AQA A LEVEL Chemistry Questions and Answers

AQA A LEVEL Chemistry Questions and Answers Relative atomic mass The average mass of an atom of an element, relative to 1/12th of the mass of an atom of Carbon-12 Relative molecular mass Average mass of a molecule compared to 1/12th of the mass of a carbon-12 atom The Avogradro constant the number of particles in a mole ideal gas equation pV = nRT empirical formula the simplest whole number ratio of atoms of each element in a compound percentage atom economy (Mass of desired product/total mass of reactants) x 100 ionic bonding the electrostatic attraction between oppositely charged ions in a lattice covalent bond a shared pair of electrons between non-metal elements co-ordinate bond a shared pair of electrons where both electrons are supplied by one atom repulsion in shapes of molecules Lone pair-lone pair > lone pair-bonding pair > bonding pair-bonding pair electronegativity the power of an atom to attract the pair of electrons in a covalent bond hess' law Total enthalpy change for a reaction is independent of the route chosen mean bond enthalpy The energy required to break a covalent bond into gaseous atoms averaged over different molecules Bonds broken - bonds made activation energy The minimum amount of energy needed to start a chemical reaction catalyst A substance that increases the rate of a chemical reaction without being changed by providing an alternative reaction pathway by lowering activation energy Le Chatelier's principle When a system in dynamic equilibrium is subjected to change, the position of equilibrium will shift to oppose the change. oxidising agents electron acceptors reducing agents electron donors Enthalpy of formation Enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions in their standard states Enthalpy of atomization The energy required to produce one mole of gaseous atoms from an element in its standard state Electron affinity the enthaply change when one mole of gaseous atoms forms one mole of -1 ions Lattice enthalpy of formation Enthalpy change when one mole of a solid ionic compound is formed from its constituent ions in the gas phase Lattice enthalpy of dissociation Energy change when 1 mol of an ionic lattice dissociates to its gaseous ions. standard electrode potential 298K 100kPa 1.00moldm-3 Electrode reactions in lithium cell (positive electrode) Li+ + CoO2 + e- → Li+[CoO2]- Electrode reactions in lithium cell (negative electrode) Li → Li+ + e- Electrode reactions in hydrogen-oxygen fuel cell in acidic conditions (positive electrode) 02 + 4H+ +4e- -> 2H20 Electrode reactions in hydrogen-oxygen fuel cell in acidic conditions (negative electrode) H2 -> 2H+ + 2e- Brosted- lowry Acid proton donor Brosted- lowry base proton acceptor weak acids partially dissociate in aqueous solution what is an acidic buffer made of? weak acid and its salt what is an basic buffer made of? weak base and its salt spontaneous reactions when enthalpy is negative and entropy is positive ( spontaneous at all temperatures) when enthalpy is positive and entropy is negative (not spontaneous at any temp) Stereoisomerism Molecules with the same structural and molecular formula but have a different spatial arrangement Enthalpy change Heat energy change at constant pressure Oxidation of primary alcohols Aldehyde (Alcohol in excess + product distilled off immediately) Carboxylic acid (oxidising agent in excess + Under reflux ) Oxidation of secondary alcohols Ketones No further oxidation Oxidation of tertiary alcohols Can't be easily oxidised as they do not have two hydrogen atoms directly attached to he carbon that is bonded to the OH group but can be oxidised by hot nitric acid Oxidising agent for oxidation of alcohols Acidified potassium dichromate Orange (Cr2O7 2-) to green(Cr 3+) What happens when an unsymmetrical alcohol undergoes and elimination reaction A mixture of isomeric products are produced Biofuel Any fuel made from living organisms or their waste Carbon neutral No net annual emissions of carbon dioxide into the atmosphere Line with largest m/z ratio on a mass spectrum of a compound Molecular ion (a molecule which had lost an electron) High resolution spectrometry Used to distinguish between compounds and can measure relative atomic masses to 4 decimal places Finger print region The area of the spectrum below the 1500cm-1, it is unique to the molecule Molecular formula The actual number of stones of each element imma compound Functional group isomer Compounds with the same molecular formula but different functional group Positional isomer Isomers with the same carbon chain and the same functional group but attached at different points of the carbon chain Specific heat capacity Energy required to raise the temperature of 1g of a substance by 1 degrees Solvents used for nmr CCL4, CDCL3 Do not cause peak on h nmr but causes known peak on carbon nmr Carboxylic acid + carbonates Salt, carbon dioxide + water Carboxylic acid + alcohol Ester + water Uses for esters Food colouring, perfumes, solvents and plasticisers Uses for sulfur dioxide Bleach, food preservatives Acid hydrolysis of esters Acid and alcohol Base hydrolysis of esters Carboxylate ion and alcohol Hydrolysis of oils and fats using NaOH Glycerol, soap (salt if long chain carboxylic acid) How are biodiesel made Reacting vegetable oils with methanol and KOH Makes glycerol and methyl esters Uses for quaternary ammonium salts Fabric cleaners, hair products enthalpy of hydration Enthalpy change when 1 mole of gaseous ions becomes aqueous ions intial rate of reaction The rate of reaction at time t = 0 s. Used to compare the effect on the rate of changing the independent variable. rate determining step The slowest step in a reaction mechanism equivalence point The point during a titration when the number of H+ ions and OH- ions are equal. This is at the middle of the steepest part of the titration curve. buffer A solution that resists changes in pH when small amounts of acid or base are added. autocatalyst Catalyst that is a reaction product transition metal elements that form colored ions in solution and have multiple oxidation states ligand an ion or molecule with at least one lone pair of electrons that can form a coordinate bond to a metal atom or ion complex a central metal ion or atom surrounded by ligands co-ordination number Number of lone pairs bonded to the metal ion hemoglobin protein structure containing four haem groups bonded to four flobular proteins - used for gas exhange chiral carbon A carbon atom attached to four different atoms or groups of atoms. hetregenous catalyst A catalyst that is in a different phase from that of the reactant substances. homogenous catalyst A catalyst that is in the same phase as all the reactants and products in a reaction system enantiomers Non-superimposable mirror image race mate/ racemic mixture 50/50 mixture of left and right enantiomers immiscible liquids that are not soluble in each other condensation polymers polymers formed from when monomers join together and eliminate a small molecule such as water or hydrogen chloride addition polymers polymers madenfrom alkenes in an addition reaction zwitterion dipolar ion formed when amino acids undergo an internal acid-base reaction mobile phase from chromatography, the liquid or gas used to move the sample up the stationary phase stationary phase The phase that does not move in chromatography perfect ionic model Ions which are perfect spheres with no covalent character isotopes atoms with the same number of protons but different number of neutrons Alkali a soluble base First ionisation energy the enthaply change when one mole of electrons is remoeved fromone mole of gaseous atoms to form one moles of gaseous ions with a single positive charge Dative covalent bond When an electron pair donated by one molecule is shared between two molecules Activation energy the minimum amount of energy required to start a chemical reaction Disproportionation when a substance is oxidised and reduced in a reaction to produce two different products Anion A negatively charged ion Cation A positively charged ion atom economy molecular mass of the desired product/ sum of the molecular masses of all reactants x100 Dynamic Equilibrium a equilibrium where both the forward and reerse reactions are occuring a the same rate and the concentrations of the reactants and products remain constant