Colorimetric Analysis Lab Report

Does a Measurement Result in a True Value? Limitations of Measurements
Elizabeth Lechtholz-Zey & Marisa Loredo
10/5/15
CHEM 101-08

Purpose To determine the differences in precision and accuracy in weighing 10 mL of water using a 50 mL beaker, a 10 mL graduated cylinder, and a 50 mL buret.

Data
Temperature of water: 23.0ºC
100 mL beaker weight: 50.557 g

# of additions of water to the 100 mL beaker * 50 mL beaker
(±5 mL) * 10 mL graduated cylinder (±0.05 mL) * 50 mL buret
(±0.05 mL)
0 0.00 g 0.00 g 0.00 g
1 7.48 g 9.91 g 9.95 g
2 14.23 g 19.70 g 19.83 g
3 21.38 g 29.56 g 29.85 g
4 29.20 g 39.44 g 39.77 g
5 35.91 g 49.30 g 49.72 g

* 10 mL graduated cylinder
(±0.05 mL)
0 50.557 g
1 60.340 g
2 70.010 …show more content…
For example,
S=√(〖∑▒〖(x-x ̅ ̅ 〗)〗^2/(n-1) □(⇒┬ )) √((〖∑▒〖((7.50-7.20〗)〗^2+〖(6.77-7.20)〗^2+〖(7.17-7.20)〗^2+〖(7.84-7.20)〗^2+〖(6.73-7.20)〗^2)/(5-1) )
S=√(0.906/4)=0.48 g/〖cm〗^3=0.48 mL Water added by 50 mL beaker Water added by 10 mL grad cylinder Water added by 50 mL buret
Average volume (mL) 7.20 mL 9.88 mL 9.96 mL
Standard deviation (mL) 0.48 mL 0.044 mL 0.060
Absolute error for glassware (mL) 2.8 mL 0.12 mL 0.04 mL
Relative error for glassware (%) 28.0% 1.2% 0.4%
Relative standard deviation for glassware (%) 6.7% 4.5% 0.60%

The absolute error shows the accuracy of the experimental error compared to the true value. Compare the amount of each aliquot to the average volume of each. An example of how to calculate this is shown below. error=X_true-X_experimental □(⇒┬ 10 mL-7.20 mL=2.8 mL)
To find the relative error, the following formula is used:
% error=(|X_true-X_experimental |)/X_true x 100%
(|10-7.20|)/10 x 100%=28.0%
To find the relative standard deviation, use the following