Question

The goal of this experiment is to prepare an aqueous solution of sodium hydroxide and determine its concentration by titrating it with a solution containing a precise mass of potassium hydrogen phthalate KHC8H4O4 (abbreviated KHP). The reaction formula is: NaOH(aq) + C8H5KO4(aq) → NaC8H4KO4(aq) + H2O(l). This indicates that the ration of NaOH to KHP is 1:1 which means that 1mol KHP is equal to 1 mol NaOH. ​

A. Calculate the relative average deviation (RAD) for your standardized solution (in parts per

thousands).

B. Does a RAD measure accuracy or precision? Explain.

C. What goal was accomplished by standardizing these solutions?

D. How does the precision from this week effect next week’s results?

Answer 1

For example the titre values may be as follows,

TRAIL	CONCENTRATION(PPT)
1	56.08
2	56.04
3	55.95
4	56.23

A.The relative average deviation (RAD) can be= average deviation/average(X)

average deviation for the 4 trials =|X-Measurement 1|+|X-Measurement 2|+|X-Measurement 3|+|X-Measurement 4|/4

For the above trials,

Average(X)=(56.08+ 56.04+ 55.95+ 56.23)/4=56.075ppt

Average deviation={(56.075- 56.08)+(56.075- 56.04)+(56.075- 55.95)+(56.075- 56.23)/4

=0.08ppt

RAD=0.08/56.075

=0.0014

where, ppt stands for parts per thousand

B. If we dont know what the true value of a standardisation is, then we go with determining the precision of our measurement. RAD is the tool that can be used to check the precision of an experimental calculation. Here we will calculate the absolute deviation of each
measurement from the mean, average them, making the average deviation
relative by dividing with the average.

C. By the standardization of a solution the actual concentration of the prepared volumetric molar solution was known.

D. Precision is the measure for the closness of set values that you get by the experimental determination. It remain constant and the accuracy which is the realtiveness to the true value may change from week to week. So, there is no effect on precision.