ddsshin

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Dec 6, 2006
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Dental Student
For T1 68
why NAOH -> NA + OH is wrong
why Ba(OH)2 --> Ba + 2OH is wrong
both of them are in aqu. solution.

T2 68
I get to the point where x = 0.4 + 0.01X and I get X= 0.404
how is this 40.4 ml? shouldn't this be 404ml ??? not sure....

T1 52
PbO+ CO2 --> Pb + CO2
which is oxidizing agent? and which is reducing agent why??
 

joonkimdds

Senior Member
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7+ Year Member
Jun 30, 2005
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Pre-Dental
For T1 68
why NAOH -> NA + OH is wrong
why Ba(OH)2 --> Ba + 2OH is wrong
both of them are in aqu. solution.

T2 68
I get to the point where x = 0.4 + 0.01X and I get X= 0.404
how is this 40.4 ml? shouldn't this be 404ml ??? not sure....

T1 52
PbO+ CO2 --> Pb + CO2
which is oxidizing agent? and which is reducing agent why??
I don't have topscore so here are just my guess.
NaOH dissolves into Na + OH
but if it's in aqu. solution i think you should think about the next step which is
Na + OH + H + OH --> NaOH + H2O. LOL what am I doing...:oops:

68, tell me what the problem is and I will do it.

Pb from PbO must be +2 because O is -2.
It becomes zero when it becomes product becuz it's by itself.
Thus it moves from +2 to zero. Number decreased thus reduction occurred to Pb. This also means Pb is an oxidizing agent.

C from CO2 must be +4 because O is -2 and there are two of them which is -4.
and then....what the heck? LOL this is not balanced :oops:
 
Last edited:

sakz

10+ Year Member
Mar 13, 2009
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Pre-Dental
for topscore 1, #68

NaOH --> Na+2 + OH-
Ba(OH)2 --> Ba+ + 2OH-

the charges on the Na and Ba are wrong

#52

PbO + CO --> Pb + CO2

PbO is the oxidizing agent b/c it is being reduced. goes from +2 to 0
therefore CO2 will be the reducuing agent/oxidized

TS 2/ #68

you found x to be .4 which is the amount of extra HCl you need to add. so the total volume will be 40.4 mL (HCl + base). since we are finding just the amount of HCl put in, subtract it be 20 ml (the base) and we get 20.4.

i took this test today and i figured i rounded weird somewhere so put 20.2 and got it wrong...

hope this helped