anonymous
  • anonymous
#1: A reaction in an electrolytic cell is as follows: 2NaCl (aq) + 2H2O (l) --> Cl2 (g) + H2 (g) + 2NaOH (aq). Which of the following reactions occurs at the cathode? A. 2H2O (l) + 2e- --> H2 (g) + 2OH- (aq) B. 2Cl- (aq) --> Cl2 (g) + 2e- C. H2 (g) + 2OH- (aq) --> 2H2O (l) + 2e- D. Cl2 (g) + 2e- --> 2Cl- (aq) ** no idea! :( @aaronq what do u think? :D
Chemistry
  • Stacey Warren - Expert brainly.com
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SOLVED
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katieb
  • katieb
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anonymous
  • anonymous
Try to identify oxidation and reduction reaction first.
anonymous
  • anonymous
the last one is anode right? (oxidation) ??
aaronq
  • aaronq
^ yep, use the reactions given to identify whats being reduced

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anonymous
  • anonymous
No, it is reduction reaction.
anonymous
  • anonymous
Oxidation is loss of electrons , and reductions always occur at cathode...
anonymous
  • anonymous
oh :/ I'm confused hahaha :( idk how to tell which is cathode tho :(
anonymous
  • anonymous
In the last reaction, there is gain of \(e^{-}\) so it is , reduction reaction.
anonymous
  • anonymous
You can learn the concept of electroplating on net, but here is the trick : Reduction always occur at cathode. Oxidation always occur at anode.
anonymous
  • anonymous
ohh i see.. so the answer to my problem is the last equation?? D ? :O
anonymous
  • anonymous
Yes, I think . @aaronq do you favor me ? that it is D. ?
aaronq
  • aaronq
hmm D looks like reduction reaction, but it's not whats written in the equation above 2NaCl (aq) + 2H2O (l) --> Cl2 (g) + H2 (g) + 2NaOH
aaronq
  • aaronq
Cl is actually being oxidized from -1 to 0
anonymous
  • anonymous
Yes. Agreed.
anonymous
  • anonymous
Look at A)
anonymous
  • anonymous
im confused haha :/ wait so its asking for which is taking place at the cathode.. :/ so it's not D? :/
anonymous
  • anonymous
A. 2H2O (l) + 2e- --> H2 (g) + 2OH- (aq) [Here is the removal of oxygen] - reudction reaction.
anonymous
  • anonymous
ohh okay so the answer to this is A then? :O
anonymous
  • anonymous
Wait iheartfood.
anonymous
  • anonymous
@aaronq , in the options given, only A and D are reduction reactions, right?
aaronq
  • aaronq
@Thoughts yeah, only A and D
anonymous
  • anonymous
kk :)
anonymous
  • anonymous
D - out, so left -- A
anonymous
  • anonymous
ohh okay!! :) awesome! thank you so much! :D
anonymous
  • anonymous
So it is A!
aaronq
  • aaronq
yep! @iheartfood do you know how to assign oxidation numbers?
anonymous
  • anonymous
awesome! :) ermm not really :/ how do i do that? :)
aaronq
  • aaronq
oh okay, because what would let you figure whats being oxidized and reduced easily (i.e. without guessing :P)
anonymous
  • anonymous
haha umm im gonna take a educated guess (its educated so its okay :P just for this tho :P ) and say that knowing how to assign oxidation numbers will help figure it out more easily? :D
aaronq
  • aaronq
hm there are basic rules, like everything in the first column is always +1 (e.g. Na) and everything in the second is +2 (Mg).. likewise everything in the 7th column is -1 (F), oxygen is always -2. the rest you have figure out by balancing the charges, wanna try some?
anonymous
  • anonymous
okay :) sure!
aaronq
  • aaronq
haha okay, do you know the periodic table (or have one handy)?
anonymous
  • anonymous
i can pull it out :)
aaronq
  • aaronq
okay, because you'll need it :)
anonymous
  • anonymous
kk its out :)
aaronq
  • aaronq
okay, easy one, what are the oxidation numbers of NaCl?
anonymous
  • anonymous
umm not too sure haha +3 ?
aaronq
  • aaronq
no okay remember the ones on the first column are always +1 (because they always lose only one electron) so Na = +1, right? now if the compound is neutral Cl must have a charge of?
anonymous
  • anonymous
-1 ?
aaronq
  • aaronq
yeah ! okay try MgO
anonymous
  • anonymous
+1 = Mg O=0 ?
aaronq
  • aaronq
hm no remember if the compound is neutral, the charges have to balance out. Now which group (column) is Mg in?
anonymous
  • anonymous
3?
anonymous
  • anonymous
oh oops i meant 2 :P
aaronq
  • aaronq
no thats row :P, groups are up and down
aaronq
  • aaronq
haha okay, so Mg is +2 because it's in group 2, right?
