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| Pregunta | Respuesta |
| List the oxidation number rules | 1) An uncombined element = 0 2) Uncombined ions = their charge 3) Sum of ox numbers in a molecule = its overall charge 4) F is always -1 5) H is always +1 except in metal hydrides 6) O is always -2 except in peroxide and w/ F 7) Cl is -1 except w/ O or F |
| Define: standard electrode potential | The voltage measured under standard conditions when the half cell is connected to a standard H electrode |
| The stronger the reducing agent the more ______ its electrode potential | +ve |
| The stronger the oxidising agent the more ______ its electrode potential | -ve |
| A +ve emf means the fwds reaction is... | SPONTANEOUS |
| Standard conditions for measuring emf | All solutions 1mol/dm3 1ATM pressure 25\(\omicron\)C or 298K Connection made using an inert platinum electrode |
| Describe a standard H electrode | Hydrogen gas being bubbled into a 1M solution of \(H^+\) at 1ATM pressure around a platinum electrode. |
| Oxidation occurs at the anode of cathode? | Anode |
| Is a drawn cell diagram has electrons flowing clockwise is this the same as LHS/RHS on cell diagram notation? | Yes |
| What is a salt bridge? | Filter paper soaked in \(KNO_3\) to balance out the charges in the 2 beakers/solutions |
| In cell diagrams, where is the oxidised from positioned? And is that the one w/ or w/o \(e^-\)'s separate? | Next to the salt bridge W/ electrons |
| Above what voltage does emf have to be for a reaction to go to completion? | +0.6V |
| Electrode potential is directly proportional to what 2 things? | Total entropy and the equilibrium constant |
| Why are predictions about reaction feasibility based on electrode potentials not always correct? | Electrode potentials are to do with energetic stability not kinetic so a reaction can be spontaneous but extremely slow because of a high activation energy Also it may not be occurring at standard conditions. |
| What are the colours of each of the V oxidation states? | \(VO_2^+\) +5 yellow \(VO^{2+}\) +4 blue \(V^{3+}\) +3 green \(V^{2+}\) +2 mauve |
| Why when oxing V from +5 to +4 can the solution turn green even though there is no \(V^{3+}\)? | Because as some of the yellow \(VO_2^+\) turns blue the colours mix together before it all becomes blue \(VO^{2+}\) |
| What colour is \(MnO_4^-\) and what is Mn's ox state? | Purple +7 |
| What colour is \(Mn^{2+}\)? | colourless |
| In which reaction does auto catalysis occur? | Manganate (VII) with ethandioic acid |
| What is the formula of ethandioc acid? | \(C_2O_4^{2-}\) |
| What colour and state is CuI? | White solid |
| When estimating % Cu in an alloy what can cause uncertainties? | \(I_2\) can evaporate \(CuI_{(s)}\) ppt can mask the end point You are assuming that the solutions are all evenly mixed. |
| \(H_2\) + air is explosive but it is safer than petrol or aviation fuel. Why? | It has a low density |
| What type of electrode is used in a H fuel cell? | A gas permeable platinum one with a catalyst |
| What is in a H fuel cell? | Proton exchange membrane Electrolyte Electrodes \(O_2\) and \(H_2\) pumped in |
| Product of an H fuel cell | water |
| Problems with a H fuel cell | \(H_2\) is mostly produced from electrolysis of water or natural gas requiring electricity from power stations using fossil fuels. |
| List 3 ways methanol can be sourced | Fossil fuels Agricultural biomass waste Chemical recycling of \(CO_2\) |
| Waste products of a methanol fuel cell | \(CO_2\) and water |
| 2 advantages and a disadvantage of methanol over hydrogen | Easier to store because it doesn't need high pressures or low temperatures. The amount of energy contained in a given volume is much greater than even highly compressed hydrogen. Efficiency is low because alcohol can pass through the present available membranes. |
| How is ethanol produced? | By fermentation of sugar cane |
| Which is more toxic methanol or ethanol? | Methanol |
| A's and D's of fuel cells | Far less pollution than a normal car At least twice as energy efficient at converting fuel to power as a power station. It is expensive to make and use toxic chemicals that need to be disposed of. They have a limited life span. |
| How does a FC breath analyser work? | A microprocessor measures the current produced by the cell when alcohol in a person's breath is oxidised to a carboxylic acid. |
| Problems with breath analysers | They must be calibrated regularly and they only give the composition of the air breathed out. |
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