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