Honors ChemistryUnit 1: Introduction to Chemistry

Science Measurement and MathSignificant Figures, SI Units, and Scientific Notation

Honors ChemistryUnit 1: Introduction to Chemistry

Learning Objectives:

I can use task appropriate instruments to obtain accurate measurements.

I can use the language of science to represent values in a clear and accurate manner.

BeakerSoln prep, storage, rxns

250 mL (+/- 10 mL )

Graduated CylinderVolume transfer

250 mL (+/- 1 mL )

Volumetric FlaskPrecise final vol for dilutions

250 mL (+/- 0.08 mL )

Consider 3 types of glassware for liquids:

LO: I can use task appropriate instruments to obtain accurate measurements.

LO: I can use task appropriate instruments to obtain accurate measurements.

Accuracy vs. Precision

Accurate: WHY?!

Precise: WHY?!

Accurate and precise: WHY?!

Confidence in Measurements

Accuracy: How close a number is to the actual value

Precision: How close the measurements are to each other; reproducible

% Error = l Experimental – Theoretical ITheoretical Value

X 100

LO: I can use task appropriate instruments to obtain accurate measurements.

How do you determine the correct number of digits to record from a measurement?

Include: All readable digits…CertainPlus 1 estimated digits…Uncertain

An estimated digit should be included in ALL measurements taken in lab.

Number of digits in a measurement tells how CONFIDENT you are in that measurement.

LO: I can use task appropriate instruments to obtain accurate measurements.

Include all digits with certainty plus one with uncertainty

Triple Beam Balance Mass = 2 7. 7 0 g

One digit of uncertainty

LO: I can use task appropriate instruments to obtain accurate measurements.

Tell your neighbor what you think the length of this piece of paper is. To what place should you report the value?

11.63 cm

LO: I can use task appropriate instruments to obtain accurate measurements.

1)To what place should the volume be reported?

2) What is the volume of liquid in the graduated cylinder?

hundredths

Volume = 21.62 mL

22

LO: I can use task appropriate instruments to obtain accurate measurements.

LO: I can use the language of science to represent values in a clear and accurate manner.

What confidence should you have in values that you didn’t measure?

Value Sig Figs

0.0005 12.07 3400 11.0 2

9000. 40.0000703 3

Can you figure out the rules?

Significant Figures!!

Significant Figures The Rules

1. Non-zero #’s are ALWAYS significant

2. Zeros between two non-zeros are significant

3. Decimal present: -Trailing zeros are significant (ex. 27.00 4 sig figs) -Zeros in front of the non-zeros are NOT significant (ex. 0.00345 3 sig figs)

4. Decimal absent:-Trailing zeros are NOT significant (ex. 8900 2 sig figs)

LO: I can use the language of science to represent values in a clear and accurate manner.

Calculations w/ Significant Figures The Rules

Multiplication/Division

Limited by the value with the fewest sig figs

23.4 x 1.9 = 44.46

Addition/Subtraction

Determined by the largest digit of

uncertainty

35.78+ 67.9

103.68

= 44

2 sig figs X

= 103.6

4 sig figs

LO: I can use the language of science to represent values in a clear and accurate manner.

LO: I can use the language of science to represent values in a clear and accurate manner.

Scientists use the SI (Système international) of measurement

-To improve communication-Convenience -Diminish likelihood of errors

Curious about how and why standardized units came to be? Learn more here: The Bitter Class Struggle Behind Our Definition of the Kilogram

https://www.theatlantic.com/science/archive/2018/10/standard-units-kilogram-tyranny/574276/

SI Base Unit used in Chemistry:Quantity Unit Abb. Measurement

ToolLength Meter m Ruler,

meterstickMass Kilogram* kg Balance

Time Second s Stopwatch

Temperature Kelvin* K ThermometerAmount of Substance

Mole* mol NA

Current Ampere* A Ammeter

Luminous Intensity

Candela cd Photometer

LO: I can use the language of science to represent values in a clear and accurate manner.

*How we define these base units will change on World Metrology Day, May 20, 2019. Learn more here.

https://www.nature.com/news/new-definitions-of-scientific-units-are-on-the-horizon-1.22837

All measurements have what two things?

LO: I can use the language of science to represent values in a clear and accurate manner.

Fundamental Units vs. Derived Units

Number and Unit

Function of fundamental

units

Base Units defined wrt natural

phenomenon

LO: I can use the language of science to represent values in a clear and accurate manner.

Quantity Symbol Unit

Area A m2

Volume V m3

Velocity v m/s

Acceleration a m/s2

Wavenumber σ m-1

Density ρ kg/m3

Concentration c mol/m3

SI Derived Units expressed in terms of Base Units

LO: I can use the language of science to represent values in a clear and accurate manner.

LO: I can use the language of science to represent values in a clear and accurate manner.

Scientific Notation

Coefficient between1 and 10

5478.8 = 5.4788 x 10 3

base

exponent

Standard Notation Scientific Notation

93456.78

0.003467

8.327 x 107

67.00942

6.48 x 10-6

3.467 x 10-39.345678 x 104

6.700942 x 10183270000

0.00000648

123

LO: I can use the language of science to represent values in a clear and accurate manner. Metric Prefixes Scientific Notation

Prefix Sym Multiplier Exp Norm E Giga G 1,000,000,000 109 1 x 109 1E9

Mega M 1,000,000 106 1 x 106 1E6

Kilo k 1000 103 1 x 103 1E3

Hecto h 100 102 1 x 102 1E2

Deka da 10 101 1 x 101 1E1

Base Unit (gram, meter, liter, etc.) 100 1 x 100 1E0

Deci d 0.10 10-1 1 x 10-1 1E-1

Centi c 0.01 10-2 1 x 10-2 1E-2

Milli m 0.001 10-3 1 x 10-3 1E-3

Micro m 0.000001 10-6 1 x 10-6 1E-6

Nano n 0.000000001 10-9 1 x 10-9 1E-9

Pico p 0.000000000001 10-12 1 x 10-12 1E-12

Me

mo

rize

!!!

LO: I can use the language of science to represent values in a clear and accurate manner.

1. How many picoliters are in 1 liter?

2. How many grams are in 1 megagram?

3. How many meters are in 1 dekameter?

4. How many deciseconds are in 1 second?

1 L = 1 x 10-12 pL

1 x 102 m = 1 dam

1 x 106 g = 1 Mg

1 x 101 ds = 1 s

Human hair ~10-50 µm

LO: I can use the language of science to represent values in a clear and accurate manner.

What is the width of a human hair in meters?

Dimensional Analysis

1. Start with what is given2. Convert to the base unit desired unit

10 µm= ? mX

1 m

106 µm

= 10-5 m

1

LO: I can use the language of science to represent values in a clear and accurate manner.

1. Convert 4.5 ng to mg.

2. Convert 1.5 dm to hm.

Try these:

X4.5 ng

X1g

109 ng

103 mg

1 g 1

4.5 x 10-6 mg=

X1.5 dm

1X

1 m

101 dm

1 hm

102 m 1

1.5 x 10-3 hm=

1

LO: I can use the language of science to represent values in a clear and accurate manner.

Convert 8.3 m/s to nm/ms

How about this one?

Some tips:1. Identify the conversions 2. Work one at a time3. Always check by cancelling units

X8.3 m

sX

109 nm

1 m

1 s

103 ms ms

8.3 x 106 nm=

m nm, s ms

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