Question

A.) During titration, a student adds water to the beaker with the acid. Will this affect the measured equivalent mass? If so, how?

B.) What if he pulls the pH electrode (with solution on it) and rinses it off into a waste container before replacing it. Will this affect the measured equivalent mass and if so, how?

Answer 1

a)

Diluting the solution in the beaker ( that is adding water) will have no effect on the titration result - Therefore it will have no effect on the final calculated molar or equivalent mass. The quantity of acid in the beaker that you are titrating is not changed by the addition of water.

b)

trivially. When you do a titration, you force the neutralization of acid with base. Each ion has to match up with its opposite equivalent, and then you calculate how much of the one had to be present based on how much of the other you had to add. Obviously, if you remove some of the original mass, there will be less total number of the target ion remaining. But unless the solution has a very small relative volume, the mass loss will be difficult to identify; it will be proportionally tiny and generally smaller than the error in measurement. But you would have changed the total mass that was in the solution by removing part of the solution.

It is somewhat like taking a bucket of water from a lake: the total mass of the lake has decreased. But when dealing with a lake (rather than a mud puddle) the loss is not measurable. So whether the removal and rinsing of the pH probe matters (can be identified or observed or measured) depends on whether you are dealing with the equivalent of a puddle or a lake.