| Date | May 2011 | Marks available | 2 | Reference code | 11M.3.hl.TZ2.C3 |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Explain | Question number | C3 | Adapted from | N/A |
Question
Liquid-crystal displays are used in digital watches, calculators and laptops.
Kevlar is a condensation polymer that is often used in liquid-crystal displays. A section of the polymer is shown below.
Explain the strength of Kevlar in terms of its structure and bonding.
Explain why a bullet-proof vest made of Kevlar should be stored away from acids.
Markscheme
(Kevlar has) strong hydrogen bonds between chains;
creating a very ordered/strong structure;
acid donates a proton to the O and N atoms;
breaking the hydrogen bonds;
Examiners report
The concept of liquid-crystals was generally understood, but students often failed to obtain full marks because their answers were not detailed enough. In (b) they generally named some properties.
In (c), many candidates did not realize that Kevlar is lyotropic. They generally obtained at least one mark explaining the strength of Kevlar, but could not explain why it should be stored far away from acids.
The concept of liquid-crystals was generally understood, but students often failed to obtain full marks because their answers were not detailed enough. In (b) they generally named some properties.
In (c), many candidates did not realize that Kevlar is lyotropic. They generally obtained at least one mark explaining the strength of Kevlar, but could not explain why it should be stored far away from acids.
