Community College Of Philadelphia Department Of Chemistry

Community College Of Philadelphiadepartment Of Chemistrychem 101 Dista

Community College of Philadelphia Department of Chemistry CHEM 101 Distance Course Laboratory Report Sheet Name: Date: Email: Laboratory Instructor: Course Nbr.: CHEM 101 Distance Section: Experiment Nbr.: 1 – Home-based Lab Experiment Title: LABORATORY MEASUREMENT Purpose: Concepts related to the textbook: Conclusion: Experiment 1 – LABORATORY MEASUREMENT The following is to be completed at home. For background: · Read the information on significant figures and dimensional analysis in your textbook. Some of the measurement techniques described in your manual may be done at home with varying degrees of accuracy, while others will need to be done in the laboratory where the needed instruments are available.

You will also see most of these measurement techniques and instruments in the demonstrations that appear in the videotapes. The purpose of this experiment is to familiarize you with the proper way to take and record measurements using a meter stick (ruler). Additionally, it is to help you learn to apply significant figure rules when combining measurements and to learn what is implied by and what the difference between precision and accuracy is. In this experiment, all the numbers in parentheses refer to lines on the attached data sheet where your measurements and/or answers are to be recorded. I.

AREA OF A RECTANGLE Use the rectangle below to do the following measurements. A B C D Using a ruler, measure and record (1) the length (line AB) and (2) width (line AC) of the rectangle drawn above in cm . Be sure to record the measurement as accurately as possible in order to attain the maximum number of significant figures. Record these lengths to 2 decimal places, e.g., 1.20 cm. For example, some line might be 8.55 cm....that means, the line ended between the calibrated (marked) 8.5 and 8.6 lines on your ruler...... and you estimated its very end to be closer to the 8.6 and therefore estimated the next/last number.........and recorded the measurement to be 8.55 cm.

If a line ended exactly on the 8.6 calibration, you would record 8.60 cm. You will recall that the area of a rectangle is equal to the length times the width (A=LW). Use your calculator and the formula given to find the area of the rectangle (3). Record all the digits provided by your calculator. Note that cm x cm = cm2; the units of area are always a squared unit.

Record the area (4) rounded to the proper number of significant figures based on your original measurements. In science, it is often necessary to report or use a measurement in units other than that in which it was originally recorded (conversions). In order to practice this type of conversion: Show the set-up (5) to convert the area of this rectangle from cm to m . [Recall that 100 cm = 1m. Therefore, (100cm) = (1m) or 10000cm = 1 m ]. Convert the value to square meters and report the area (6).

Report the area one final time using scientific notation (and the correct number of significant figures) (7). As an additional practice, suppose a student had measured the length and width of a different rectangle in inches and had calculated the area as 150 square inches. What would the area be in square feet? (8) [Recall that 12 inches = 1 foot. Therefore, (12 inches) = (1 foot) or 144 in =1ft .] Convert this area from square inches into square centimeters (2.54 cm = 1inch) (9). Be certain to report the result to the proper number of significant figures.

II. AREA OF A TRIANGLE Area of triangle = one-half x base x height or A=1/2 bh A B D C You are going to calculate the area of this triangle using two different sets of measurements. The point is to show that the resulting calculation of area depends on the precision with which you take the original measurements and effects the final calculation. The application of significant figure rules to the results of calculations is supposed to prevent these discrepancies! Let’s see if it does.

Use the ruler provided (10). In the first set, record the length of the base “ABC†and its height “DB†in cm. In the second set, record the length of the base “DC†and its height “AD†in cm. Calculate the area of the triangle in square centimeters in each case. First, record the area answers using all the digits provided by your calculator and then rewrite the calculated area answers using the significant figure rules.

