Current in an Ionic Solution

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Homework Statement



Current passes through a solution of sodium chloride. In 1.00 second, 2.68 x 10^16 Na+ ions arrive at the negative electrode and 3.92 x 10^16 Cl- ions arrive at the positive electrode.

What is the current passing between the electrodes?
Express your answer in milliamperes to three significant figures.

Part B

What is the direction of the current?
~away from the negative electrode or
~toward the negative electrode

Homework Equations



I = Q/t

The Attempt at a Solution




the difference between 2.68x10^16 and 3.92x10^16 as a Na+ ion and Cl- ion carry precisely one electric charge each, and the charge of an electron is 1.60 x 10^-19 C

I = Q/t
I = (1.60 x 10^-19 )/1
I = 1.60 x 10^-19 A = 1.60 x 10^-16 mA

am I right?

Part B

Conventional current was defined early in the history of electrical science as a flow of positive charge, so it would be towards the negative electrode?
 

Answers and Replies

  • #2
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So for part A, the net positive charge would be q = Ne = (Cl - Na)e = (1.24x10^16)(1.6x10^-19) = 1.98 x 10^-3 and when I convert it to mA, I get 1.984, but it says it's wrong. Any ideas?
 
  • #3
ravi1611
how did u do dat ???? im really confused with dis question
 
  • #4
G01
Homework Helper
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You are correct with the direction of the current. Conventional current would flow toward the negative electrode.

For part a) I also get 1.984mA. You have said you want the answer to be in three significant figures, but 1.984mA has 4 significant figures. Could this be why it is being labeled as wrong? (I assume this is a computer based question?)
 
  • #5
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how did u do dat ???? im really confused with dis question

You are correct with the direction of the current. Conventional current would flow toward the negative electrode.

For part a) I also get 1.984mA. You have said you want the answer to be in three significant figures, but 1.984mA has 4 significant figures. Could this be why it is being labeled as wrong? (I assume this is a computer based question?)

I figured out the problem. I wasnt supposed to subtract the number of Na+ ions from the Cl- ions, I was supposed to add them together, and I would get 6.6 x 10^16 which I would multiply it by the charge of an electron, and once I convert it to mA, I get 10.6mA.

If the problem was too many significant digits, masteringphysics (the computer based website problem) would still give me the marks saying I just rounded it differently.

Thanks for everyone's help.
 
  • #6
G01
Homework Helper
Gold Member
2,682
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I figured out the problem. I wasnt supposed to subtract the number of Na+ ions from the Cl- ions, I was supposed to add them together.

AHHH!! Yes, I made the same mistake, don't feel too bad about it! Sorry if my mistake mislead you in any way.
 
  • #7
ravi1611
What quality must the charge density on the surface of a conducting wire possess if an electric field is to act on the negatively charged electrons inside the wire?

The charge density must be
positive.
negative.
nonuniform.
uniform.


can anybody plz help with dis..i think its uniform but im not sure
 
  • #8
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AHHH!! Yes, I made the same mistake, don't feel too bad about it! Sorry if my mistake mislead you in any way.

It's okay; I got the answer before you posted, and I'll prefer to do this on an assigment worth about 1% than a test any day

and ravi1611, the answer is nonuniform
 
Last edited:
  • #9
ravi1611
thx alot
 

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