1.3.3 CIA Demonstration: Precision and Accuracy with Glassware

Question 1

CIA Demonstration: Precision and Accuracy with Glassware

Answer 1

• There are many types of glassware for measuring volume in the laboratory.
• Precision is the ability to reproduce a measurement, while accuracy is how close the measurement is to the true answer.
• A pipet is more precise because of its small cross-section at the meniscus.

Question 2

volumetric pipets and graduated cylinders

Answer 2

• There are many types of glassware for measuring volume in the laboratory.
• Volumetric pipets and graduated cylinders are two
  examples of laboratory glassware.
• Volumetric pipets are used to deliver specific fixed volumes of liquids. For example, some volumetric pipets are calibrated to deliver 50.00 mL of liquid, while others are calibrated to deliver 5.00 mL of liquid.
• Graduated cylinders are used to measure variable volumes of liquid. For example, a 50 mL graduated cylinder could be used to deliver any volume between 0.0 mL and 50.0 mL, such as 38.3 mL.

Question 3

precision

Answer 3

• Precision is the ability to reproduce a measurement, while accuracy is how close the measurement is to the true answer. For example, If the goal is to hit the bull’s eye, the three throws on the left are precise, but not accurate. The throw on the right is accurate.
• Different pieces of glassware have different degrees of precision and accuracy associated with them.

Question 4

volume

Answer 4

• The volume of water delivered by a piece of glassware can be calculated from the mass of water delivered and the density of water at a specific temperature.
• The average volume of water delivered is 49.87 mL for both pieces of glassware. Therefore, the two pieces of glassware are equally accurate.
• However, the standard deviation of the volume delivered by the volumetric pipet is smaller. Therefore, the volumetric pipet is more precise than the graduated cylinder. A pipet is more precise because of its small cross-section at the meniscus.