Types of measurement Quantitative- use numbers to describe Qualitative- use description without numbers 4 feet extra large Hot 100ºF Scientists prefer QUANTITATIVE as there is no room for bias!

Remember… Numbers without units are meaningless. NO NAKED NUMBERS!!!

How good are measurements? Accuracy- how close the measurement is to the true value Precision- how well can the measurement be reproduced

Let’s use a golf anaolgy

Accurate?No Precise?Yes

Accurate?Yes Precise?Yes

Precise?No Accurate? No

Accurate?Yes Precise?We can’t say!

Significant figures (sig figs) How many numbers in a measurement means something When we measure something, we can (and do) always estimate between the smallest marks

Significant figures (sig figs) More marks = More precision Scientists always understand that the last number measured is actually an estimate 21345

Go to your lab station Note the smallest scale marks for each, and to what place you should estimate: 100 mL Grad Cyl 50 mL Grad Cyl 25 mL Grad Cyl 10 mL Grad Cyl 50 mL Buret 100 mL Buret Electronic balance 1mL so, est. → 0.1 mL 0.2 mL so, est. → 0.1 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 Rule Number Atlantic Pacific 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.

How many sig figs in these measurements? #1: 458 g 3 #2: 4850 g 3 #3: g 3 #4: g 9

Which measurement has 3 sig figs? A B C D. 830

Round the following numbers to three sig figs. #1: #2: #3:

Round to four sig figs. A B C D

What about this measurement? How many significant figures should you have? How do you write 30 with two sig figs?

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 = Tenths place (least precise Measurement) Also tenths place Find the answer first, then round to the least significant place of any measurement in the problem.

Practice #1: = 11.7 #2: = #3: = 6.2

– 2.00 = ? A B C D

Multiplication and Division Rule is different from addition and subtraction Answer has the same number of sig figs as the least significant number in the problem 3.6 x 653 = sig figs 3 sig figs Can ONLY have 2 sig figs = 2400 Remember, the rules are the same for division.

Multiplication and Division #1) 4.5 / = = 0.72 #2) 4.5 x = = 28 #3) / 1983 = =