Flashcards
Unit 5 Redox flashcards
Cards in this deck (35)
- 1List the oxidation number rules1) 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 - 2Define: standard electrode potentialThe voltage measured under standard conditions when the half cell is connected to a standard H electrode
- 3The stronger the reducing agent the more ______ its electrode potential+ve
- 4The stronger the oxidising agent the more ______ its electrode potential-ve
- 5A +ve emf means the fwds reaction is...SPONTANEOUS
- 6Standard conditions for measuring emfAll solutions 1mol/dm3
1ATM pressure
25\(\omicron\)C or 298K
Connection made using an inert platinum electrode - 7Describe a standard H electrodeHydrogen gas being bubbled into a 1M solution of \(H^+\) at 1ATM pressure around a platinum electrode.
- 8Oxidation occurs at the anode of cathode?Anode
- 9Is a drawn cell diagram has electrons flowing clockwise is this the same as LHS/RHS on cell diagram notation?Yes
- 10What is a salt bridge?Filter paper soaked in \(KNO_3\) to balance out the charges in the 2 beakers/solutions
- 11In 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 - 12Above what voltage does emf have to be for a reaction to go to completion?+0.6V
- 13Electrode potential is directly proportional to what 2 things?Total entropy and the equilibrium constant
- 14Why 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. - 15What 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 - 16Why 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 \(VO^{2+}\)
- 17What colour is \(MnO_4^-\) and what is Mn's ox state?Purple
+7 - 18What colour is \(Mn^{2+}\)?colourless
- 19In which reaction does auto catalysis occur?Manganate (VII) with ethandioic acid
- 20What is the formula of ethandioc acid?\(C_2O_4^{2-}\)
- 21What colour and state is CuI?White solid
- 22When 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. - 23\(H_2\) + air is explosive but it is safer than petrol or aviation fuel. Why?It has a low density
- 24What type of electrode is used in a H fuel cell?A gas permeable platinum one with a catalyst
- 25What is in a H fuel cell?Proton exchange membrane
Electrolyte
Electrodes
\(O_2\) and \(H_2\) pumped in - 26Product of an H fuel cellwater
- 27Problems 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.
- 28List 3 ways methanol can be sourcedFossil fuels
Agricultural biomass waste
Chemical recycling of \(CO_2\) - 29Waste products of a methanol fuel cell\(CO_2\) and water
- 302 advantages and a disadvantage of methanol over hydrogenEasier 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. - 31How is ethanol produced?By fermentation of sugar cane
- 32Which is more toxic methanol or ethanol?Methanol
- 33A's and D's of fuel cellsFar 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. - 34How 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.
- 35Problems with breath analysersThey must be calibrated regularly and they only give the composition of the air breathed out.
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- A2 level Chemistry (Unit 5) Flashcards on Unit 5 Redox flashcards, created by J000D97 on 04/04/2015.
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- J000D97 · Apr 2015
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- Nov 25, 2016
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