IS 220 Class 3
Measurement
Review last week's experiments with "salty chalk soda" - solicit explanations of "mysteries" (e.g. salts disappear, then reappear). Let's do some measurements for another experiment, and observe (AND RECORD!) very closely how we do them.
Instructor goes through measurement procedures listed below, in front of class, with digital camera connected to TV to help with close-ups of e.g. readings on scales and cylinders). Instructor keeps record of observations on blackboard, stressing how they should also keep written record; photo of papers, put on TV, and eventually onto Web page.
Materials
- paper & pencils - don't even proceed unless all students have paper with proper header information
- 1 cup per group, with a little mre than 50 ml of water
- scales (triple beam balances)
- graduated cylinders
- various salts: NaCl, NaHCO3, MgSO4
- water
- camera, TV
Procedure
- demo by instructor of liquid measurement:
- put cylinder's marking for desired amount at eye-level, draw perspective views showing why
- pour in SLOWLY - harder if you overshoot and have to pour some out and retry!
- each group measures out 50 ml of water - each student gets to try it, instrictor checks on their accuracy, makes suggestions
- each student will carefully weigh out 2.0 g NaHCO3, and compare results with other students in group
- adjust scale to read zero when no load
- put piece of paper on scale, and note its weight - write it down!
- add 2.0 g to weigt of paper (do arithmetic on lab sheet!), then adjust scale slide to mark new weight obtained by this addition
- add NaHCO3 onto paper on scale til rebalanced
- each person in group will reweigh the salt sample, and record the value on own data sheet
- instructor checks each person's weighing (compare their written result with actual amount)
- break in "vow of silence" for inter-group comparisons
- wrap up measured salt for use next time, CAREFULLY LABELLED with group name, "2.0 g baking soda"
Leave time for cleanup!!