[formulations4me]

I need some help calculating the confidence limit for KHP after titrating it with a standard NaOH. I have found the molarity of NaOH and the initial weight of the KHP needed. I can not seem to get the confidence limit right through propogation of error. The question is, Assuming no random error in the concentration of the titrant, calculate the 95 % confidence interval in the original sample weight which the student was given. Report to 3 significant figures.

Information that I know is right from my Excel worksheet:

Standardizing the NaOH:

average volume of NaOH, 19.56333333 ml
standard deviation of NaOH, 0.015275252
number of taken measurements = 3
molarity of NaOH, 0.129821159 moles/ml
weight of KHP, 5.1869g
fw of KHP, 204.23


Titrating the unknown:

0.01298 M of NaOH
25 ml KHP titrated
250 ml diluted volume
fw of KHP is 204.23
18.96333333 ml, average volume of NaOH titrating
0.005773503, standard deviation for titrating the unknown
n=3, number of measured quanities
grams of KHP found: 5.027819748

[Fridushka]

this will help you find the CI (look to the v:degree of freedom..)

[formulations4me]

Okay, thanks. I figured out what i did. I had the standard error and did not multiply it by the t-value.

[Fridushka]

You'r welcome..Good job