CW 5: PRECISE Scientific Measurement Assn. 8

Every scientific measurement must include ALL the certain digits plus the first uncertain digit in the last place.

Each one of these digits counts as a significant figure.

Precise Measurement

Precise measurement on 10 ml graduate cylinder Precision of instrument = Uncertainty = Corrected uncertainty=

Precise measurement on 25 ml cylinder Precision of instrument = Uncertainty = Corrected uncertainty=

Precise measurement on 400 ml beaker Precision of instrument = Uncertainty = Corrected uncertainty=

Measurement on 350 ml cylinder Precision of instrument = Uncertainty = Corrected uncertainty=

CB4: Precise Scientific Measurements Background: All measurements are understood by the reader to include all the certain digits plus the first uncertain digit as the LAST digit in the measurement. These ARE the significant digits in the number.

When recording a measurement, scientists write the value of the numbered line ( 1 st certain digit), they count, then add, the value of the unnumbered lines (2 nd certain digit) and they estimate the amount of the measurement in between the lines (first uncertain digit). Include 0’s out to the first uncertain digit if a measurement is on the line.

Problem question: If the size of the scale gradations increases on an instrument, will the precision of the instrument increase or decrease or stay the same?

Hypothesis : If the size of the scale gradations increases on an instrument, then the precision of the instrument will _______ because__________________

Materials Different kinds of glassware Water

Procedure Calculate the precision of the instrument. Calculate the amount of uncertainty. Read the precise measurement of the liquid below the meniscus at eye level in the glassware. RECORD your measurement by reading the value of the numbered line, adding the value of the unnumbered line and estimating how much of the measurement is in the space. Calculate the precision of your measurements.

Fill in data table Kind of glassware Precision Of Instrument UncertaintyMeasureme nt of liquid Other member’s measureme nts Precision of your measuremt s 10 ml 25 ml 100 ml 150 ml 250 ml 500 ml 350 ml

Parts of Experiment Control group Experimental group Variables Constant Independent Dependent

Parts of Experiment Control group 10 ml grad. cylinder Experimental group all other glassware Variables Constant glass containers with marked scales Independent glassware with different scales Dependent size of scale

Make bar graph since these are discrete measurements. Dependent variable on the y-axis Independent variable on the x-axis

Make bar graph since these are discrete (separate entities) measurements. Dependent variable on the y-axis Independent variable on the x-axis

Results Statement

Conclusion Statement Compare results statement to hypothesis. (does it match? Why (what was your reasoning)? Why not? What is your new reasoning for these results? How accurate are your results? Why? Explain what could have introduced your error. What could you have done differently? What additional question could you explore to substantiate your thinking?

Sources of error Did you calculate the precision of the instrument so that you knew the value of the unnumbered lines? Was your last digit in your measurement the first uncertain digit? Do you have more than 1 uncertain digit in your measurement? Did you add a 0 to your measurement if it was on the line (you had 0 amount in the space)? Did you add too many 0’s where you did not have precision? Did you read the measurement below the meniscus? Did you read the measurement at eye level?

RESULTS questions on back of HW6 Assn The 10 ml graduate cylinder has the greatest precision because the space is smaller allowing a better estimate. The 350 cylinder has the least precision because the space is very large AND you are limited to the correct number of significant figures in the measurement.

2. As the size of the scale divisions gets bigger, the precision of the instrument decreases. 3. Skip 4. Calibration is knowing that the numbered and unnumbered lines actually represent the TRUE value==ACCURACY. (The balances are not calibrated, so that the same object will have a different measurement on each of the scales).

4. In order to draw lines on the cylinder that represent true values of volume, I would….

5. The volume of a liquid in a glass container is measured accurately by…. Reading below the meniscus at eye level

Measure out 100ml (or 50 ml) in a graduate cylinder and pour it into the large cylinder, the MARK where the liquid comes up on the cylinder. Repeat for every 100ml. I would not use a ruler to mark the sides of the cylinder!!!

