Displacement reactions. (1 Viewer)

[undalay]

Displacement reactions involve the loss and gain of electrons.

I would assume that the less electronegative elements would give there electrons to the more electronegative elements.
However the activity series given in CSU HSC online and the conquering chemistry lists Lithium as more reactive than Barium. However barium is actually more electropositive than lithium. http://en.wikipedia.org/wiki/Electronegativity

1. What else is there to consider beside electronegativity to determine which element will lose electrons and which will gain it ?

2. In the conquering chemistry book, there is this question:

By referring to the activity series 2.3, select three metals which will displace:
a) Lead from a solution of lead nitrate.

The answer is : Any three of Mg, Al, Zn, Fe (Ca, Ba, Li would react with water much more rapidly than with Pb)

Those this mean Ca, Ba, and Li are incorrect answers?
If so does this mean that Ca, Ba, Li cannot displace any metals since it reacts so vigorously with water? What other metals participate in a displacement reaction because of this reaction with water?

3. Will two different metals always displace eachother? I.e. If two metals are similar in activity will no reaction take place?

 

[Undermyskin]

3. No, it's either unobservable or non-existent. I think it happens for the groups of metals in brackets like those in Conquering chemistry.

2 and 1. If Ca, Ba, Li are wrong answers, I think the final products including at least one precipitate is counted and the rigorousness of reactions are taken into account...

 

[undalay]

Eh could you write in full sentences or something? i'm having a bit of trouble understanding what you are saying sorry >__>.

 

[nandayo]

1. I'd say the most obvious answer here is standard reduction potentials. The metal that is higher up on the reduction potentials table will displace the other corresponding metal.

2. I'd say so. K Na Ba Li Ca would all react immediately with water and disallow a reaction I spose. So Mg, Al, Zn, Fe would be the only correct answers...although I believe Manganese could be there too

3. No. For example when you calculate the EMF for the cell, and it ends up negative..it will not produce a current and therefore nothing is being oxidised or reduced, and therefore nothing is being displaced. So no, two different metals will not always displace each other.

 

[WantToDoBetter]

Lol, streching my memory here....
1. Standard reduction potentials are definatly the way to go for a serious chemist but if u want to try a short cut Fluorine is the most electronegative element and everything that moves away from it is less and less electronegative. An elements ionisation energy also needs to be considered. Ionisation energy is the amount of energy needed to remove an electron from orbit (it increase with electron at the electron pull closer to the neuclus). Eg. Group 1 elements have very low ionsation energies.

2.Unsure, but probabley has something to do with the presence of the electronegative elements in tap water F and Cl, but again just speculating...

3. This is an easy one. Just check your reactivity series. If the element that is in the dissovled salt form is BELOW the metal you are using to displace it, a reaction will occur. The closer the metals in the reactivity series the slower the reaction, the further apart, the more 'funner'. Example zinc chloride (ZnCl) (trasition metal variable valence, please excuse) is in solution and your drop some aluminium foil in (Al). The Zinc will be displace on to the surface of the aluminium foil and the aluminium will go into solution as aluminium chloride (AlCl3). AGAIN THE METAL IN SOLUTION !!!MUST!!! BE !!!LOWER!!! ON THE REACTIVITY SERIES FOR A REACTION TO OCCUR. If it's not then no reaction will take place.
Cheers .

 

[Undermyskin]

I'm so sorry for the mess-up before.

ok.
3. Reactions always occur tho at times very slowly. The exact experimental answer can only be achieved in ideal condition with pure chemicals. What I said about the 'group' is that Conquering Chem place metals in order of decreasing reactivity:

{K,Na} then {Ca, Ba} {Mg, Al, Zn, Fe} and so on. So, the reactions between elements in the same {} will be much harder to occur. It does NOT mean the reaction don't occur.

(sorry for the answer before 'cuz i was thinking about galvanic cells.)

To nandayo: What do you mean tho? To be more accurate, you should gather info about their reduction potentials up to 3 d.p. if you are using Volt meter as a tool to determine, that's not accurate as its resistance will prevent any current less than 0.02V

1. I can't think of anything else.

2. The info of this question is not sufficient, I think. With very concentrated PbNO3, the amount of water available after its reaction with Ca is not high. So if you and more Ca, this Ca with reaction with PbNO3 simultaneously. Ca(OH)2 is only sparingly soluble so you can even get Pb(OH)2 to be accurate. The final products include: Pb(OH)2 (little), Ca(OH)2 (depends on how much water is available) as precipitate. Ca(NO3)2 and Pb(NO3)2. This is messy as I go more deeply, eh? Just don't want to miss any possibility.

PS: Mg is never included with Na, K, Li, Ba and Ca! it can only react with steam!!!

 

[nandayo]

To nandayo: What do you mean tho? To be more accurate, you should gather info about their reduction potentials up to 3 d.p. if you are using Volt meter as a tool to determine, that's not accurate as its resistance will prevent any current less than 0.02V

Was talking about electrolytic reactions, but I suppose the anode and cathode will 'swap roles' anyway if no current is provided. So strictly speaking I should have said yes but it's a notable exception...even if they still do displace each other, it's not spontaneously.

 

[WantToDoBetter]

Was talking about electrolytic reactions, but I suppose the anode and cathode will 'swap roles' anyway if no current is provided. So strictly speaking I should have said yes but it's a notable exception...even if they still do displace each other, it's not spontaneously.

I think your a tad mixed up. If you are refering to electrolytic reactions, then you are refering to electrolysis which is of course the spilting of a molten substance (electrolyte) by passing an electric current though it and by doing so attacting the respected ions to the cathode (attracts cations) and anode (attracts anions)which are of course, inert. This cannot be measured though the use of the standard reduction potiential and therefore has no relevance on displacment reactions for another two reasons:
1. Electricity is USED in this process, not CREATED though the oxidation and reduction though two metals of different reaction potentials.
2. The cathode and anode isn't being ionically linked (but it is being oxidised and reduced, hence the charge).

BUT, the good news is we know that you were talking about a galvanic or voltaic cell, just thourgh i'd clear up the terminology .
It is also my understanding that you cannot get a negative FINAL number when calulating the EMF of a galvanic cell. It's been a few months so please correct me if i'm wrong.
Cheers!