OCR A A Level CHEMISTRY | Questions and Answers with complete solution

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 100kPaEnthalpy 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 collisionsWhat 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