Experiment 1 - Measurement

Introduction

Volume Measurements - Graduated Cylinder

In any volume measurement we need to approach the measuring instrument at proper eye position, at eye level. When we are up close to the liquid level at eye level, we will observe that the surface of the liquid forms a "lens-shaped". This is called the meniscus. In taking the measurement, we always read the bottom of the meniscus. Below is an example of a reading taken of a liquid in a graduated cylinder. The diagram shows an expanded view of the portion of the cylinder near the surface of the liquid.

Let's analyze this measurement:

  1. Upon inspection of the graduated cylinder, we observe that the finest division is a 1 mL division.
  2. We can always make an estimate of a reading to within the finest division. Therefore, to the best of my judgement, I conclude that this particular graduated cylinder is able to provide a reading accuracy to +/- 0.2 mL. (Note: A plus or minus 0.2 mL reading accuracy means that a volume measurement using this graduated cylinder will contain uncertainty in the first decimal place.)
  3. The bottom of the meniscus lines up with the 4th finest division above the 10 mL mark.
  4. The volume reading is determined to be 14.0 mL. This volume reading has 3 significant figures. (Note: the '0' in this measurement is an uncertain figure. This measurement is accurate to 14.0 +/- 0.2 mL. It means that using this graduated cylinder, the accuracy of the volume of the liquid is between 13.8 mL to 14.2 mL.)

 

 


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