OCR A-Level Chemistry – Organic Chemistry. Exam Questions with Complete Solutions

What are biodegradable plastics? - Ans .-Broken down by enzymes What are photodegradable plastics? - Ans .-Broken down by U.V. Light What is the general formula of alkanes? - Ans .CnH2n+2 Are alkanes saturated or unsaturated and why? - Ans .-Saturated -Each carbon atom forms four strong covalent, single, sigma bonds around it Are alkanes polar or non-polar and why and how does this affect their solubility and reactivity? - Ans .The electronegativities of carbon and hydrogen are very similar so the C-H sigma (σ) bonds are nonpolar As a result of this, alkanes are nonpolar molecules and have no partial positive or negative charges (δ+ and δ- respectively)Alkanes therefore do not react with polar reagentsThey have no electron-deficient areas to attract nucleophilesAnd also lack electron-rich areas to attract electrophiles What is the melting and boiling points of alkanes like? - Ans .-as chain length increases so does the strength of the intermolecular forces as there is greater surface area for contact between molecules and hence stronger london forces and therefore the melting/boiling points are highr for longer chain. What is a structura/chain isomer? - Ans .-Same molecular formula but a different structural formula What are the rules with structural isomers? - Ans .-Affect carbon chain length -Alkyl side chain cannot be on the first carbon - the overall carbon chain length must remain the same -Cyclic alkanes are not structural isomers of alkanes (they a are structural isomers of alkenes) What are cycloalkanes? - Ans .alkanes in which the carbon atoms are arranged in a ring, or cyclic, structure general formula CnH2n What is the combustion of an alkane? - Ans .-The reaction of the alkane with O2 -Exothermic When does complete combustion take place? - Ans .-When there is excess oxygen available What are the products of complete combustion? - Ans .-CO2 and H2O How do you balance alkane combustion equations? - Ans .1. C 2. H 3. O How does the energy required/released in complete combustion change with increasing carbon chain length? - Ans .-More energy is released to from the products -More energy is required (to break the bonds in the reactants - activation energy), therefore it is harder to burn When does incomplete comubstion take place? - Ans .-When there is a limited supply of oxygen What are the products of incomplete combustion? - Ans .-CO and H2O What is the problem with carbon monoxide? - Ans .-It is highly toxic -It binds irreversibally to the haemglobin in your red blood cells forming carboxyhaemglobin -Less O2 is transported around the body When is incomplete combustion more