IMAGE. 25-mL graduated cylinder.
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Step 1: Determine the scale increment:
To find the scale increment, subtract the values of any two
adjacent labeled graduations and divide by the number of intervals
between them.
What is the scale increment for the 25-mL graduated cylinder? Answer
In the 25-mL graduated cylinder, first subtract 25 mL - 20 mL = 5 mL. Next, count that ten intervals are between the labeled graduations. Therefore, the scale increment is 5 mL/10 graduations = 0.5 mL/graduation. Step 2: Use the graduations to find all certain digits:
Use the labeled graduations and the scale increment to find the certain digits in the measurement.
What are all of the certain digits for the 25-mL graduated cylinder? Answer
The volume is greater than 20 mL, since the last labeled graduation below the meniscus is 20. Next, use the scale increment. There are graduation marks
below the meniscus, and each graduation represents 0.5 mL, so the certain digits of the reading are 21 mL. Step 3: Estimate the uncertain digit and obtain a reading:
Estimate the distance that the meniscus lies between the two graduations as a decimal fraction and multiply by the scale increment.
What is the volume you should record? Answer
The bottom of the meniscus is about nine tenths of the way between the two graduation marks. Thus, the uncertain digit is calculated as (0.9 increment) * (0.5 mL/increment) = 0.45 mL = 0.4 mL. And, the volume to be recorded is 21.4 mL. |
