Post on 28-Dec-2015
Types of measurementQuantitative- use numbers to describe
Qualitative- use description without numbers
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Scientists prefer QUANTITATIVE as there is no room for bias!
How good are measurements?Accuracy- how close the measurement is to the true value
Precision- how well can the measurement be reproduced
Significant figures (sig figs)How many numbers in a measurement
means somethingWhen we measure something, we can
(and do) always estimate between the smallest marks.
21 3 4 5
Significant figures (sig figs)More marks = More precision
Scientists always understand that the last
number measured is actually an estimate
21 3 4 5
Go to your lab stationNote the smallest scale marks for each, and to what place you should estimate:100 mL Grad Cyl50 mL Grad Cyl25 mL Grad Cyl10 mL Grad Cyl50 mL Buret100 mL BuretElectronic balance
1mL so, est.→ 0.1 mL
1mL so, est.→ 0.1 mL
0.2 mL so, est.→ 0.1 mL
0.1mL so, est.→ 0.01 mL
0.1mL so, est.→ 0.01 mL
0.2 mL so, est.→ 0.1 mL
0.01 g
Sig Figs (sig digs)Since science tools aren’t precise to infinite digits,
we say only certain numbers are
“significant” to us.
Atlantic/Pacific RuleNumber AtlanticPacific
• If decimal is “Present” start counting from the Pacific Side at the first “non-zero” digit and continue counting until the number ends.
• If the decimal is “Absent” start counting from the Atlantic side at the first “non-zero” digit and continue counting until the number ends.
What about this measurement?
How many significant figures should you have?
How do you write 30 with two sig figs?
30.
2010 30 40 50
Adding and Subtracting with sig figs
Your answer when you add or subtract can not be more “significant” than your worst estimate.
Find the answer, then round to the least significant place of any measurement in the problem
For example
27.93 6.4+ = 34.33
Tenths place(least preciseMeasurement)
Also tenths place
Find the answer first, then round to the least significant place of any measurement in the problem.
Multiplication and DivisionRule is different from addition and
subtractionAnswer has the same number of sig figs
as the least significant number in the problem
3.6 x 653 = 2350.82 sig figs 3 sig figs Can ONLY have 2 sig figs
= 2400
Remember, the rules are the same for division.