20. Polymerisation
A section of Chemistry, 9701
Listing 10 of 116 questions
Lactic acid, CH3CH(OH)COOH, is the only monomer needed to form the polymer polylactic acid, PLA. Draw a short length of the PLA polymer chain, including a minimum of two monomer residues. The methyl groups may be written as –CH3 but all other bonds should be shown fully displayed. Label one repeat unit of polylactic acid on your diagram. Give the name of the type of polymerisation involved in the formation of PLA and the name of the functional group that forms between the monomers. type of polymerisation functional group Predict whether PLA is readily biodegradable. Explain your answer. The proton (1H) NMR spectrum of CH3CH(OH)COOH in CDCl 3 is shown in . The proton NMR chemical shift ranges are shown in Table 8.1. Lactic acid δ / ppm Table 8.1 environment of proton example chemical shift range δ / ppm alkane –CH3, –CH2–, >CH– 0.9–1.7 alkyl next to C=O CH3–C=O, –CH2–C=O, >CH–C=O 2.2–3.0 alkyl next to aromatic ring CH3–Ar, –CH2–Ar, >CH–Ar 2.3–3.0 alkyl next to electronegative atom CH3–O, –CH2–O, –CH2–Cl 3.2–4.0 attached to alkene =CHR 4.5–6.0 attached to aromatic ring H–Ar 6.0–9.0 aldehyde HCOR 9.3–10.5 alcohol ROH 0.5–6.0 phenol Ar–OH 4.5–7.0 carboxylic acid RCOOH 9.0–13.0 Use and Table 8.1 to complete Table 8.2. Table 8.2 proton environment chemical shift (δ) name of splitting pattern –COOH CH –OH –CH3 Name the substance responsible for the peak at δ = 0.0. Explain why CDCl 3 is a better solvent than CHCl 3 for use in proton NMR. An impure sample of CH3CH(OH)COOH contains pentan-3-one as the only contaminant. The mixture is analysed using gas/liquid chromatography. The pentan-3-one is found to have a longer retention time than the lactic acid. Explain what is meant by retention time. Suggest suitable substances, or types of substances, that could be used as the mobile and stationary phases. mobile phase stationary phase Describe how the percentage composition of the mixture can be determined from the gas / liquid chromatogram.
9701_w23_qp_42
THEORY
2023
Paper 4, Variant 2
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Name an example of a synthetic polyester and a synthetic polyamide. polyester polyamide Polyesters and polyamides are formed by condensation reactions. Name a molecule which is commonly eliminated in such reactions. The table shows the repeat units of a number of polymers. Place a tick () against the ones which are biodegradable. polymer repeat unit biodegradable A O O n CH3 B O O O O n C O CH3O n D N H O n O N H Draw the structures of two monomers used to form polymer B. A section of polypeptide was hydrolysed and the following amino acids identified. amino acid formula T CH3CH(NH2)CO2H U C6H5CH2CH(NH2)CO2H V H2N(CH2)4CH(NH2)CO2H Which of the amino acids T, U or V has the highest pH in aqueous solution? Explain why. amino acid State how many different dipeptides could be formed from a reaction mixture consisting of amino acids T and U. Polypeptides contain a high proportion of carbon and hydrogen in their structures, yet many are soluble in water. By referring to the structure of a polypeptide, explain why.
9701_m16_qp_42
THEORY
2016
Paper 4, Variant 2
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Questions Discovered
116