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Offline xiankai

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question on acid and bases
« on: April 12, 2005, 07:38:57 AM »
im not really good at this stuff, but i have a few basic things i need to clear up:

1) what is hydrolysis? my faint idea is that its something to do with hydrogen...

2) whats the difference between H+ and OH- ionic bonding together to form water and the covalent bond of H2O

3) after KMnO4 is acidified into maganate ions floating with potassium ions and sulphate ions in the water, which ion is reduced to give the colourless solution after an reducing agent has been added?

4) in some colour tests, u add NaOH/aq NH3 to find out the cation. some hydroxides of the cation dont dissolve in NaOH/aq NH3 but some do. what is the theory behind this?

thanks.
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Offline AWK

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Re:question on acid and bases
« Reply #1 on: April 12, 2005, 09:08:17 AM »
AWK

tclam662

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Re:question on acid and bases
« Reply #2 on: April 17, 2005, 12:42:32 AM »
Nice to meet u :) I am not good either.... did touch any science for a long time. But i gonna take an University entryexam this July, so i have to pick up my book again ;(

1) Hydrolysis is a chemical process that molecule is broken down in to parts by the addition of water. For example the hydrolysis of ester

2) Water molecules are covalent compounds H-O-H, however it undergoes slight ionization to form a very small amount of hydrogen ions and hydroxide ions. but the degree of ionization is so small that the electrical conductivity of water is hard to be detected.( it is an explaination from my O-Level text book, i remember that there is a much bettee explaination in A-level, but i havent come to that yet)

3)MnO4-(purple) -> Mn2+(colourless), in acid/ alkaline medium, KMnO4 can perform its reducing property as H2O. H+/OH- are provided.

MnO4- + 3SO32- + 2H+ -> Mn2+ + 3SO42- + H2O

4) hm.... i dont know this reaction

Offline Donaldson Tan

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Re:question on acid and bases
« Reply #3 on: April 17, 2005, 02:29:33 AM »
KMnO4 can perform its reducing property as H2O. H+/OH- are provided.

Actually, I can't decipher what tclam662 mean by that clause. MnO4- is a strong oxidising agent in acidic medium, a weak oxidising agent in alkali medium. MnO4 reduces to Mn2+ in acidic medium but reduces to MnO2 in alkali medium.

4. If the precipitate dissolves, it normally involves formation of complex ions. Eg. addition of aq. NH3 causes Cu(OH)2 to precipitate. However, if u add excess NH3, Cu(NH3)42+ forms. It reduces [Cu2+] thus the Cu(OH)2 present in the mixture will dissolve to increase [Cu2+].
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

Offline xiankai

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Re:question on acid and bases
« Reply #4 on: April 19, 2005, 05:17:44 AM »
Actually, I can't decipher what tclam662 mean by that clause. MnO4- is a strong oxidising agent in acidic medium, a weak oxidising agent in alkali medium. MnO4 reduces to Mn2+ in acidic medium but reduces to MnO2 in alkali medium.

4. If the precipitate dissolves, it normally involves formation of complex ions. Eg. addition of aq. NH3 causes Cu(OH)2 to precipitate. However, if u add excess NH3, Cu(NH3)42+ forms. It reduces [Cu2+] thus the Cu(OH)2 present in the mixture will dissolve to increase [Cu2+].

thanks, i used to wonder where MnO2 fitted into the equation, but dismissed it as a case of wrong equation... until i saw your answer

and your last answer also enlightened me alot, thanks again!  :)
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