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40 Cards in this Set
- Front
- Back
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What is the oxidation number of an element? |
The measure of the number of electrons an atom uses to bond with atoms of another element. |
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What is the sum of the oxidation numbers of a neutral compound? |
0 |
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What is the sum of all the oxidation numbers in an ion equal to? |
The charge of the ion |
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What is the oxidation number of a uncombined element, e.g. Br2? |
0 |
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In which compounds is the oxidation number of oxygen not -2 and what is it? |
In peroxides e.g. H2O2 it is -1. |
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What is the oxidation number of hydrogen in compounds usually? |
+1 |
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In which compounds is the oxidation number of hydrogen -1? |
hydrides |
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What is the oxidation number of group 3 elements? |
+3 |
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What is the oxidation number of group 7 elements? |
It can have different oxidation numbers assume it is -1 unless you are askedto find it. |
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What is a redox reaction? |
A reaction where both oxidation and reduction take place. |
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What is a disproportionation reaction? |
One where the same element is both oxidised and reduced. |
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What is a redox reaction? |
A reaction where both reduction and oxidation occur. |
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What is a reducing agent? |
A reagent that reduces (adds electrons to) anothr species. |
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What is an oxidising agent? |
A reagent that oxidises (takes electrons from) another species. |
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True or false electrons are included in the overall equation? |
false, they are only included in the half equation. |
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What is the total increase in osidation number equal to? |
total decrease in oxidation number. |
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What is the first step in constructing a redox equation from oxidation number? |
identify the reactants and products from information given. |
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what is the second step in constructing a redox equation from oxidation numbers? |
Balance only the elements which are being oxidised or reduced and identify tehir total change in oxidation number. |
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What is the 3rd step of constructing a redox equation from oxidation numbers? |
balance the change in oxidation number total incresease=total decrease. |
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What is the last step in constructing a redox equation from oxidation numbers? |
check if any other element needs balancing to give a redox equation |
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What kind of agent is acidified manganate (VII)? |
strong oxidising agent. |
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What is the formula for acidified potassium manganate? |
KMNO4 |
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What is the colour of manganate ions? MnO4- |
purple |
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What are MnO4- ions reduced to in a redox titration? |
Mn2+ ions |
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What colour are Mn2+ ions? |
Very pale pink (almost colourless) |
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When using acidified manganate (VII) in a redox titration which ions are in the burette? |
purple manganate (VII) ions (oxidising agent) |
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What is the reducing agent when doing a redox tirtration with acidified manganate? |
usually Fe2+ |
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When is the redox reaction using acidified potassium manganate complete? |
When a permanent pale pink colour is acheived. |
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What colour is Fe2+(aq)? |
pale green |
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What is the ratio Fe2+:MnO4- |
5:1 |
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What is colour change atcomplete oxidation (of Fe2+ ions)? |
The solution in the conical flask turns from pale green to permanent pale pink |
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What is the colour of aqueous iodine? |
brown |
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What is the redox reaction between Fe2+ and MnO4-? |
5Fe2+ +MnO4- + 8H+ ------> Mn2+ +5Fe3+ +H2O |
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What is the redox reaction between thiosulfate and iodine? |
2S2O32- +I2 ----> 2I- +S4O62- |
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What is the name of S2O32-? |
Thiosulfate ion |
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What is S2O32- oxidised to? |
S4O62- |
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What is thiosulfate ion oxidised to? |
tetrathionate ion |
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What is the problem when just using aqueous iodine as an indicator for the end point of redox reaction? |
When iodine is reduced to iodide the brown colour fades gardually and it is diffucult when all the brown as disappeared. |
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What indicator is added to see the exact point when all the I2 has been reduced? Describe the colour change |
starch indicator is added. The solution turns blue-balck in presence of iodine. As thiosulfate is added teh solution starts to turn grey to pale yellow. The endpoint is when all the blue-black has disappeared. |
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Why is the I2/S2O32- redox titration useful? |
It is useful in the analysis of: copper (I) compound household bleach (ClO-) A copper alloy. |
