Titration lab help!?

Question

these questions are so hard for me to answer. Please help me.

Indicate how the concentration of the unknown monoprotic acid would be affected by each of the following errors. Circle the correct choice and briefly explain your choice.

a) air bubble in the buret during the entire experiment
decrease increase no effect
b) air bubble initially in the buret that disappears by the end of the experiment
decrease increase no effect
c) pH meter calibrated to read higher value than actual
decrease increase no effect
d) water left in pipet subsequently used to dispense acid solution
decrease increase no effect


Thanx

Answer 1

You don't really say, but I'm assuming that you had a standardized solution of something like NaOH that you used in the buret, and you used that solution to determine the concentration of an acid by titration. You also measured volumes of the acid for titration using a pipet.

OK...So, for a). If a bubble is present in the buret at the beginning of the experiment and it stays there the entire time, you shouldn't have any effect on your answer.

For b), if the bubble is not there at the end, then your buret reading will be off. The readings from your buret would indicate that you put more sodium hydroxide into the flask of acid than you actually did...Does that make sense? So, the concentration of your acid will actually be lower than your calculation says it is.

c) is more difficult for me to answer, since I'm not really sure whether you determined the end-point of yoru titration by going to a specific pH, or whether you looked at a graph of pH and volumes of base added to dettermine the equivalence point. If you did the first way, then your calculated result will be lower than your actual result. If you did it the second way, then it really should affect your result.

d) water in the pipet will dilute the acid as you dispense it, so that you are actually putting less acid in each titration than you should. So, your calculated answer will be lower than the actual concentration....

Hope this helps.