# Charge, Size, and Movement in Aqeuous Ions as Electrolytes

Would a pair of aqueous $+2$ and $-2$ ions necessarily conduct electricity better than the same concentration of $+1$ and $-1$ ions? Furthermore, would more massive ions not conduct as well as less massive ions because they cannot travel as rapidly? It seems to me that ions move in the liquid to conduct electricity, because solid ionic crystals do not conduct electricity. If they move, then size and charge should both be factors affecting electrolyte strength. However, if ions are moving, why don't they ever achieve the most stable position and stop moving?

Would a pair of aqueous $+2$ and $−2$ ions necessarily conduct electricity better than the same concentration of $+1$ and $−1$ ions?

Not necessarily. Taking the concentration of 0.001 aqueous solution of $\ce{KOH}$ and $\ce{MgSO4}$ at $18$ degree Celsius, we find that the current conducted by $\ce{KOH}$ is $2.34 \space mA$ while the current conducted by $\ce{MgSO4}$ is $2.00 \space mA$. Why did this happen?

It happened because of the mass. And therefore here comes the answer to your second question.

Would more massive ions not conduct as well as less massive ions because they cannot travel as rapidly?

Yup, more massive ion means less current. It's because of simple equation (and I hope you are aware of these physics equations)$$qV=\dfrac{mv^2}{2}$$

Here $q$ is the charge on the ion. $V$ is potential difference between both the solutions. $m$ is the mass of the ion. And $v$ is the drift velocity. We know that $qV$ is constant. So we get $$v \propto \dfrac{1}{\sqrt{m}}$$ We can easily analyse that more the mass we have, less the speed we get.

If ions are moving, why don't they ever achieve the most stable position and stop moving?

They do achieve the most stable position and that's why batteries die.

• Hydroxide and hydrogen ions are special in water solution, as they have anomalously high mobility. This is due to 'hopping' mechanism en.wikipedia.org/wiki/Grotthuss_mechanism – permeakra Apr 30 '16 at 9:49
• But if you were sending a current through a solution, it could go on indefinitely. – Yunfei Ma Apr 30 '16 at 11:56
• @YunfeiMa You can take this scenario as recharging of battery. – manshu Apr 30 '16 at 12:08
• @manshu If I ran prepared a solution of say, NaCl, and continued to run current through it, would it stop conducting after a certain amount of time? – Yunfei Ma Apr 30 '16 at 14:52
• @YunfeiMa Yeah, at the time when the potential between the two electrolytes becomes 0, the conduction will stop. – manshu Apr 30 '16 at 14:54