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Current Ionic Solution, Charges

  • #1
191
0

Homework Statement



Current passes through a solution of sodium chloride. In 1.00 second, 2.68*10^16 Na+ ions arrive at the negative electrode and 3.92*10^16 Cl- ions arrive at the positive electrode. What is the current passing between the electrodes? Final answer must be in milliamperes.

Homework Equations



I = Q / Δt

The Attempt at a Solution



2.68*10^16 Na+ (1.6*10^-19 C) = 4.288 ma
3.68*10^16 Cl- (-1.6*10^-19C) = -6.272 ma

4.288 ma + (-6.272 ma) = -1.984 ma

Why is this incorrect?
 

Answers and Replies

  • #2
157
0
The ions aren't traveling in the same direction.
 
  • #3
Borek
Mentor
28,404
2,803
The ions aren't traveling in the same direction.
As far as I can tell OP accounted for that.

3.68*10^16 Cl- (-1.6*10^-19C) = -6.272 ma
Buy a new calculator.
 
  • #4
157
0
dQ/dt = I
opposite charges moving in opposite directions. Depending on the reference point both are either positive or negative.
Unless I'm missing something...
 
  • #5
Borek
Mentor
28,404
2,803
OP treats one current as positive, other as negative - that's equivalent.

And there is a simple math mistake in the final summation.
 
  • #6
157
0
I don't see how that is equivalent since they are moving in opposite directions.
Say you have two charges one at point A and one at point B with one being positive and one being negative.
If they both move to opposite points then the magnitude dQ is 2. I don't see why this problem is different.
 
  • #7
Borek
Mentor
28,404
2,803
Sigh, you are right. Call it a senior moment.
 

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