement \(\mathrm{-CH_2-CHCl-}\), so the monomer must have had a double bond between these carbon atoms. [1]
(b) The displayed formula of chloroethene is:
This shows \(\mathrm{CH_2=CHCl}\) with all bonds. [2]
(c) The reaction is addition polymerisation. [1]
(d) The polymer forms a continuous barrier around the metal conductor. This prevents water reaching the metal and also prevents sodium chloride solution, including its ions, reaching it. Without water and salt solution at the conductor, the conditions required for corrosion are removed. [3]
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