How do the values of the original calculator areas compare: Are they exactly the same before rounding/applying significant figure rules, yes or no (11)? If NO, explain why not (12). Are the 2 original calculated areas close or very different (13)? After rounding to the proper number of significant figures, are the two answers for the area of this triangle the same (yes or no)? (14) III. PRECISION AND ACCURACY Use your textbook or a dictionary for reference, if necessary.

This topic is also discussed on the World of Chemistry #3 videotape. What is meant by the precision of a set of measurements (15)? What is meant by the accuracy of a set of measurements (16)? Suppose a student determined a certain triangle to have an area of 26.5 cm2 by one set of measurements and 26.7 cm2 by a second set of measurements and 26.8 cm2 by a third set of measurements. What is the average (mean) value of these three areas (17)?

By comparing the 3 individual areas to the mean/average, how would you describe the student’s precision (18) and accuracy (19)? IV. MEASUREMENT Units of measurement are a means of communication. What things do you measure every day, in the kitchen, bathroom, workplace, etc.? List at least 4 things (20).

How do you know that the scale at the grocery store is accurate or that the pump at the gasoline station measures the volume accurately (21)? Find an empty 1 or 2 liter bottle. (Soda is a common bottle found around the house). Fill your empty bottle with water. Using any measuring device that you have in your kitchen, measure the number of ounces equivalent to your bottle (22). (Recall that 1 cup =8 oz.)

Paper For Above instruction

Introduction

Accurate and precise measurements are fundamental to the scientific process. This experiment aims to familiarize students with proper measurement techniques using a meter stick, applying significant figure rules, and understanding the concepts of precision and accuracy. Through measuring the area of rectangles and triangles, students will explore how measurement precision impacts calculation results and how to properly report measurements in scientific notation and different units.

Body

Part I: Measurement of a Rectangle’s Area

The experiment begins with measuring the dimensions of a rectangle using a ruler, focusing on recording measurements with maximum significant figures. The length of side AB and width of side AC are measured in centimeters, with readings recorded to two decimal places. Calculation of the area involves multiplying these measurements, and the product is rounded according to the rules of significant figures.

Conversion of the area from square centimeters to square meters is conducted by setting up the appropriate conversion factors, recognizing that 100 cm equals 1 meter, so that 10,000 cm² equals 1 m². The same approach applies when converting from square inches to square feet, using the conversion factors 12 inches = 1 foot and 2.54 cm = 1 inch for length conversions. The calculation illustrates the importance of proper unit conversions and reporting in scientific notation for clarity and precision.

Part II: Measurement of a Triangle’s Area

The second part involves measuring the base and height of a triangle in two different sets of measurements, emphasizing how measurement quality affects calculated areas. The measurement of the base and height is in centimeters, and the area calculations are performed both with full calculator precision and subsequent rounding based on significant figures.

This assessment highlights potential discrepancies in measured areas depending on measurement precision, illustrating the importance of consistent significant figure application. The comparison between the two sets emphasizes the necessity of proper rounding for meaningful scientific reporting.

Part III: Understanding Precision and Accuracy

Definitions of measurement precision and accuracy are explored, referencing standard scientific definitions. The experiment explores how multiple measured values can be averaged to determine a mean area, and how consistency among measurements relates to precision, while closeness to true values reflects accuracy.

A hypothetical example with varying measured areas demonstrates how to evaluate a measurement set’s precision and accuracy, based on the consistency and proximity of measurements to a known or accepted value.

Part IV: Everyday Measurement and Unit Verification

This section discusses everyday measurement activities and methods of verifying measurement accuracy. Measuring household items such as bottles and using kitchen measuring devices reinforces concepts of measurement reliability. Comparing measurement results with known standards illustrates how to assess measurement accuracy in practical situations.

Conclusion

Accurate measurement and proper reporting are vital in scientific experiments. Understanding the significance of significant figures, units, and the concepts of precision and accuracy ensures reliable and meaningful scientific communication. Applying these principles during simple measurements such as area calculation and everyday tasks builds a solid foundation for more complex scientific investigations.

References

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