Why is it that NaCl and MgCl2 are both shown as acidic with different indicators but they are actually neutral?

Answer 1

Beats the snot out of me. Because you're using a crappy indicator? Because you're using crappy water?

Okay, so I can explain magnesium chloride: it's because hydrochloric acid is a strong acid and magnesium hydroxide is not very soluble, making it a weak base.

However, sodium hydroxide is a strong base and NaCl solution should be as close to neutral as makes no never-mind, provided you didn't start with water that was already acidic to begin with.

It's also possible that the indicator that you're using goes to the "acidic" color a little above pH 7, so true neutral solutions test as "acidic" even though they're not.

Answer 2

NaCl and MgCl2 are both strong electrolytes that dissociate into ions in water. While the chloride ions can interact with water and change the pH, the cations sodium and magnesium do not affect pH significantly. Therefore, overall, the solutions of NaCl and MgCl2 are neutral despite showing acidic behavior with certain indicators.