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Please help with questions 2 & 3

Please help with questions 2 & 3

Chemistry
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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Please help with questions 2 & 3
Chem 105 Online 1-Measurement of Physical Properties Part One: Using Chemical Equipment OBJECTIVES: To become acquainted with the various forms of chemical equipment. To determine which equipment provides the best accuracy and precision. INTRODUCTION Chemistry frequently requires the measurement of physical properties of compounds. Two of the most common measurements are mass and volume. During this experiment, we will use the top loading balance to determine mass to 0.01g sensitivity. Since these masses are experimental values, it is important to always record the balance reading to the full limit of its sensitivity. When taking measurements, it is important to distinguish between accuracy and precision. The precision of a numerical result is related to reproducibility, while accuracy is an expression of the uncertainty in the number (the amount of deviation from the "correct" or "real" number). Commonly, precision is related to random error (common unavoidable errors), while accuracy is dependent on both random and systemic errors (habitual error). 1. Determination of Percent Error of Various Volumetric Equipment In the first part of the experiment, a distinct volume of water will be measured with a 10mL graduated cylinder, a 100mL graduated cylinders, a 60mL buret and a plastic pipet. Each quantity of water will be weighed on the balance to measure the reproducibility and accuracy of the volume measurement. The density of water is temperature dependent and for example the mass of 10mL of water at room temperature will be about 9.94 to 9.98g. Thus water will have a mass very close to 9.96g for 10mL additions of water. For 25mL of water, it will have a mass of 24.85g to 24.95g. Therefore, we will use 24.90g as the accepted mass of 25mL additions of water To determine the deviation of a measurement from this value can be expressed as the percent error shown below. Accepted-Experimentall` Accepted % Error = (be sure to simply take the absolute value) Often I will describe this as "The difference between the two, all divided by the true" since the sign is an absolute value and we are looking for the overall deviation (either positive or negative) compared to the actual or accepted value. If the percent error is small, the measurements are accurate. If the percent error is constant for multiple data observations, the measurements have good precision. The 100mL graduated cylinder has low precision and low accuracy due to large random errors in the measurements. The scale on the cylinder is not designed to give high reproducibility, but is rather intended for quick, rough measurements. The 10mL graduated cylinder has better precision and accuracy than the 100mL g.c. but is still not intended for highly quantitative laboratory work. In contrast, the buret and pipet are designed to give good reproducibility (low random errors and high precision) and they will be accurate as long as their calibration is correct (no systemic errors). * 100%
Transcribed Image Text:Chem 105 Online 1-Measurement of Physical Properties Part One: Using Chemical Equipment OBJECTIVES: To become acquainted with the various forms of chemical equipment. To determine which equipment provides the best accuracy and precision. INTRODUCTION Chemistry frequently requires the measurement of physical properties of compounds. Two of the most common measurements are mass and volume. During this experiment, we will use the top loading balance to determine mass to 0.01g sensitivity. Since these masses are experimental values, it is important to always record the balance reading to the full limit of its sensitivity. When taking measurements, it is important to distinguish between accuracy and precision. The precision of a numerical result is related to reproducibility, while accuracy is an expression of the uncertainty in the number (the amount of deviation from the "correct" or "real" number). Commonly, precision is related to random error (common unavoidable errors), while accuracy is dependent on both random and systemic errors (habitual error). 1. Determination of Percent Error of Various Volumetric Equipment In the first part of the experiment, a distinct volume of water will be measured with a 10mL graduated cylinder, a 100mL graduated cylinders, a 60mL buret and a plastic pipet. Each quantity of water will be weighed on the balance to measure the reproducibility and accuracy of the volume measurement. The density of water is temperature dependent and for example the mass of 10mL of water at room temperature will be about 9.94 to 9.98g. Thus water will have a mass very close to 9.96g for 10mL additions of water. For 25mL of water, it will have a mass of 24.85g to 24.95g. Therefore, we will use 24.90g as the accepted mass of 25mL additions of water To determine the deviation of a measurement from this value can be expressed as the percent error shown below. Accepted-Experimentall` Accepted % Error = (be sure to simply take the absolute value) Often I will describe this as "The difference between the two, all divided by the true" since the sign is an absolute value and we are looking for the overall deviation (either positive or negative) compared to the actual or accepted value. If the percent error is small, the measurements are accurate. If the percent error is constant for multiple data observations, the measurements have good precision. The 100mL graduated cylinder has low precision and low accuracy due to large random errors in the measurements. The scale on the cylinder is not designed to give high reproducibility, but is rather intended for quick, rough measurements. The 10mL graduated cylinder has better precision and accuracy than the 100mL g.c. but is still not intended for highly quantitative laboratory work. In contrast, the buret and pipet are designed to give good reproducibility (low random errors and high precision) and they will be accurate as long as their calibration is correct (no systemic errors). * 100%
KIT 10mL graduated cylinder At Home Buret 150mL beaker 100mL graduated cylinder Plastic beral pipet Balance Distilled water PRELABORATORY EXERCISE: 1. Compare and contrast accuracy and precision. Accuracy is the measured valve Subtract the true value. Precision is how close repeated measurements Come to their average. The accurate vales have to be precise but the precise vales may or may not be accurate. 2. A student performs the experiment and acquires a mass of 9.25g for a 10mL addition of water. What is their percent error for this trial? 9.96-9.25g x100= 7.7 % error 9.25g 3. A student performs the experiment and acquires a mass of 25.28g for a 10mL addition of water. What is their percent error for this trial? 9.969-25.289 25.289 *100=-61 %error Documentation: In addition to your data sheet below being filled and post lab questions, all labs need to have a separate file of a single pdf (not individual uploads of pictures) as supporting evidence of your measurements. There are a couple of reasons you are being asked to do this: RO be 1. As a lab science class, you are expected to demonstrate mastery of equipment use. 2. I need to see that it is you doing to the lab. 3. I also need to provide feedback on your measurements compared to the actual reading. This is where significant figures come in. a. Be sure to use read feedback on submissions AND lab documentation to improve course performance. ***Lack of documentation will result in half earned credit the first time, the second offense will result in no points for that lab submission. *** 50- 2. 3. 4 !!! IMPORTANT 5
Transcribed Image Text:KIT 10mL graduated cylinder At Home Buret 150mL beaker 100mL graduated cylinder Plastic beral pipet Balance Distilled water PRELABORATORY EXERCISE: 1. Compare and contrast accuracy and precision. Accuracy is the measured valve Subtract the true value. Precision is how close repeated measurements Come to their average. The accurate vales have to be precise but the precise vales may or may not be accurate. 2. A student performs the experiment and acquires a mass of 9.25g for a 10mL addition of water. What is their percent error for this trial? 9.96-9.25g x100= 7.7 % error 9.25g 3. A student performs the experiment and acquires a mass of 25.28g for a 10mL addition of water. What is their percent error for this trial? 9.969-25.289 25.289 *100=-61 %error Documentation: In addition to your data sheet below being filled and post lab questions, all labs need to have a separate file of a single pdf (not individual uploads of pictures) as supporting evidence of your measurements. There are a couple of reasons you are being asked to do this: RO be 1. As a lab science class, you are expected to demonstrate mastery of equipment use. 2. I need to see that it is you doing to the lab. 3. I also need to provide feedback on your measurements compared to the actual reading. This is where significant figures come in. a. Be sure to use read feedback on submissions AND lab documentation to improve course performance. ***Lack of documentation will result in half earned credit the first time, the second offense will result in no points for that lab submission. *** 50- 2. 3. 4 !!! IMPORTANT 5
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