Monday’s Meanderings… 1. Open House tonight – bring a parent & your Buff Binder… drop your lowest grade!!! 2. Calculators - $10 see me quick! 3. Check your grade on the back wall – see me if you were absent for test and binder check Friday. Zeros highlighted can still be fixed. Tutorials: Tu, Th, Fr this week 4. Put page 18 on your handout for today. 5. Get out page 9 to TURN IN!!!

Significant Figures

Nature of Measurement Part 1 – number Part 2 - scale (unit) – NO NAKED NUMBERS! Examples: 20 grams 20 grams 6.63 x Joule seconds Measurement - quantitative observation consisting of 2 parts consisting of 2 parts

Significant Figures All of the known digits + 1 estimated digit 7.21 cm

Uncertainty of Measurement The last digit on any physical measurement is always an approximation. Significant figures are the number of digits that can be accurately measured and the first uncertain digit.

Rule #1 All non-zero numbers are significant (numbers 1-9) 3.89 = __significant figures = ___ significant figures 3 4

Rule #2 Sandwich rule: all zero’s between non-zero or significant numbers are significant 202 = __ significant figures 3

Rule # = __ significant figures = __ significant figures 8 6

Rule #3 Leading zeros are NOT significant (zeros at the front of a 1-9 number)

Rule #3 Leading zeros are NEVER significant 0.91 = ___significant figures = __significant figures 2 2

Rule #4 Trailing (after) zeros are only significant if there is a decimal place in the number = __significant figures 5

1000. = ___ sig figs = ___ sig figs = ___ sig figs = ___ sig figs

Practice the zero rules: = __sig digs 9800 = __ sig digs = ___sig digs 6 4 2

Rule #5 Numbers obtained through counting or are defined have unlimited significant figures 60 minutes = 1 hour 24 people

Significant Figures in Calculations An answer cannot be more precise than the least precise measurement in the calculation

 1) nearest hundredth  2) nearest ones  3) nearest tens  4) nearest hundreds  5) nearest thousands

Rounding Look at the digit to the right of the one you need to round. If is is < 5 – leave it alone If it is  5 – round up m = _____ (4 sig figs) m

Rounding m = ___________ (2 sig figs) m 8792 m = _____________ (2 sig figs) 8800 m

To Do! Open up to page 17 On back in top margin do this: Round these numbers to 3 sig figs: 1) ) )

Multiplication and Division The answer should be rounded to the same number of significant figures as the least number of significant figures in the problem

Examples 4.56m x 1.4m = 5cm x 11cm = in x 19.35in = 6.4 m 2 60 cm in 2

Addition and Subtraction Answers should be rounded to the same place value as the least number of decimal places in the calculation

Examples m m = m = m m – m = m = m

Examples 34 cm cm = 79 cm 46.7 mL mL = mL = 99.0 mL

HUMP DAY!!! 9/17 On the bottom of pg. 17 (back) write a 3-5 sentence summary about sig figs. Make sure to answer the ESQ. Add your “A” to your star with Sharpie. Come get your calculator! Edit page 18 WITHOUT CHEATING!!!

Trade & Grade!!!

Accuracy and Precision p. 19 9/17 Obj: collect data and make measurements with accuracy and precision. ESQ: How is lab equipment used to measure precisely?

Accuracy Measurement of how close a measurement comes to the actual or true value

Precision Reproducibility of data Need more than one measurement

Accuracy and Precision Accurate and Precise x xx

Accuracy and Precision Not Accurate but they are precise x x x

Accuracy and Precision Accurate but Not Precise x xx

Accuracy and Precision Not Accurate and Not Precise x x x

Data Sets The data set is accurate if the values are close to the true value (literature value)

Data Sets The data set is precise if all of the values are close to each other.

Accurate or Precise? Several groups of students were testing different balances. They tested each balance several times using a 5.01 g weight.

Accurate or Precise? Balance Trial #1 Trial #2 Trial #3 Accurate?Precise? A B Mass (g) Yes No Yes

Accurate or Precise? Balance Trial #1 Trial #2 Trial #3 Accurate?Precise? C D Mass (g) No YesNo

Precision of Lab Equipment Precision refers to the reproducibility of data The more precise a piece of equipment, the more likely you are to get the same measurement repeatedly.

Precision of Lab Equipment The more precise piece of equipment has the smallest increment change between the markings

Precision of Lab Equipment Increment = 1 mL Increment = 0.2 mL More Precise

a) or More graduations – your measurements will be more precise

b) or More graduations – your measurements will be more precise

c) or More graduations – your measurements will be more precise

d) or More graduations – your measurements will be more precise

Measuring Precisely: markings = 1 mL precision = 0.1 mL 36.4 mL

Measuring Precisely: Markings = 0.1 cm Precision = 0.01 cm cm

On the back of p. 19 ColorName of equipment Marking increments PrecisionMeasurement Red Orange Yellow Green Blue Purple