CHEM 1602L Lecture Notes - Lecture 1: Standard Deviation, Observational Error, Pipette

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indigoraccoon343

6 Apr 2016

School

Vanderbilt University

Department

Chemistry

Course

CHEM 1602L

Professor

Phillips Shawn

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Document Summary

Accuracy describes how close a set of measurements is to the actual value of the measurement. When a set of measurements is accurate, this means that the average of these measurements is close to actual value. Precision determines how different measurements are close to each other. Precision can usually be determined by calculating the standard deviation of different sets of measurements, and the one with the least standard deviation is the most precise. In our experiment the results were the following: We can see by comparing the standard deviations is that the graduated pipette has the lowest standard deviation, hence is considered the most precise, and in our experiment, the most accurate, too. Systematic error produces poor accuracy. when the average of the results is not close to the actual result, this means that the way the measurements are done or the experiment is carried out is wrong or not perfect. There"s an error is the procedure not the reading.

Related Questions

Experimental outcomes in chemistry depend on making sound observations, taking precise measurements and accurately recording them directly in to the laboratory notebook. All experiments and therefore the results will contain errors (experimental error), which can adversely affect the reliability of the experiment and the credibility of the scientist. Experimental error is reduced when students master experimental techniques and become aware of which measurements have the most impact on the experiment in terms of accuracy and precision. Accuracy is determined by comparing the true or actual value to an individual experimental value or the average of many experimental values. If the true value is not given, the average of all the experimental values is assumed to be true value and accuracy is determined by comparing the average to the individual experimental values. Precision is a determined by comparing how close all the experimental values are to each other. The following data was collected by students in your laboratory section. Decide which value to you will use to complete the experimental calculations. The amount of error in your final experimental result depends on your decision. Each student used a different balance and weighed the beaker 4 times. The balances they used in the laboratory read to a hundredth of a gram. The results are shown below were recorded by each individual. What additional information about the students, instruments, and the conditions which the data was collected do you need to better of the evaluate the reliability of the experimental data? Give 1 and briefly (60 words or less, using complete sentences) explain your answer. Which set of data is the most precise? Show all equations and calculations. Briefly (60 words or less, using complete sentences) explain your answer. What student measurements are the least accurate? Briefly (60 words or less, using complete sentences) suggest how this student could improve their experimental techniques. Show all equation and calculations

Practice Problem Set 1

l. A common approach to calibrate a piece of volumetric glassware is to fill the glassware with water of at a known temperature and then we the water using an analytical balance. The "true" volume e water is then calculated using the density of the water at the recorded temperature. This process is repeated several times to get an average "true" volume of water and an error in the value,

You decide to perform such an experiment on a 10.0 mL volumetric flask, filling the flask to the mark with pure Dl water at 22 C five separate times and then weighing the water added by difference using an analytical balance. You obtain the following results with the analytical balance.

Exp 1 10,0163 g

Exp 2 10.0345 g

Exp 3 10.0558 g

Exp 4 10.0292 g

Exp 5 10.0484 g

Correct these masses for the buoyancy of air (use d 0.0012 g/cm and d 8.0 g/cm and then convert the corrected masses into volumes using the density of water at22 C given in Table 2-7

What is the average volume of water contained in the volumetric glassware and the error (standard deviation) this volume?

Is the glassware marking within the expected tolerance for a Class A volumetric flask?

ls the error reflected in the 5 experimental determinations a reflection of random error or systematic error?

) What is the systematic error revealed in this experiment?

Next you weigh out 0.5516 g of KHP (potassium hydrogen phthalate) and place it in the calibrated 2. 10.0 mL volumetric flask. You then fill the flask to the mark with 30 Cwater and swirl to dissolve the KHP

a) What is the concentration (M) of the resulting KHP solution (remember to correct the mass of KHP or the buoyance of air)?

b) What is the error in the concentration of the KHP solution?

c) Which measurement/device introduces the greatest error to the concentration calculation?

3. You decide to use the solution the next day and upon measuring the temperature of the solution, find that it has decreased to 20 C

a) What is the new concentration (M) of the KHP solution and the error in this value?

b) By how much in percent did the concentration of the KHP solution change from when you made it to when you used it?

CHEM 1602L Lecture Notes - Lecture 1: Standard Deviation, Observational Error, Pipette

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