AQA A-level CHEMISTRY 7405/1 Paper 1 CORRECT QUESTION AND ANSWER

AQA A-level CHEMISTRY 7405/1 Paper 1 CORRECT QUESTION AND ANSWER TOF steps - 1) ionisation 2) acceleration 3) ion drift 4) detection 5) analysis Electron impact - Sample vaporised and electron gun fires high energy electrons at it which knock off 1 electron from each particle, making them 1+ ions NB- can knock off more than one e or break molecular ion electrospray ionization - Sample dissolved in volatile solvent then injected through needle to give fine mist which is attached to positive end of high voltage power supply, particles gain proton NB- Mr of substance is actually one less than shown due to extra H+ Acceleration (TOF) - positive ions accelerated using electric field so they all have the same kinetic energy Ion drift (TOF) - particles with small mass have larger velocity do ions start to separate with lightest ions reaching detector first Detection (TOF) - positive ions hit negatively charged plate and gain an electron which forms a current, the larger the current the higher the abundance Analysis (TOF) - -computer uses data to produce mass spectrum which shows mass m / charge z ratio -mr or ar is furthest right peak (small peaks larger than mr are due to isotopes) -may be large peaks at lower mr due to fragmentation Electron spin - Property of electron (CW or ACW) Represented by up and down arrows Orbitals - Defined regions of space around nucleus where electrons most likely to be found, each orbital holds 2 electrons Hund's Rule - Electrons prefer to occupy orbitals on their own and only pair up when no empty or bait ask of same energy are available Electron configuration - 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 4d10 exceptions to electron configuration - chromium and copper, only take one electron in 4s orbital Why does ionization energy decrease down a group? - Atoms get bigger so electrons further away from nucleus, greater shielding Why does ionization energy increase across a period? - Atoms get smaller, nuclear charge increases, similar shielding Dip in ionisation energy groups 2-3 - Electrons take up higher orbital (s to p) which makes ionisation energy lower as higher orbitals have higher energy Dip in ionisation energy groups 5-6 - Electron- electron repulsion in orbital makes electron easier to lose Relative atomic mass - The average mass of an atom of an element/ 1/12th of the mass of an atom of carbon-12 Empirical formula - The simplest whole number ratio of atoms of each element present in a compound Percentage yield - actual yield/theoretical yield x 100 Atom economy - (Molecular mass of desired products/ Molecular mass of all products) x 100 Electronegativity - The power of an atom to attract electron density in a covalent bond towards itself electronegativity trend - increases across a period, decreases down a group Enthalpy change - Heat energy change measured at constant pressure Hess's Law - The Enthalpy Change for a chemical reaction is independent of the route taken Mean bond enthalpy - Energy required to break one mole of covalent bonds between two given atoms, averaged across a range of compounds Activation energy - the minimum energy colliding particles must have in order to react dynamic equilibrium - Forward and backward reactions take place at same rate so concentrations of products and reactants remain constant Only reached in closed system Le Chatelier's Principle - When a system at equilibrium is disturbed, the equilibrium shifts in the direction that reduces the disturbance Haber process conditions - - 200 atm : high pressures favour forwards reaction but are costly - 450°C : low temperature favours towards reaction but rate of reaction too slow at low temps - iron catalyst Effect of concentration on Kc - no effect Solubility of group 2 hydroxides - Solubility increases down the group Solubility if group 2 sulphates - Solubility decreases down group Use of Mg - Extract titanium from its ore TiCl4 + 2Mg - Ti + 2MgCl2 Use of Mg(OH)2 - Medicine as cure for indigestion Use of Ca(OH)2 - To neutralise acidic soils Use of CaO and CaCO3 - Flue gas desulphurisation Use of BaSO4 - Used as a tracer for x-rays Important that it is insoluble as it is safe to ingest Halogen bond energy - Energy if halogen- halogen bond decreases down group due to larger atomic nuclei NB fluorine is an exception as radii so small that there is repulsion between lone pairs Cl- with H2SO4 - Produces NaHSO4 and HCl Not redox as in change in oxidation state because Cl- not strong enough reducing agent Test for HCl with ammonia solution, white cloud produced Br- with H2SO4 - Produces SO2 S goes from +6 to +4 Test for SO2 if potassium dichromate goes from orange to green I- with H2SO4 - Produces H2S S goes from +6 to -2 Test for H2S with lead ethanoate which goes from white to black Bronsted-Lowry acid - proton donor