Lab Exercise 1        Glass Working, Weighing, and Significant Figures

 

Recording of Data and Observations

 

One of the several purposes of the laboratory part of this course is to learn to correctly record laboratory data and observations.  The laboratory notebook of a practicing scientist becomes legal record and has to be kept in a manner that guarantees that it is accurate and not altered at a later date.  You should begin to learn in the laboratory how to correctly collect and record relevant data and observations that is the reason for the following rules.

 

Procedures

  1. All data and observations are to be recorded directly onto the laboratory report sheet in blue or black non-erasable ink.
  2. Once the data has been recorded, there are to be no strikeovers or scratch-outs or whiteout.  Put one line through the data so that it can still be read and then write the new observation above it or in an appropriate place so that it can be easily read.
  3. The data section of your laboratory report sheet and all changes in data are to be signed or initialed by your instructor before you leave the laboratory at the close of the period.  No changes are to be made after this.

 

These procedures are explained below.  Number (1) should be fairly clear by itself, but note what is intended.  Always write data and observations directly onto your report sheet in the designated place.  Do not use scrap pieces of paper, the palm of your hand or some place on your report sheet not prepared for data or observations.  Data found written on scrap pieces of paper, etc., may be confiscated and destroyed by your instructor.  This means, for example, that you have to take your report sheet with you when you go to the balance so that you can record the mass directly onto your sheet.  It also means to use reasonable care when recording an observation.  The recording is to be made with permanent blue or black ink so that it cannot be erased or changed. The excuse that you forgot your pen, or do not have one, is not acceptable.  It is a very good idea to put one or two ballpoint pens in your laboratory locker and leave them there between lab periods so that you will always be properly equipped.

 

Sometimes you may decide that a particular observation is in error.  Number (2) is the procedure to deal with this problem.  As illustrated in Figure 1.1 on the next page, draw a line through the discarded observation and write in the new one.  Note that the original can still be read.  A ÒstrikeoverÓ is where you write the new value on the top of the original value.   Thus the original cannot be read.  As also illustrated, ÒstrikeoversÓ or whiteout are prohibited.  Any method of altering the original recording, except with a single line out is not acceptable.  In case you need more space to take down data or observation, use an appropriate blank part of your report sheet on which you have put the necessary labels, etc., to make it clear.

 

            FIGURE 1.1 Data Correction

                    

                         correct                                                                 wrong

            

            12.971  ! new value                                       12.971

         12.791  ! original value                no strikeovers           12.771 ! no obliterations   

                                                                                                                     no whiteout

 

Number (3) is self-explanatory; however, you should remember that changing data to get ÒbetterÓ answers is cheating.

 

Other parts of your laboratory report DO NOT have to be in ink.  The calculations that are made from the data may be done on another sheet of paper first, if you prefer, and then transferred to the report sheet.  They may be done in pencil and may be erased and changed in necessary.  The same applies to the problems and application of principle sections at the end of the report sheet.  Be sure, however, that you always show a complete set-up with correct units and the proper use of significant figures. 

 

Glassware, Practice Weighing, and Significant Figures

Glassware Fabrication

 

The following lists and illustrates the several pieces of glassware that you are going to make for this course.  Your instructor will demonstrate the basic operations needed for working glass tubing and rod.

 

Caution:  When you take glass from the glass bin, be sure to check its diameter because the wrong sizes sometimes get put into the various bins.  Please recall that safety rule that all glass tubing and rod is to be fire polished before it is used!

 

Stirring Rods

Make a total of four from the rods that are available.  The stir rods should be approximately 18 cm long.  (Be sure to use solid rod and not tubing!)

 

            FIGURE 1.2    Stirring Rods

 

 

 

Straight Tubes

Make two straight tubes of 6 mm tubing: one 6 cm long, and one 18 cm in length as shown in FIGURE 1.3.

 

            FIGURE 1.3    Straight Tubes

 

 

90¡ Bends

Make two 90¡ bends as diagramed in FIGURE 1.4

 

            FIGURE 1.4    Bends

 

 

Eye Dropper (Medicine Dropper)

Make one pair of eye droppers that are approximately 10 cm in length.

 

            FIGURE 1.5    Eye Droppers

 

 

 

 

 

 

Glass Working

Have your instructor check and initial your stir rods, 90¡ bend, straight tubes, and eye droppers.

 

Stir Rod Ends Smooth                        _____              Straight Tubes Smooth           _____

 

90¡ Bend                                 _____              90¡ Bend Ends Smooth           _____

 

Eye Dropper                           _____

 

 

Introduction to the Use of the Balances

 

You instructor will show you how to correctly operate both the milligram top loading balance and the quad-beam balance.  Weigh your assigned object(s) on both types of balances and record your values below.

 

TABLE 1.1     First Trial      (Metal Slug)

 

Object Description                 ________________________________________________

 

Object Number                       ________________________

 

Quad-Beam Balance                ________________________

 

Electronic Top-Loader            ________________________

 

 

TABLE 1.2     Second Trial

 

Object Description                 ________________________________________________

 

Quad-Beam Balance                mass sample and paper           ________________________

                                               

                                    mass paper                              ________________________

                                               

                                                mass sample                            ________________________

 

 

Electronic Top-Loader            mass sample and paper           ________________________

                                               

                                                mass paper                              ________________________

                                               

                                                mass sample                            ________________________