Basic acid/base questions (1 Viewer)

[Shoom]

Hi

Acids are substances capable of providing hydrogen ions for chemical reactions, free hydrogen ions are available in solutions only ( is this because only when a substance is in a solution it seperates into ions?)

My book then says free hydrogen ions are available only i solutions where the minute proton is stabilised bby association with a solvent molecule in aqueous solutions it exists as the hydronium ion.

I dont get that last paragraph can someone explain it to me, is ti saying that the hydrogen ions provided by acids in solutions are only in the form of hydronium?

 

[danz90]

In aqueous acid solutions, where water is obviously present, H3O+ ions are formed, NOT H+, because the following reaction occurs:

eg. HCl + H2O --> Cl- + H3O+

HCl donates a H+ proton to H2O, as per definition of Bronsted-Lowry acids.

Whenever an acid ionises, think of it as donating a H+ to the base (in the above example, H2O is theoretically acting as a base, since it accepts a proton from the acid, HCl.)

Don't get confused by weird sentences in textbooks.. it should be a simple thing.

 

[minijumbuk]

It's just that H+ ions can never exist on their own. They have too little electronegativity, so they almost instantaneously sticks to a H2O particle to form a coordinate covalent bond, forming H3O+.

 

[Shoom]

Thanks, very clear explanation

 

[Shoom]

Ok, another question.

A galvanic cell consists of two half cells. A particular example, one half cell has a zinc electrode in zinc nitrate solution, the other half cell has a copper electrode placed in copper nitrate solution.

It says thgat zinc atoms lose electrons at the zinc electrode and eneter the solution as as zinc ions.

How are zinc ions formed in the solution why are they formed. If this helps the salt bridge is KNO3. It then goes onto say that the electrons lost from the zinc atom go to the othe half cell to the copper electrode, here copper ions gain electrons and deposit as copper metal????
I dont get how the Zinc and Copper ions are formed, and why the copper ions gain the two loose electrons to form copper metal.

Ok, do the zinc ions formed travel through the salt bridge or do they just hang around in the zinc half cell?

The part im stucj at is understanding how the ions are formed in each half cell.

 

[danz90]

Ok, another question.

A galvanic cell consists of two half cells. A particular example, one half cell has a zinc electrode in zinc nitrate solution, the other half cell has a copper electrode placed in copper nitrate solution.

It says thgat zinc atoms lose electrons at the zinc electrode and eneter the solution as as zinc ions.

How are zinc ions formed in the solution why are they formed. If this helps the salt bridge is KNO3. It then goes onto say that the electrons lost from the zinc atom go to the othe half cell to the copper electrode, here copper ions gain electrons and deposit as copper metal????
I dont get how the Zinc and Copper ions are formed, and why the copper ions gain the two loose electrons to form copper metal.

In galvanic cells... the oxidant and reductant are separated so that direct displacement doesnt occur and thus an electric current can be produced.
If you placed a piece of zinc metal in a copper sulfate solution, then the zinc would displace Cu2+ ions in solution.. forming Zinc ions and Cu metal solid. This is because oxidation and reduction occurs, which release energy... usually in the form of heat if the oxidant and reductant are in the same container or in contact - but in a galvanic cell, they are separated, and the energy is released as a flow of electrons (ill go into this a bit later)

Zinc readily oxidises to form Zn2+ ions: Zn(s) --> Zn2+ + 2e-

The electrons released then travel across a wire into the cathode half-cell... where they are 'consumed' by the copper cathode (which is copper solid), where Cu2+ ions from the copper solution are reduced to copper solid:

Cu2+ + 2e- --> Cu(s)

Note that the electrons for the reduction of copper are provided by the oxidation of Zinc (anode).

In order for an electric current to be produced... the salt bridge containing KNO3 is in place to allow K+ to migrate towards the cathode.. and anions (which have a negative charge - just as electrons do) and NO3- to the anode. Therefore... electrical neutrality is promoted.. and a flow of electrons is established - hence producing electrical current.

You have to remember: In the activity series, a metal will displace the ions of another metal below it in the activity series, for reduction.

My explanation is a bit shonky, i've never liked galvanic cells etc .. hope it was a help though.

 

[Shoom]

Thanks for your help!.

An Anion is a negatively charged ion, so the ion gains electrons. So why is the zinc half cell made up of a zinc anode when it gives up electrons? yet the copper half cell is the cathode but the copper accepts electrons?

thats what im stuck at.

Or am I confised because im thinking of this in terms of ions should I think of it in terms of redox reactions which if thats the case the zinc half cell will be the anode because it has a mostly negative charge because it loses electrons which have a negative charge and then the copper is reduced so it sorta becomes positive?

if thats the case why do the positive potassium ions go towards the cathode and negative NO3 ions towards the negative half cell?

Sorry I must sound really stupid, but this is confusing me.

 

[Shoom]

Ok, I should just remeber this wherever oxidation occurs is the anode cell, wherver reduction takes place is the cathode cell.

Will the anode always be on the left?

so then why are positive ions ( potassium entering the anode)?

 

[brenton1987]

so then why are positive ions ( potassium entering the anode)?

The anode is oxidised so the anode becomes negatively charged. The cathode becomes positively charged, and cations in solution are reduced onto the cathode as metal.

Now the anode solution is positively charged and the cathode solution is negatively charged. Nitrate anions from the salt bridge will diffuse into the anode cell while potassium and zinc cations will diffuse into the cathode.

Make sense? I can draw and post some pictures if you want.