Leaving certificate chemistry
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| What is Oxidation? | Oxidation is the addition of oxygen to a substance / gain of electrons
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| Define Oxidation Number! | Oxidation number is the charge that an atom has or appears to have when electrons are distributed according to certain rules.
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| What are the rules for assigning oxidation numbers?s | 1. ox. no uncombined element is 0
2. of ion =charge
3. in compund sum of ox. no. =0
4. oxygen= -2 except with peroxides
5. hydrogen =1
6. halogens=-1
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| When does oxygen not have an ox. no. of -2? | In peroxides, then it has oxydation number -1. And in OF2 when it has a oxidation number of +2
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| When does hydrogen have an oxydation number of -1? | In metal hydrides. eg. NaH (H=-1)
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| What oxydation numbers have halogens? | They have an oxidation number of -1 unless bonded with more electronegative atom. eg. Cl2O where Cl=1
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| What happens to the oxidation number when an element is oxidised? | oxidation is an increase in oxidation number.
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| What happens when if chlorine water and potassium bromide solution are poured into a test tube? | Colourless potassium bromide turns yellow (orange) due to formation of Br2
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| Write the equation for the reaction between potassium bromide and chlorine water! | Cl2 + 2Br- -> 2Cl- +Br2
0 -1 -1 0
Cl is the oxidising agent
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| What happens when chlorine water is added to potassium iodide? | colourless potassium iodide turns reddish brown. due to the formation of I2.
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| Give the half equations of the oxidation/ reduction reaction of potassium iodide and chlorine water! | Oxidation: 2l- ---> I2 + 2e-
Reduction: Cl2 + 2e- ---> 2Cl-
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| What happens when bromine water is added to potassium iodide solution? | turns into a reddish brown colour due to the formation od I2.
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| Give the half equation of the oxidation reduction reaction of potassium iodide and bromine water! | Oxidation: 2l- ----> I2 +2e-
Reduction: Br2 + 2e- ----> 2Br-
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| What happens if chlorine water is added to a sodium sulfite solution? what happens when barium chloride is added? | no change is observed. when barium chloride is added aa white precipitate is formed.
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| Some HCL is added to a chlorine water/ sodium sulfite solution with some barium chloride, what is observed? | If the white precipitate does not dissolve in dilute HCL, then sulfate ion is present. ie. the chlorine has oxidised the sulfite io (+4) to the sulfate ion (+6)
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| Give the hlf equations of the reaction of chlorine with sodium sulfite! | Oxisdation: SO3-- + O ----> SO4--
Reduction: Cl2 +2e- -----> 2Cl-
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| What happens if chlorine water is added to iron(ii) sulfate solution? | no apparent change is observed.
when dilute hydroxide solution is added a greenish brown precipitate is formed.
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ValerieKripp
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