# Current Ionic Solution, Charges

## 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.

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?

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The ions aren't traveling in the same direction.

Borek
Mentor
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

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...

Borek
Mentor
OP treats one current as positive, other as negative - that's equivalent.

And there is a simple math mistake in the final summation.

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.

Borek
Mentor
Sigh, you are right. Call it a senior moment.