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Leaving certificate chemistry

What is Oxidation? Oxidation is the addition of oxygen to a substance / gain of electrons
Define Oxidation Number! Oxidation number is the charge that an atom has or appears to have when electrons are distributed according to certain rules.
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
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
When does hydrogen have an oxydation number of -1? In metal hydrides. eg. NaH (H=-1)
What oxydation numbers have halogens? They have an oxidation number of -1 unless bonded with more electronegative atom. eg. Cl2O where Cl=1
What happens to the oxidation number when an element is oxidised? oxidation is an increase in oxidation number.
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
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
What happens when chlorine water is added to potassium iodide? colourless potassium iodide turns reddish brown. due to the formation of I2.
Give the half equations of the oxidation/ reduction reaction of potassium iodide and chlorine water! Oxidation: 2l- ---> I2 + 2e- Reduction: Cl2 + 2e- ---> 2Cl-
What happens when bromine water is added to potassium iodide solution? turns into a reddish brown colour due to the formation od I2.
Give the half equation of the oxidation reduction reaction of potassium iodide and bromine water! Oxidation: 2l- ----> I2 +2e- Reduction: Br2 + 2e- ----> 2Br-
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.
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)
Give the hlf equations of the reaction of chlorine with sodium sulfite! Oxisdation: SO3-- + O ----> SO4-- Reduction: Cl2 +2e- -----> 2Cl-
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.
Created by: ValerieKripp