Chemistry and Physics some Keypoints/Notepoints (onDemandOnly) !! :)

[knowitall10]

anyone knows how to calculate the percentage uncertainty? is there a formula or somethin ?

You mean percentage error?

 

[knowitall10]

iKhaled follow this link (Without google, i would die)
http://chemistry.about.com/od/chemistryquickreview/a/experror.htm

 

[xhizors]

anyone knows how to calculate the percentage uncertainty? is there a formula or somethin ?

(Uncertainityx100)/Original Value = %uncertainity
for relative uncertainity you dont multiply it by 100

 

[iKhaled]

iKhaled follow this link (Without google, i would die)
http://chemistry.about.com/od/chemistryquickreview/a/experror.htm

we would all die without internet

 

[knowitall10]

(Uncertainityx100)/Original Value = %uncertainity
for relative uncertainity you dont multiply it by 100

What's the difference between relative uncertainty and uncertainty?

 

[knowitall10]

Guys/Gals: 2 Questions:
1) Up there in the post, i mentioned that the book states graphite electrodes..does that mean inert electrodes in general or precisely graphite?
2) What's the difference between relative uncertainty and uncertainty?
Jazakum Allahu Khair for replying.

 

[1357913579]

Guys/Gals: 2 Questions:
1) Up there in the post, i mentioned that the book states graphite electrodes..does that mean inert electrodes in general or precisely graphite?
2) What's the difference between relative uncertainty and uncertainty?
Jazakum Allahu Khair for replying.

2)relative error is fractional error

 

[knowitall10]

2)relative error is fractional error

Jazak Allahu Khair.
Can you please be a bit elaborate? aren't they all in the end of the day, fractional?

 

[1357913579]

Jazak Allahu Khair.
Can you please be a bit elaborate? aren't they all in the end of the day, fractional?

different names they are because i my self didn't know what it was just saw on your link it was written it equal to eror over oroginal value meaning it the fractional error btw this name is never mentioned in paast papers or Cie books so u shouldn't woory much about it

 

[1357913579]

and regarding graphite i didnt really got what u want to ask because we use graphite because its inert and obviously we use it in its pure form because impurities will effect its properties

 

[knowitall10]

and regarding graphite i didnt really got what u want to ask because we use graphite because its inert and obviously we use it in its pure form because impurities will effect its properties

Jazak Allahu Khair Brother.
What I'm saying is that my book states "when using graphite electrodes". so when electrolysing aq solutions, do we only use graphite electrodes, or any other inert electrode like platinum?

 

[1357913579]

• Assalamu Alaykum Soldier313 and @everyone who had this doubt (long ago)

Remember when you had asked that question on P4 as to why when electrolysing some aq comp'ds you get one product that doesn't match the answer of the marking scheme? (I'm really sorry brother xhizors i do not mean to discuss any pp's here-this is a conceptual explanation).

Yeah...well, to you and to anyone who didn't know this:
the electrolysis of aq solutions depends on:

• the relative electrode potential of the ions
• the conc of the ions

Considering Electrode Potentials:

The more positive the electrode potential of the cation, the greater the ease of discharge at the cathode. (Look the uploaded photo)
At the anode, using graphite electrodes*, the ease of discharge of the anions follows the order: ( look at uploaded photo)
If the conditions are standard, the conc. of aq. solutions is 1.00mol/dm3 with respect to the ionic comp'd dissolved in water. but the conc of hydrogen and hydroxide ions in solution is very low. as long as the difference in electrode potential values is greater than 0.30V, the predictions are highly likely to occur.
Considering Solution Concentration:
When aq. solutions are electrolysed, the ions are rarely present at conc of 1.00 mol/dm3. For eg. when aq NaCl is electrolysed, chloride ions are discharged at the anode in preference to the hyrdoxide ions. now after looking at that uploaded photo, you'll be like WHAT!!!!! but calm down
This is because chloride ions are present at a much higher concentration than hydroxide ions. The chloride ions fall below the hydroxide ions in the discharge series.
But what happens when we electrolyse an extremely dilute solution?
Again, we find that O2, rather than Cl2 is discharged off at the anode for similar reasons as described above.
Guys/Gals, one thing to note is that The proportion of oxygen increases the more dilute the solution.
*Now my question: I don't understand why the book says graphite electrodes specifically...does it mean inert electrodes?