anonymous
  • anonymous
so it should be Mg= +2 O=-2 ?
anonymous
  • anonymous
mhmm :)
aaronq
  • aaronq
yes!
aaronq
  • aaronq
okay, what about H2O?
anonymous
  • anonymous
H= +1 O= -1 ?
aaronq
  • aaronq
oxygen is always -2.. and remember there are 2 hydrogens
anonymous
  • anonymous
ahh okay.. so it's H= +2 O= -2 ?
aaronq
  • aaronq
hm H = +1 but there are 2 right, so +1 x 2 = +2 so charges are balanced
aaronq
  • aaronq
OH^-
anonymous
  • anonymous
ahh i see :)
aaronq
  • aaronq
do OH^- !! lol
anonymous
  • anonymous
haha okay! :) erm O= -1 H=1 ?
anonymous
  • anonymous
not sure what to do with the - sign tho :(
aaronq
  • aaronq
nope! oxygen is always -2
anonymous
  • anonymous
oh right! my bad! so O= -2 H= +2 ?
aaronq
  • aaronq
H is always +1 :P
aaronq
  • aaronq
oxygen + hydrogen = -2 + 1 = -1 which is the charge on the ion
anonymous
  • anonymous
ohh okay :P
aaronq
  • aaronq
do NH3
anonymous
  • anonymous
kk N= - 9 ?? :/ H= +1
aaronq
  • aaronq
haha nooo why -9? 3 hydrogens = +1 x3 = +3 1 nitrogen = -3
anonymous
  • anonymous
ohh okay :P idk why lol :P
aaronq
  • aaronq
haha okay, few more: F2 (2 is a subscript)
anonymous
  • anonymous
kk :P F2=4 ?
anonymous
  • anonymous
after these i just have one more problem! :)
aaronq
  • aaronq
haha okay. what nooo, anything elemental like Al (s) or bound to the same element Cl2, is zero.
anonymous
  • anonymous
ohh okay.. so its just 0?
aaronq
  • aaronq
yes
aaronq
  • aaronq
same with all the noble gases, they're all zero
anonymous
  • anonymous
ahh okay :)
aaronq
  • aaronq
okay 2 more! Al(OH)3
aaronq
  • aaronq
OH is an ion that stays together, what is the charge on it?
anonymous
  • anonymous
kk :) ermm idk :( -2+1=-1 ?
anonymous
  • anonymous
Aaronq , nice teaching man. :)
anonymous
  • anonymous
agreed^^ :)
aaronq
  • aaronq
haha thanks guys !
anonymous
  • anonymous
:) i speak nothing but the truth :P
aaronq
  • aaronq
so the charge on OH is -1, is that what you said?
anonymous
  • anonymous
**typo :P I agree with nothing but the truth :P
anonymous
  • anonymous
yeah :) is that right? :)
aaronq
  • aaronq
haha okay okay you philosophers
anonymous
  • anonymous
hehee :P
aaronq
  • aaronq
so if there are 2 OH ions, what is the charge on Al to make it balanced?
aaronq
  • aaronq
i mean 3 OH ions
anonymous
  • anonymous
+3?
aaronq
  • aaronq
yeah ! are you getting it, or no? lol
anonymous
  • anonymous
yes :)
aaronq
  • aaronq
haha okay good, because now you have to do an equation: 2NaCl (aq) + 2H2O (l) --> Cl2 (g) + H2 (g) + 2NaOH
anonymous
  • anonymous
aww :( wowzers! kk lets see.. 2NaCl= +2 , -2 ? 2H2O = +2, -2 ?
anonymous
  • anonymous
Cl2= -1 x 2 = -2? H2= +1 x 2 = +2?
aaronq
  • aaronq
hm well, for NaCl, disregard the coefficient because you're assigning the oxidation number per species
aaronq
  • aaronq
ono remember anything attached to itself is zero? Cl2, H2, Br2, F2
anonymous
  • anonymous
OH= -1 ? Na= +1 ? okay, so NaCl= -1 +1 Cl2= 0 H2= 0 ??
aaronq
  • aaronq
yes! exactly. OH is -1 as a whole, but individually? H = ? O= ?
anonymous
  • anonymous
+1 -2
aaronq
  • aaronq
yes! okay just the last bit NaOH
anonymous
  • anonymous
kk :) Na= +1 OH= -1
anonymous
  • anonymous
?
aaronq
  • aaronq
yes! but technically you have to say that Na = +1 H= +1 O= -2
anonymous
  • anonymous
ohh okay :)
aaronq
  • aaronq
:) awesome, good job
anonymous
  • anonymous
thanks! :) kk posting the last one now! :P its all typed it.. clicking it... now!

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