Chemistry Lab

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Making Measurements INTRODUCTION Chemistry is an experimental science. When gathering information in an experiment the data often involves quantitative, or numerical, measurements. It is important to learn how to make and use these measurements properly. In this lab, you will learn how to correctly make measurements involving mass, length, volume, and temperature. Units The units used are from the metric system. The unit of length is the meter (m); of volume, the liter (L); of mass, the gram (g); and of temperature, degrees Celsius (oC). In the metric system the unit is made larger or smaller by adding prefixes, such as centi- and kilo- (with the exception of temperature). Making Measurements Some equipment used for making measurements has marks on the equipment that indicate the value of the measurement. When making measurements it is important to be as precise as possible. In lab you will record the digits shown on the measuring device plus one estimated digit. The last digit will be determined by estimating the distance between the smallest increments on the marked scale. The final digit represents the best guess about where the object falls relative to the markings on the instrument and is always the least certain digit. The estimated digit tells us how close we are to the smallest marking we can read. When making our measurements, we always estimate one digit past the smallest marked increment. Example 1:

Suppose we are measuring the length of the red line in the image above. The ruler has numbered markings in the ones place. When making the measurement, the known value for the centimeter is 2 cm. Between 2 cm and 3 cm there are 10 lines. That means each line represents 0.1 cm. The red line is between 0.3 and 0.4 (between the 3rd and 4th lines). With certainty the measurement is 2.3 cm. To make the most precise measurement the last digit is estimated. In this case, the estimated digit will be to the 0.01 place. Because the line falls just before the halfway between the two markings, the estimated digit could be 0.04, giving a recorded measurement of 2.34 cm. Summary: the ruler has marked lines to the tenths place, so the estimated digit would be in the hundredths place.

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Example 2:

Suppose we are measuring temperature using the thermometer in the picture. The thermometer has numbered markings in tens place of oC. Between 0oC and 10oC there are 10 lines. That means each line represents 1oC. The blue liquid is between 2oC and 3oC markings (between the 2nd and 3rd lines). With certainty the measurement is 2oC. To make the most precise measurement, the last digit is estimated. In this case, the estimated digit will be to the 0.1 place. Because the line falls just before the 3rd mark, the estimated digit could be 0.8, giving a recorded measurement of 2.8oC. Summary: the thermometer has marked lines to the ones place, so the estimated digit would be in the tenths place. Example 3:

10-mL graduated cylinder 100-mL graduated cylinder Let’s look at two different graduated cylinders for comparison. The graduated cylinder on the left is a 10-mL graduated cylinder and the cylinder on the right is a 100-mL graduated cylinder. When measuring the volume of a liquid, read the meniscus of the liquid (the lowest part of the curve) at eye level. 10-mL graduated cylinder: The cylinder has numbered markings in one’s place of mL. Between 9mL and 10mL there are 10 marking lines. That means each marked line represents 0.1mL. The meniscus of the water is between 0.6 mL and 0.7 mL. With certainty the measurement is 9.6 mL. To make the most precise measurement, the last digit is estimated. In this case, the estimated digit will be to the 0.01 place. Because the line falls just before the 7th mark, the estimated digit could be 0.09, giving a recorded measurement of 9.69 mL. Summary: this 10-mL graduated cylinder has marked lines to the tenths place, so the estimated digit would be in the hundredths place.

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100-mL graduated cylinder: The cylinder has numbered markings in tens place of mL. Between 10mL and 20mL there are 10 marking lines. That means each marked line represents 1mL. The meniscus of the water is right on the 21 mL marked line. With certainty the measurement is 21 mL. To make the most precise measurement, the last digit is estimated. Because we know the measurement to the ones place, the estimated digit will be 0.1 place. In this case, where the measurement falls on a marked line, the estimated digit could be 0.00, giving a recorded measurement of 21.0mL. Summary: this 100-mL graduated cylinder has marked lines to the ones place, so the estimated digit would be in the hundredths place. In the event the estimated digit is on the line, use 0 as the estimated digit. Some equipment used for making measurements is digital. When using digital equipment to make a measurement, record all of the digits presented. You do not round or add to the digits shown on a digital device. The digital scale below is an example of a digital instrument.

Making and recording measurements in science is fundamental. Scientists communicate ideas and come to conclusions through measurements. It is important to represent these values to the best of our ability.

