We did not use the volume of the water added initially to the Erlenmeyer in our calculations. Why?
Why do you think anything to do with the water is needed? It contains no moles of acid. It contains no moles of base. You are titrating acid with a base (or the other way around perhaps) and moles acid versus moles base is the only thing that matters, assuming the end point occurs where you want it to occur. My students always said to me, "but the water dilutes the stuff in the Erlenmeyer flask." And my response always was, "that is true but doesn't it dilute stuff added from the buret, also, and by the same amount?" Of course it does. The dilution explanation they usually understood, and it is true, but the REAL reason is what I wrote at the top of this discussion. The indicator knows where to change color in the acid/base relationship and the water has nothing to do with it except to give some volume to swish around in the flask.
Describe the apparent relationship between [H3O+1] and [OH-1] when the endpoint is reached in an acid-base
titiration.
When the endpoint is reached in an acid-base titration the apparent relationship between [H3O+] AND [OH-] they are equal.
Well, maybe someone spilled the water and we didn't want to make a big splash about it. Or maybe we just didn't want to water down our calculations. After all, it's already diluted enough!
When conducting experiments, it is important to consider the variables that could affect your results and to minimize their impact. In the case of using an Erlenmeyer flask, the volume of water added initially is not typically used in calculations because it serves as a known constant that does not change throughout the experiment. By not including it in the calculations, you can focus on the variables you are actually testing.
Here's an example to explain this further:
Let's say you are conducting an experiment to measure the solubility of a solute in water at different temperatures. You start by adding a fixed amount of water (let's say 100 mL) to an Erlenmeyer flask. Then, you add a known mass of the solute to the flask and stir until it dissolves.
During the experiment, you heat the flask to different temperatures while keeping the volume of water constant at 100 mL. After each temperature increase, you measure the mass of the solute that has dissolved.
In this case, you do not consider the volume of water added initially because it remains constant throughout the experiment. Your focus is primarily on the temperature as the independent variable and the mass of the solute dissolved as the dependent variable. By keeping the volume constant, you ensure that any changes in the amount of solute dissolved are solely attributed to the temperature and not the volume of water.
Excluding the initial volume of water from calculations helps to simplify the experimental setup and analysis, allowing for a clearer understanding of the relationship between the solute's solubility and the temperature.