# Why do acids mix in water faster than bases?

I have $100\ \mathrm{L}$ of water in a tank with an mixer inside and want to know how fast the tank mixes at a given rpm-setting. I am adding $50\ \mathrm{mL}$ of $2\ \mathrm{N}\ \ce{HCl}$ and see how long the $\ce{pH}$ goes to down to an equilibrium. Then I add $50\ \mathrm{mL}$ of $2\ \mathrm{N}\ \ce{NaOH}$ to the solution and wait for the $\ce{pH}$ to come to an equilibrium $\ce{pH}$. I feel like the 2 times should be the same, but acid mixes much faster than base in all cases. Why?

The time for $\ce{pH}$ to change from $7$ to $4$ is always less than time for $\ce{pH}$ to change from $4$ to $7$ in the same tank at the same rpm.

Any theories regarding why?

• How do you test the pH change? Also, what is "eve"? – SendersReagent May 5 '16 at 0:10
• pH probes are being used fr monitoring pH.. Not sure what you mean by "eve" .. RPM= rotations per min of the impeller/mixer – Suresh May 5 '16 at 11:24
• You had "eve" as one of your tags. It has apparently been edited out. If you were doing chemical analysis of pH, I would have guessed a slower base reaction than acid reaction. Don't know enough about pH meters to know if that's a possibility. – SendersReagent May 5 '16 at 11:34
• The analysis is slightly skewed. Please do the confirmation experiment of adding $50~\mathrm{ml}\ 2~\mathrm{M}\ \ce{NaOH}$ to $100~\mathrm{ml}$ of water and compare that time to adding $50~\mathrm{ml}\ 2~\mathrm{M}\ \ce{HCl}$. – Jan May 5 '16 at 12:03
• Could it simply be that you are adding 50 mls of acid to 100 mls of water and then 50 mls of base to 150 mls of solution? Time for mixing in a larger volume? Do as @Jan says, and time base into water, followed by acid into the solution and compare your times.. – Leeser May 5 '16 at 18:10