6. Sources of error Did you calculate the precision of the instrument so that you knew the value of the unnumbered lines? Was your last digit in your measurement the first uncertain digit? Do you have more than 1 uncertain digit in your measurement? Did you add a 0 to your measurement if it was on the line (you had 0 amount in the space)? Did you add too many 0’s where you did not have precision? Did you read the measurement below the meniscus? Did you read the measurement at eye level?

Sources of error Calculate the precision of the instrument to COUNT their value to add to the numbered line. The last digit in your measurement must be the first uncertain digit (the amount of the measurement in the space; if NONE of the measurement is in the space you would have a 0 to show this). You have not included more than 1 uncertain digit in your measurement. ( Did you add too many 0’s where you did not have precision?). Did not read the measurement below the meniscus. Did not read the measurement at eye level.

7. The uncertain digit is estimated between the lines in the SPACE.

8. In a relationship question do NOT restate the question write it like the results statement!!!!! As the size of the scale division (gradation) increases, then the certainty will ____________.

Closure: Use your notes to find the best answers. 1.How does a scientist record a measurement precisely? ( 2 ways) 2. How is the precision of an instrument calculated? 3.What is the relationship between the size of the scale divisions (gradations) and the precision of an instrument? 4.How is the measurement of a liquid recorded with precision and accuracy in a glass graduated cylinder? 5.How does error in precision of a measurement occur by a person making the measurements on an instrument? 6.What is the difference between precision of an instrument and precision of a measurement?

Discuss the answers to these questions with the person in the row next to you:

1. How are all scientific measurements made precisely? (Include 2 ways from the Background/Research section of the lab). Find it. Mark it in margin. Read it. Discuss it with partner.

1. How are all scientific measurements made precisely? All measurements are understood by the reader to include all the certain digits plus the first uncertain digit as the LAST digit in the measurement. These ARE the significant digits in the number.

1. How are all scientific measurements made precisely? Read the numbered line, add the value of unnumbered lines, then estimate the amount of the measurement in the space. Include 0’s out to the first uncertain digit.

How is the precision of an instrument calculated? Directions below your data table. Find it. Mark it in margin. Read it. Discuss it with partner.

How is the precision of an instrument calculated? DIVIDE the difference between 2 consecutive numbers on the scale by the number of spaces.

What is the relationship between the size of the gradations and the precision of an instrument? From the RESULTS section under the graph.

What is the relationship between the size of the gradations and the precision of an instrument? As the size of gradations increases then the precision of the instrument decreases.

How is a glass graduated cylinder read with precision and accuracy? From the RESULTS section on HW 6

How is a glass graduated cylinder read with precision and accuracy? At eye level below the meniscus.

At eye level below the meniscus. The meniscus is the rounded bottom of the liquid that is viewed in a glass graduate cylinder because the glass causes a capillary action on the water that draws it up along the sides of the container.

A capillary tube is what is used in the doctor’s office to take a drop of blood from your finger or ear. The blood gets “sucked” into the tube by capillary action.

How does error in precision of a measurement occur by a person making the measurements on an instrument? From the Conclusion Statement in the lab.

How does error in precision of a measurement occur by a person making the measurements on an instrument? He does not calculate the precision of the instrument or he does not read below the meniscus at eye level, or he rounds the measurement up or down if he doesn’t estimate the value in the space. He doesn’t check to see that he the last digit is the first uncertain digit.

CONTRAST between the precision of an instrument and the precision of a measurement? What is the difference between these 2 concepts?

CONTRAST between (what is the difference) precision of an instrument and the precision of a measurement. Precision of the instrument depends on the value of the space between the unnumbered lines on an instrument’s scale. The precision of a measurement relies upon how close all measurements are to each other. (highest-lowest measurement)

STUDY these 6 questions for HW for Quiz 2a tomorrow.

CW 13 QUIZ 2a Assn How does a scientist record a measurement precisely? ( 2 ways) 2. How is the precision of an instrument calculated? 3.What is the relationship between the size of the scale divisions (gradations) and the precision of an instrument? 4.How is the measurement of a liquid recorded with precision and accuracy in a glass graduated cylinder? 5. How does error in precision of a measurement occur by a person making the measurements on an instrument? 6. CONTRAST between precision of an instrument and precision of a measurement?