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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: clıppy on October 13, 2012, 10:26:01 pm

Title: Quick Acid and Base Questions
Post by: clıppy on October 13, 2012, 10:26:01 pm

Hi guys I just have a few acid and bases questions I'm hoping i could get answered:

• For the ionization of perchloric acid in water: HClO₄ + H₂O --> H₃O⁺ + ClO₄^-
  Which of the following species would have the lowest concentration? - HClO₄, H₂O, H₃O⁺, ClO₄^-
  
• In a 0.001 M solution of the weak acid C₂H₅COOH the pH will be closest to? - 2, 3, 4, 9
• Are there always Hydronium and Hydroxide ions in an acid and base even before it reacts with something else?
• What is the difference between a dissociation, ionization and hydrolysis reactions?

I've got a test and sac coming next week for them both so if anyone has some good tips or info about those, I'd appreciate it too.
Thanks

Title: Re: Quick Acid and Base Questions
Post by: Tonychet2 on October 13, 2012, 11:19:20 pm

clo4- for the first one because there is extra h3o+ from the self ionisation of water
and since its a weak acid it is only partially ioniased so the reactants are out of the equation

Title: Re: Quick Acid and Base Questions
Post by: Tonychet2 on October 13, 2012, 11:20:40 pm

question 2 is 4 i think, because 0.001M of a weak acid u can assume about 10% of it will be ionised so the H+ conc is 0.0001M, that gives u pH of 4

Title: Re: Quick Acid and Base Questions
Post by: Nobby on October 13, 2012, 11:25:10 pm

Nah the first will be HClO₄; perchloric acid is stronger than sulfuric acid.
Second should be closest to pH 4.
Third, yes, it ionizes to H₃O⁺ and the conjugate base (or OH^- and conjugate acid).
Fourth, I'm not too sure, but I'd say dissociation is when an ionic species is split into smaller ones, ionization when a species is ionized (not necessarily dissociation, look up Mass Spectrometry), and hydrolysis when a species reacts with water and has a condensation reaction-formed bond split.

Title: Re: Quick Acid and Base Questions
Post by: sin0001 on October 13, 2012, 11:28:35 pm

For the last question, I would say disassociation & ionization are basically the same things (i.e. a molecule breaking apart into ions). Hydrolysis is also similiar to these terms, it's a reaction in which water is a reactant, pretty much means dissolving.

Title: Re: Quick Acid and Base Questions
Post by: Nobby on October 14, 2012, 01:11:25 am

Quote from: sin0001 on October 13, 2012, 11:28:35 pm

For the last question, I would say disassociation & ionization are basically the same things (i.e. a molecule breaking apart into ions). Hydrolysis is also similiar to these terms, it's a reaction in which water is a reactant, pretty much means dissolving.

This is all wrong.

The reaction N₂O₄ --> 2NO₂ is dissociation, but not ionization.
CH₄ + e^- --> CH₄⁺ + 2e^- is ionization but not dissociation.
HCOOCH_3(aq) + H₂O --> HCOOH_aq + CH₃OH_(aq) is hydrolysis, but neither dissociation, ionization nor dissolution.

Title: Re: Quick Acid and Base Questions
Post by: kenhung123 on October 14, 2012, 02:00:43 am

Dissociation and ionisation are classical terms that confuse people. Dissociation is when a substamce breaks down into 2 or more simpler substances.

Ionisation is the process which forms ions. Note that in an *ionic* compound such as NaCl(s), as it breaks down into Na+ and Cl-, we are not forming ions, these ions are already present in the lattice. The ions are simply separated from the lattice into free ions that are hydrated by water molecules. So that is why this process is called dissociation as opposed to ionisation.

Title: Re: Quick Acid and Base Questions
Post by: sin0001 on October 14, 2012, 11:02:49 am

Woops, I guess I was confused with these terms too then