Measurement Mini-Labs

 

Cohesion    - the molecular attraction by which the particles of a body are united throughout the mass

                   - the attraction between similar particles (i.e., water mlcl to water mlcl)

 

Adhesion    - the molecular attraction exerted between surfaces of bodies in contact

                   - the attraction between unlike materials (i.e., water mlcl to glass cylinder)

 

Meniscus     - the curved upper surface of a liquid column in small diameter container

                   - surface is concave when adhesion between liquid molecules and inner surface of

                     container is stronger than cohesion between molecules (convex when opposite is true)

 

Use of Graduated Cylinder:

          1.  All air bubbles must be removed (use stirring rod to remove them)

          2.  All droplets of liquid sticking to inner surface of cylinder above meniscus must be removed or

               absorbed before reading volume (tilt cylinder to allow liquid to absorb drops or use paper

               towel wrapped stirring rod to remove droplets).  Remember that clean glass/plastic ware

               should not allow droplets to stick to inside of container.  Should you be massing the graduated

               cylinder it must be dry on the outside as well.

          3.  Place cylinder on flat, level surface.  Read at eye level.

 

Finding Volume by Water Displacement Method:

          1.  Add water to about ½ of cylinder.  Remove bubbles and droplets.  Read to 1 decimal place.

            2.  Add object by tilting cylinder and gently allowing object to slide to bottom of cylinder.  If bubbles

               are observed on the object very gently shake the cylinder to dislodge them.  Read new (greater)

               volume and subtract the two volumes to obtain the volume of object. (1 decimal place)

 

Estimation:

            1.  The process of estimation of lengths and volumes is important in all science classes.  Add some

               water to the green detergent cup and estimate the amount of water you think might be there.

               Record this in mL.  Pour the water into a clean, dry graduated cylinder and read the value.  How

               close was your estimate?  Was all the water transferred to the graduated cylinder?

          2.  Repeat using another container to hold water.  Estimate the volume and then measure it.

 

Finding Mass Using Electronic Lab Scales:

          1.  Make certain the scales read zero grams.  Press Re-Zero (or TARE) if needed to zero the scales.

              When the numbers stabilize the scales are ready to be used.

          2.  If liquids are involved, place massing pan/paper on scales and Re-Zero.

          3.  Add object gently and allow scales to stabilize.  Read value and record on notecard.  Remove

               object and Re-Zero scales before leaving.  NEVER LEAVE ANYTHING ON SCALES FOR

                 MORE THAN  5  SECONDS.

 

Vernier Caliper Usage:

          1.  Open tension adjustment to allow sliding scale to move.

          2.  Using thumb wheel, open caliper enough to add item to measured.  Gently tighten caliper using

               thumb wheel and then gently tighten tension wheel.

          3.  Read scale using magnifying glass (as practiced in class identifying the correct vernier alignment.)

               I will be happy to confirm your reading.

          4.  Open tension wheel, open calipers with thumb wheel, remove object, then close calipers and

               gently close tension wheel.