Questions on Pracs (1 Viewer)

[raidmaster212]

just a cuple of questions please ... i have 2 practicals to do: one on combustion of alcohols and one fr galvanic cells just got sum questions


Combustion of Alcohols:

Q1:Which of these fuels would be considered the fuel of the future and why : ethanol methanol propanol
Q2: Which fuel has the highest molar heat of combustion : methnol ethanol and propanol ( i know its propanol but y)


Galvanic Cells:

Q1: explain why volume of electrolyte in half cell affects current and not voltage
Q2: It is necessary to measure curent output of the cell quickly because this tends to decrease steadily with time. outline why this occurs
Q3: the operation of a cell might considered to depend on the electron attraction of zinc and copper ions. which ion is a stronger competitor for electrons?


please answr the ones u can.. thanx in advance

 

[munchiecrunchie]

combustion of alcohols

Q1 : ethanol
Q2 : propanol - has highest molar mass and hence upon heating will release the most energy

 

[raidmaster212]

please is there anyone else that can answer my questions

 

[xiao1985]

Q1) ethanol, since it may be obtained, and used in a renewable manner

Q2) propanol. experimental data tells us so. If you really want to know why, you can look up the concept of heat of formation. In short, for every bond broken, you require energy. For every bonds formed, you release energy. Combustion of propanol forms alot more H-O and C=O bonds than methanol or ethanol. Although the energy required to bread the bonds are greater, too, still more net energy would be released.


edit

Galv Cell
Q1) I feel dubious about this statement. Firstly, volume of electrolyte clearly will not influence the voltage, since voltage is an inherent property of a galvanic cell, with defined anode and cathode, and electrolyte being 1M. 2ndly, Current is the measure of number of electrons passing through a particular point per unit time. If anything, I would think the S.A. of electrode with electrolyte would influence the current, not the volume itself.

Q2) I'll assume you've learnt Le Chatelier's principle.
Let's take Cu2+ | Cu || Zn | Zn2+ as an e.g.

Cathode: Cu2+ + 2 e- <---> Cu(s)
Anode: Zn <---> Zn2+ + 2e-

The standard potential you see on the potential table is set assuming electrolytes (i.e. Cu2+ and Zn2+) are at concentration of 1M. But as you can imagine, the more the experiment progresses, the more Zn2+ would be produced, and the more Cu2+ will be consumed. Resulting in the distrubance in equilibrium. Therefore, the voltage will diminish as the galv cell works on.

Q3) in short: Zn has lower electronegativity, so it exerts less pull on electrons. what you will see is that electrons will flow from Zn to Cu.

 

[raidmaster212]

lol thanx for the info xiao ... but it was a little too late .. i had to hand in my assignment on tuesday... so i just answered the questions as best as i could ... and yes i do know le chatliers principle'