Edexcel CHEMISTRY DOUBTS!!!!

[Romeesa-Chan]

in part iii) the mass is 100,you have to use the mass\volume in cm^3 of the liquid\solution reacting.
ill take a look at the mark scheme and tell you if i got anything

Mass taken is 20g from HCl which was 20cm^-1.

[wakemeup]

Part c iii- I don't understand the mass calculation.
We used moles of Mg initially but then for temperature change, we used HCl. I don't get that.

Part civ I don't understand the time thingy.

I'm kind of confused here myself but I'm guessing we're taking the moles of magnesium in the calculation because the delta H is referring to one mole for the compounds and elements that are already one mole in the equation. So HCl can disregarded in the calculation. Again, I'm not 100% sure here.

Part iv is much easier. Take the time for 56C from the previous table and subtract 2 from it and then take the time for 10C and add 2 to it. Find theur inverse and then the ln of the inverse values. Now you can draw the graph and as we're considering ln1/T proportional to lnk, your gradient will be -Ea/R, according to y= mx+c so now you can find the new value of the activation energy.

Hope that helps.

[Romeesa-Chan]

I'm kind of confused here myself but I'm guessing we're taking the moles of magnesium in the calculation because the delta H is referring to one mole for the compounds and elements that are already one mole in the equation. So HCl can disregarded in the calculation. Again, I'm not 100% sure here.

Part iv is much easier. Take the time for 56C from the previous table and subtract 2 from it and then take the time for 10C and add 2 to it. Find theur inverse and then the ln of the inverse values. Now you can draw the graph and as we're considering ln1/T proportional to lnk, your gradient will be -Ea/R, according to y= mx+c so now you can find the new value of the activation energy.

Hope that helps.

For part vi, why do we add 2 for one value and minus 2 from the other?
That's what confused me.

[wakemeup]

For part vi, why do we add 2 for one value and minus 2 from the other?
That's what confused me.

They said in the question that there could be an error of 2 seconds and then told us to find the shortest time for one of the values (ie -2) and the longest time for the other value (ie +2)

[samriddh]

can anyone please tell me how to find a chiral center in cyclic molecules???
and ya do we have notes on organic chemistry esp chiral molecules and "hydrocarbons: fuels"
thank you for the help in advance!!

[iluvme]

Draw the hydrogen bonds around all the Carbons, that helps usually.

[Ghayth]

This E of cell stuff is really confusing ..
You have 2 reactions ,

Cu2+    +     e-    -----> Cu+      +0.15v
I2         +   2e-    -----> 2I-        +0.53v

Q) Calculate E of cell for the reaction.

What is wrong with what I am doing ?
I see that 0.15<0.53 so I deduce that Cu+ will be oxidised at the anode and I2 will be reduced at the cathode.
E of cell= Reduction - oxidation
E of cell= 0.53 - 0.15 = 0.39V
My notebook says that the E of the cell is - 0.39V :s

[Romeesa-Chan]

This E of cell stuff is really confusing ..
You have 2 reactions ,

Cu2+    +     e-    -----> Cu+      +0.15v
I2         +   2e-    -----> 2I-        +0.53v

Q) Calculate E of cell for the reaction.

What is wrong with what I am doing ?
I see that 0.15<0.53 so I deduce that Cu+ will be oxidised at the anode and I2 will be reduced at the cathode.
E of cell= Reduction - oxidation
E of cell= 0.53 - 0.15 = 0.39V
My notebook says that the E of the cell is - 0.39V :s

It gotta be +0.38V.

*Always make the more negative value the LHS (left hand side).

E cell= E (RHS) - E (LHS)

By the way, which textbook?

[Ghayth]

I know right ? 
Its not my text book , just my teacher's notes so I guess it was a mistake but thanks

[Romeesa-Chan]

I know right ? 
Its not my text book , just my teacher's notes so I guess it was a mistake but thanks

It happens. Must've been a mistake!
Good luck! (=

[abuelzouz]

hey people...how 's unit 5?

[Romeesa-Chan]

hey people...how 's unit 5?

It's fine. Just need to remember loads and practice the questions. It better be better than Unit 4. 

[abuelzouz]

It's fine. Just need to remember loads and practice the questions. It better be better than Unit 4. 

i thought unit 4 was good


nobody has doubts? lets share some stuyff

[Romeesa-Chan]

i thought unit 4 was good


nobody has doubts? lets share some stuyff

I might fail that paper.

Not at the moment. I might be posting later in the evening.

How's revision going?

[guMnam]

okay.. how does a benzene ring get deactivated ? i mean what groups or what ever deactivatesa benzene ring.. can somebody give me examples ?