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Measurements Activity: In this lab we will be measuring volume, length, and temperature. Prepare your notebook. When the lab is complete your lab notebook should include the following:

1. Include Measurement Lab in the Table of Contents 2. Write the title of the lab on the top of the page. 3. Date/number the page (if you work on it over a few days, date each time you are

working). Sign in your lab notebook each time you stop working. 4. Record the Purpose of Experiment in your own words. Remember the purpose is the

overall question that will be answered by collecting the data and doing any requested calculations.

5. Indicate PPE (personal protection equipment) required while performing the lab: goggles, closed-toed shoes

6. Complete the measurement practice below. Record ANSWERS ONLY in your notebook.

7. Copy the four tables in the Procedure in your notebook. 8. Complete the Post-lab questions. Record ANSWERS ONLY in your notebook.

Measurement Practice: For each of the following, record the measurement. Remember to include the estimated digit and the units. gram (g) scale

Centimeter (cm) scale

Celsius (oC) scale

Procedure: Remember to make all measurements to the correct precision Materials/Equipment needed: 10-mL graduated cylinder Beaker 25-mL graduated cylinder Ruler 100-mL graduated cylinder pipet Thermometer water

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The purpose of this experiment is to introduce several common pieces of glassware and to illustrate why one piece of glassware maybe preferred for a particular measurement. A. Measuring Volume using three different graduated cylinders

1. Examine the beaker and the three graduated cylinders you have. What value do the smallest marks represent? For example, do the smallest marks (the lines between the numbered lines) on the scale represent 5mL, 1mL, 0.5mL, 0.2mL or 0.1 mL? In your notebook, record the value of the smallest marking on each in Table 1.

Table 1. Precision of glassware Glassware Value of smallest marks beaker 100 mL graduated cylinder 25 mL graduated cylinder 10 mL graduated cylinder

2. Use the pipet to add 9 mL of water as carefully as possible in the beaker. Record 9 mL in Table 2. You will be estimating 9mL because there is no mark for 9 mL, only 10mL and 5 mL.

3. Pour the water from the beaker into the 100-mL graduated cylinder. Measure the volume and record the volume to the correct precision in Table 2.

4. Pour the water from the 100-mL graduated cylinder into the 25-graduated cylinder. Measure and record the volume to the correct precision in Table 2.

5. Pour the water from the 25-mL graduated cylinder into the 10-mL graduated cylinder. Measure and record the volume to the correct precision in Table 2.

Table 2. Measuring Volume Measurement + unit beaker 100-mL graduated cylinder 25-mL graduated cylinder 10-mL graduated cylinder B. Measuring Temperature using a oC thermometer

1. Measure the room temperature. Fill a beaker with water and let it sit on the counter for 15 minutes. Place the thermometer in the beaker with water. Measure to the correct precision and record the temperature once the liquid in the thermometer stops moving.

2. Measure the temperature of ice water. Add ice to the beaker with water. Place the thermometer in the beaker with ice water. Measure to the correct precision and record the temperature once the liquid in the thermometer stops moving.

Table 3. Measuring temperature Measurement + unit Room temperature water Ice water

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C. Measuring length using a ruler

1. Measure to the correct precision and record the length of the line below, using the metric ruler.

2. Measure and record the length of the same line using inches

Table 4. Measuring length Measurement + unit Line 1 (metric) Line 1 (English) Post-Lab questions Answer the following questions in your lab notebook

1. When taking a measurement, how do you determine the last digit in the number you report?

2. When using a graduated cylinder, the liquid often curves up along the sides of the container. Where along this curve should you measure the volume?

3. Explain why your measurement might not be identical to the measurements taken by your lab mates. Assuming all the measurements were taken correctly, what is the maximum number of digits that should differ between your measurement and those of your lab mates?

4. When measuring a small volume, such as the volume of a small test tube, which size graduated cylinder should you use to obtain the most precise measurement. Explain your choice.

5. Give an example when a beaker might be a good choice for determining a volume of a liquid.

6. What would be a limitation when using the lab thermometer? Was the temperature of the ice water what you expected?

7. What the advantages of using the metric system. Use the measurements made for length to support your answer.

Works cited: Mullins, N.J., & Milczanowski, S.E. (2020). Lab Manual for Introductory Chemistry CHM1025C/CHM 1032C. Jacksonville: FSCJ Copy Center