Measurements with Range Uncertainty CHEMISTRY 11 UNIT 1.3

250 mL Erlenmeyer Flask - LIQUID Read volume from eye level, bottom of meniscus Class values (mL): 112.5, 150, 151, 153, 154, 155, 157, 158, 160, 162, 175

50 mL Erlenmeyer flask - LIQUID Read volume from eye level, bottom of meniscus Class values (mL): 15, 17, 25, 27, 28, 29, 30, 31

400 mL beaker - LIQUID Read volume from eye level, bottom of meniscus Class values (mL): 115, 120, 155, 170, 172, 175, 178, 182, 185

50 mL beaker - LIQUID Read volume from eye level, bottom of meniscus Class values (mL): 15, 16, 17, 18, 27

100 mL graduated cylinder - LIQUID Read volume from eye level, bottom of meniscus Class values (mL): 73, 77, 78, 79, 88

10 mL graduated cylinder - LIQUID Read volume from eye level, bottom of meniscus Class values (mL): 3.4, 3.5, 3.6, 3.7, 3.9

Electronic balance – 10 DIMES Zero/Tare scale before beginning. Read all digits. Class values (g): 1.75, 17.5, 17.6, 17.7

Triple -beam balance – 10 DIMES Quadruple Adjust largest mass (100 g increments) first until the right side drops. Move back one increment. Adjust next largest mass (10 g increments) and so one until right side is balanced in line with marker on right side. Record the value starting with hundreds, then tens, then ones.... Class values (g): 7, 7.7, 17.53, 17.57, 17.6, 17.7, 17.8

Centimetre ruler – POST-IT NOTE Make sure ruler is parallel to object being measured. Record measurement. Class values (cm): 4.6, 7, 7.1, 7.2, 7.3, 7.4, 7.5, 10

Centimetre ruler with millimetre divisions – POST-IT NOTE Make sure ruler is parallel to object being measured. Record measurement. Class values (cm): 3.5, 7, 7.2, 7.3, 7.4

Recording Measurements  Record all CERTAIN digits from marked lines plus one UNCERTAIN digit (an estimate)  Write down your RANGE UNCERTAINTY of +/- one-tenth to one-half of the smallest marked division  Okay, let’s try those measurements again!

250 mL Erlenmeyer Flask - LIQUID  153 mL +/- 3 mL

50 mL Erlenmeyer flask - LIQUID  25 mL +/- 3 mL

400 mL beaker - LIQUID  174 mL +/- 5 mL

50 mL beaker - LIQUID  13 mL +/- 2 mL

100 mL graduated cylinder - LIQUID  77.2 mL +/- 0.2 mL

10 mL graduated cylinder - LIQUID  3.42 mL +/ mL

Electronic balance – 10 DIMES  17.6 g +/- 0.1 g

Triple -beam balance – 10 DIMES Quadruple  g +/ g

Centimetre ruler – POST-IT NOTE  7.4 cm +/- 0.1 cm

Centimetre ruler with millimetre divisions – POST-IT NOTE  7.35 cm +/ cm

Significant Figures (a.k.a. Significant Digits)  You must be able to read a measuring device correctly because of SIGNIFICANT FIGURES: some digits are important because they are likely to be true, we call these SIGNIFICANT FIGURES or SIG FIGS for short  Every measuring device has a maximum number of Sig Figs.  You cannot use a school centimetre ruler and say that a Post-it Note is cm wide.

Sig Fig examples   2 sig figs   5 sig figs   2 sig figs  405  3 sig figs

Sig Figs continued  Any number that is COUNTED DIRECTLY and NOT MEASURED OR ESTIMATED should not be considered as having Sig Figs.  Example:  There are 30 students in Ms. Dhir’s Chemistry 11 class.  “30” is an exact number, no part of this is an estimate and we do not have any RANGE UNCERTAINTY with it.