exactly regarding the "Solution Concentration" this is basically what u studied in olevels and As even in A2 but its mostly asked in AS not in paper-4 because in paper-4 (A2) this want u to use the electrode potential to solve the problem having said that they stil have discussed about the concentration thingy in the Cie book A2 portion its exactly as written here just to add a point maybe its even written here it that
at cathode: which are low in reactivity series (less capability of forming ions more power to be reduced or better oxidising agents) those are discharged at cathode
for anode: which have more concentration

 

[knowitall10]

exactly regarding the "Solution Concentration" this is basically what u studied in olevels and As even in A2 but its mostly asked in AS not in paper-4 because in paper-4 (A2) this want u to use the electrode potential to solve the problem having said that they stil have discussed about the concentration thingy in the Cie book A2 portion its exactly as written here just to add a point maybe its even written here it that
at cathode: which are low in reactivity series (less capability of forming ions more power to be reduced or better oxidising agents) those are discharged at cathode
for anode: which have more concentration

At the cathode, its not the ones that are low in reactivity series (I'm not sure abt ths), but low in discharge series.. as in if the discharge series are written horizontally: For eg: X and G: the discharge series would be:
X > F >L > G this means that X will be discharged preferentially than G because it's lower or its behind G in the discharge series.
At the anode, you're right But please tell me if i am wrong..

 

[knowitall10]

Another question:
"Solubility product is the product of concentrations of each ion in a saturated solution of a sparingly soluble salt at 298K, raised to the power of their relative concentrations"
Can someone please explain this definition?

 

[1357913579]

Jazak Allahu Khair Brother.
What I'm saying is that my book states "when using graphite electrodes". so when electrolysing aq solutions, do we only use graphite electrodes, or any other inert electrode like platinum?

Graphite is it self inert electrode so u can use that for electrolysis BUT for some electrolysics such as that of Brine(Nacl) for that there are specific electrode that could be because they must be more suitable for that experiments their are always exceptions.
plus if your talking about electrode while measuring electrode potnetial then u MUST know that we use the electrode of the same material of which the solution like for electrolyte of copper solution we use copper electrode EXCEPTIONS here are if there is a gas or ions of the same element in different oxidation states in these 2 cases we ussually use platinum electrodes although there are very expensive.

 

[1357913579]

At the cathode, its not the ones that are low in reactivity series (I'm not sure abt ths), but low in discharge series.. as in if the discharge series are written horizontally: For eg: X and G: the discharge series would be:
X > F >L > G this means that X will be discharged preferentially than G because it's lower or its behind G in the discharge series.
At the anode, you're right But please tell me if i am wrong..

isnt hydrogen low in reactivity series then Na(sodium) and it gets dicharged then Na but Copper gets discharged preferentially then Hydrogen because its lower in reactivity series then hyrogen isnt it??

 

[knowitall10]

Graphite is it self inert electrode so u can use that for electrolysis BUT for some electrolysics such as that of Brine(Nacl) for that there are specific electrode that could be because they must be more suitable for that experiments their are always exceptions.
plus if your talking about electrode while measuring electrode potnetial then u MUST know that we use the electrode of the same material of which the solution like for electrolyte of copper solution we use copper electrode EXCEPTIONS here are if there is a gas or ions of the same element in different oxidation states in these 2 cases we ussually use platinum electrodes although there are very expensive.

hmmm..thanks a lot!
That helped.... so, that discharge series i uploaded the photo of, does that only apply to graphite electrodes, or any electrode?

 

[1357913579]

if u need more explantion at that then see
Copper + NaOH-----> no reaction because Nais more reactive then copper so hydrogen remains as atom and leaves the solution gets discharged
now
H2 + Cu(OH)2 -----> there will be a reaction and A copper ATOM Cu will get dischared at the cathode becuase it lower in reactivity series then hydrogen

 

[knowitall10]

isnt hydrogen low in reactivity series then Na(sodium) and it gets dicharged then Na but Copper gets discharged preferentially then Hydrogen because its lower in reactivity series then hyrogen isnt it??

The reactivity series has nothing to do with ion discharge, Brother. It's their Electrode potential values. Hydrogen is discharges instead of copper because it has a more positive electrode potential.

 

[1357913579]

The reactivity series has nothing to do with ion discharge, Brother. It's their Electrode potential values. Hydrogen is discharges instead of copper because it has a more positive electrode potential.

sorry iam having some internet connection problems
see what ut saying regarding electrode potential is RIGHT but thats the other way using reactivity seires IAM sure about i mentioned that becuase u mentioned concentration becuase these are 2 ways we use to use when we were not introduced to using electrode potential