Insti of Chemy, Univ of the Phili, Dili, QC

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Dept of MolBio and Biotech, CS, Univ of the Phili, Dili, QC

ABSTRACT

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The objectives of the experiment are to use the analytical balance correctly, to gain an understanding of some concepts of statistical chemistry, and to apply statistical concepts in analytical chemistry. The experiment preceded by ten teams weighing ten 25-centavo coins using an analytical balance, weighing by difference. After doing the calculations to analyze the data, some of the values were rejected from their data sets. Overall, the results of the calculations denote that the data values gathered have high precision since the pooled standard deviation is low. The experiment shows that in order to analyze data properly and objectively, one must apply statistical concepts. -------------------------------------------------

Introduction

All measurements are subjected to random errors. Sometimes, data can be either accepted or rejected before they are further analyzed. This is done by calculating the Q-test ( [1]). Computing for the confidence limit ( [2]) in 95% confidence level provides the range where the true value lies. Precision refers to the degree of reproducibility of a measures quantity, or the closeness of agreement when the same quantity is measured several times. Precision is high when the measurements deviate by only a small amount from the average; it is low if there is wide deviation. Precision in the data can be analyzed by performing calculations, including: computing for the mean or average ([3]) which provides an estimate of the true value; computing for the standard deviation ( [4]), the square root of variance, the measure of scatter of random error; computing for relative standard deviation in parts per million ([5]); computing for the range ( [6]); and computing for the relative range in parts per million ([7]). In addition, the pooled standard deviation ( [8]) for all the data of all the groups was also computed. The purposes of the experiment are to be able to train the students to use the analytical balance properly, to make the students understand some concepts of statistical analysis, and to make the students apply statistical concepts in analytical chemistry. Experimental Detail

The experiment involves ten teams weighing ten 25-centavo coins using an analytical balance. The procedure used in weighing was by difference, which involves weighing the samples with the beaker or watch glass where the samples were placed numerous times, each time a part of the sample (in this case, a coin) is removed. After all the data were recorded, they were analyzed by performing calculations, including the Q-test (for the acceptance or rejection of values), mean (average), standard deviation (square root of variance), relative standard deviation in parts per million, range, relative range in parts per million, and the confidence limit (range where true value lies). Results and Discussion

In the set-up done, the data gathered are as follows: for Set1 (mass of the six coins), 3.6030g, 3.7920g, 3.6140g, 3.6150g, 3.6700g, and 3.6330g. For Set2 (mass of the ten coins), the same values with an addition of 3.6290g, 3.5790g, 3.5970g, and 3.7970g. Table 1. Data gathered in set-up

Sample No.| Weight, g|

1| 3.6030| Data Set2| Data Set1|

2| 3.7920| | |

3| 3.6140| | |

4| 3.6150| | |

5| 3.6700| | |

6| 3.6330| | |

7| 3.6290| |

8| 3.5790| |

9| 3.5970| |

10| 2.7970| |

In performing the calculations for the analyzing the data, results in the Q-test showed that the value 3.7920g should be rejected in the data Set1, for its Qexp (with a value of 0.646) has a higher value compared to the tabulated Q (with a value of 0.625).

Table 2. Results of...