OCR A Level CHEMISTRY PAPER 1 Questions and Answers

OCR A Level CHEMISTRY PAPER 1 Questions and Answers Test for carbonates - add dilute HCL - it makes carbon dioxide test for carbon dioxide by bubbling it through lime water Test for ammonium ions -add sodium hydroxide -warm the mixture -hover damp red litmus paper over it , if it turns blue the ions are present Test for sulphate ionz (SO4 2-) - add dilute HCL - then add BaCl2 - BaSO4 is made which is insoluble in water so a white precipitate will be formed Test for Halides (Cl-, Br-, I-) - add nitric acid - add silver nitrate - precipitates will be formed - Cl (white) , Br (cream) , I (yellow) Why add dilute acids when testing for ions ? it will get rid of any lurking anions that may create false positives Endothermic energy profile diagram products are higher than reactants Exothermic energy profile diagram reactants are higher than products What are standard conditions? 298K and 100kPa Enthalpy change of reaction the enthalpy change when the reaction occurs in molar quantities shown in the chemical equation under standard conditions Enthalpy change of formation the enthalpy change when 1 mole of compound is formed from it's elements in their standard states under standard conditions Enthalpy change of combustion the enthalpy change when 1 mole of a substance is burned completely in oxygen under standard conditions Enthalpy change of neutralisation the enthalpy change when an acid and alkali react under standard conditions to form 1 mole of water Bond dissociation enthalpy The enthalpy change required to break a covalent bond with all species in the gaseous state how to find out enthalpy change of combustion in the lab - burn the fuel - allow it to heat the water -work out the change in temperature of the water - use q=mct What happens to the rate of reaction when you increase temperature and why ? when you increase temperature rate of reaction increases - particles will have on average , more kinetic energy which means more particles will have at least activation energy and will undergo successful collisions What happens to the rate of reaction when you increase pressure when you increase pressure rate of reaction increases - particles will be closer together -they will collide more frequently -higher probability of successful collisions What happens to the rate of reaction when you use a catalyst and why ? rate of reaction will increase - catalysts provide an alternative reaction pathway witty a lower activation energy -therefore more particles will have at least activation energy (enough energy to react) Heterogenous catalyst -catalysts in a different PHASE(state) from the reactants -therefore the reaction happens over the surface of the heterogenous catalyst Homogenous Calalyst -catalysts in the same phase as the reactants - usually aqueous -the reactants combine with the catalyst to make an intermediate species who Ck reacts to form the products and reform the catalyst Why are catalysts used in industry? - Lower production costs - gives more product in a short time - help make better products (change the properties to make it more useful) - environmental sustainability How do catalysts contribute to environmental sustainability ? - lower temperatures and pressures needed so energy can be saved , less fossils fuels burned and less CO2 put in the atmosphere . fossil fuels reserved - reduce waste by allowing a different reaction to be used with a better atom economy Ways to investigate reaction rate - change in mass -volume of gas given off Le Chatelier's Principle if there's a change in concentration, pressure or temperature , the position of equilibrium will shift to counteract that change What effect do catalysts have on the position of equilibrium and why ? they have no effect as the speed up the rate of both reactions by the same amount . They cant increase yield but mean that equilibrium is reached faster What does a larger value of Kc mean? that the position of equilibrium is towards the right so there are more products in comparison to reactants Relative atomic mass the weighted mean mass of an atom of an element compared to 1/12 the mass of carbon-12 Relative isotopic mass The mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12.