Scientific Measurements

Chapter 3

Objectives

• Construct and use tables and graphs to interpret data sets.

• Solve simple algebraic expressions.• Measure with accuracy and precision (length,

volume, mass, temperature, time, etc.)• Convert within a unit (such as, centimeters to

meters).• Use common prefixes such as milli-, centi-, and

kilo-.• Use scientific notation, where appropriate.• Use ratio and proportion in the solution of

problems.

Objectives

•Determine the correct number of significant figures.•Determine percent error from experimental and accepted values.•Use appropriate metric/standard international (SI) units of measurement for mass (kg); length (m); and time (s).•Use Celsius and Kelvin scales.

Observations

• Qualitative: results in descriptions (Canadian geese)

• Quantitative: results in numerical form (15 Canadian geese)

Accuracy and Precision

• Accuracy: how close measurement is to true value

• Precision:

• how close several measurements are to the same value

• The number of digits in a measurement

Study Buddy Review

• How would you describe the following sets of numbers?

• 68.6, 68.7, 68.9 Goal = 23.0

• 40.02, 40.01, 39.99 Goal = 40.00

• 2.4, 6.0, 7.0 Goal = 4.0

• 0.874, 0.87, 0.86699 Goal= 0.87

Study Buddy Review

• How would you describe the following sets of numbers?

• 68.6, 68.7, 68.9 Goal = 23.0– Precise but inaccurate

• 40.02, 40.01, 39.99 Goal = 40.00– Precise and accurate

• 2.4, 6.0, 7.0 Goal = 4.0– Imprecise and inaccurate

• 0.874, 0.87, 0.86699 Goal= 0.87– Imprecise but accurate

Percent Error• Error: difference between experimental value and

accepted value• Accepted value: true or correct value from

literature• Experimental value: measured value determined

from lab

• % error = accepted value –experimental value x 100

accepted value

Study Buddy Review

• Convert the following to scientific notation:

0.005 g

10,000 m

• Convert the following to standard notation:

1.5 x 10-3 dL

2.2 x 105mL

Study Buddy Review

• Convert the following to scientific notation:

0.005 g 5 x 10-3 g

10,000 m 1 x 104 m

• Convert the following to standard notation:

1.5 x 10-3 dL 0.0015 dL

2.2 x 105mL 220,000 mL

The Metric System

Metric and SI units

• Metric System used in science

• SI System – International System of units based on metric system– Used to standardize quantities between

scientists

Common Units in Chemistry

Quantity it represents

SI unit Common metric unit in Chemistry

Length meter (m) centimeter (cm)

Mass kilogram (kg) gram (g)

Volume m3 (cubic meters)

milliliter (mL)

Temperature Kelvin (K) Celsius (oC)

Mass

• A measure of the quantity of matter; amount of material in an object

• Never changes

(Weight – force due to the pull of gravity on an object)

Volume

• Cube Demo• Cube is 10 cm x 10 cm x 10 cm = 1000 cm3

(also 1 dm x 1 dm x 1 dm or 1 dm3)

• Cube is filled by water in filled 1 liter beaker so1 L = 1000 cm3

1 L = 1000 mL= 1000 cm3 = 1 dm3

*IMPORTANT RELATIONSHIP: 1 cm3 = 1 mL

Temperature

• Temperature: a measure of the average kinetic energy of particles that make up substance

• Use Celsius or Kelvin temperature in chemistry• Kelvin Temperature scale based on absolute zero• Absolute zero or 0 K

– coldest possible temperature– Temperature where motion of particles stops

• A degree in Kelvin is equal in size to a Celsius degree

K = oC + 273

Metric Unit Prefixes

• Used to make the base units larger or smaller so that they are more convenient to use

Prefix Symbol Magnitude Multiple of base unit

Kilo k 103 1,000

Hecto h 102 100

Decka da 101 10

100 1

Deci d 10-1 0.1

Centi c 10-2 0.01

Milli m 10-3 0.001

Conversions to Know

1 Mm = 1 x 106 m

1 km = 1000 m

100 cm = 1 m

1000 mm = 1 m

1 x 106 μm = 1 m

• Can represent meters, grams, liters

Significant Figures

Uncertainty in Measurement• Measurements are uncertain

– Measuring instruments are never completely flawless

– Measuring always involves some estimation

Measuring Practice

Significant Digits/Figures

• All the certain digits in a measured quantity and 1 estimated digit of measurement.

• Rules for determining Significant figures: see handout

Study Buddy Review: Identify S.F.

1. 523.1 mL

2. 0.0025 mg

3. 5002 km

4. 1.8 x 10 6 lbs.

5. 0.090180 L

6. 2000 dogs

7. 2010. cats

8. 14,000.00 carrots

Study Buddy Review: Identify S.F.

1. 523.1 mL 4

2. 0.0025 mg 2

3. 5002 km 4

4. 1.8 x 10 6 lbs. 2

5. 0.090180 L 5

6. 2000 dogs 1

7. 2010. cats 4

8. 14,000.00 carrots 7