Chapter 2 – Measurements & Calculations

Table of Contents

Section Title1 Scientific Method

2 Units of Measure

3 Using Scientific Measurements

Objectives (Section 1)

Describe the purpose of the scientific method.

Distinguish between qualitative and quantitative observations.

Describe the differences between hypotheses, theories, and models.

The Scientific Method

Science progresses through carefully planned investigation

Scientific Method is a logical approach to solving problems by observing and collecting data, formulating hypotheses, testing hypotheses, and formulating theories that are supported by data.

Which chemical is the best penny cleaner?

Which is a better penny cleaner?

1. Ketchup

2. Vinegar

3. Salt

Observing & Collecting Data

• Observing is the use of the senses to obtain information.

• data may be • qualitative (descriptive)• quantitative (numerical)

• A system is a specific portion of matter in a given region of space that has been selected for study during an experiment or observation.

Qualitative vs. Quantitative Data

Which is a better penny cleaner?

What is the length of this pen?

Which is more subjective? Why?

Which is considered more desirable for science? Why?

Formulating Hypotheses

• Scientists make generalizations based on the data.

• Scientists use generalizations about the data to formulate a hypothesis, or testable statement.

Hypotheses are often “if-then” statements.

Testing Hypotheses

• Testing a hypothesis requires experimentation that provides data to support or refute a hypothesis or theory.

• Controls - experimental conditions that stay constant

• Variables - experimental conditions that change

Theorizing

• A model in science is more than a physical object; it is often an explanation of how phenomena occur and how data or events are related.• visual, verbal, or mathematical• example: atomic model of matter

• A theory is a broad generalization that explains a body of facts or phenomena. example: atomic theory

Scientific Method (Visually)

Algebra Review

Scientific Notation Pages

Converting to Scientific Notation Move decimal to have one digit (non-zero) to the LEFT

Example: 234 = 2.34 x 102

Example 2: 0.52 = 5.2 x 10-1

Decimal to the RIGHT = Negative exponent

Decimal to the LEFT = Positive exponent

Complete pp. 2 #1-5

Scientific Notation Pages (2)

Converting from Scientific Notation Move decimal to a regular value

Example: 4.92 x 102 = 492

Example 2: 5.2 x 10-4 = 0.00052

Positive exponent = MOVE decimal to the RIGHT

Negative exponent = MOVE decimal to the LEFTNegative exponents = SMALLER than 1

Complete pp. 2 #1-5

Exponent Operations

Use the calculator!!

Don’t forget the parentheses

Complete pp. 3 #1, 3, 5, & 7

Significant Figures & Operations

Use the rules on page 4 + pp. 47 !!

For add/subtract OR multiply/divide, use the rules on page 5 + pp. 49 !!

Significant Figures

Significant Figs & Operations

Section 2.2 – Units of Measurement

Lesson Starter

Would you be breaking the speed limit in a 40 mi/hr zone if you were traveling at 60 km/hr?

one kilometer = 0.62 miles

Lesson Starter

Would you be breaking the speed limit in a 40 mi/hr zone if you were traveling at 60 km/hr?

one kilometer = 0.62 miles

60 km/h = 37.2 mi/h

You would not be speeding!

km/h and mi/h measure the same quantity using different units

Objectives 2.2

Distinguish between a quantity, a unit, and a measurement standard.

Name and use SI units for length, mass, time, volume, and density.

Distinguish between mass and weight.

Perform density calculations.

Transform a statement of equality into conversion factor.

Measurement vs. Quantity

Measurements represent quantities.

A quantity is something that has magnitude, size, or amount.

measurement quantity the teaspoon is a unit of measurement volume is a quantity Measurement = number + unit

The choice of unit depends on the quantity being measured.

SI Measurement

Scientists all over the world have agreed on a single measurement system called Le Système International d’Unités, abbreviated SI.

SI has 7 base units Everything else is DERIVED from these 7 units Hence, called Derived SI unit

SI Base Units

7 Base Units

L-MM-TT (Length, Mass, Mole, Time, Temp)

Current (A)

Luminous Intensity (cd)

Prefix Symbol 10n Common

Kilo k 103 Thousand

hecto h 102 Hundred

deca da 101 Ten

100 One or Unit

deci d 10-1 Tenths

centi c 10-2 Hundredth

milli m 10-3 Thousandth

SI Prefixes – Need to Know

SI Prefixes - Extended

Converting SI Units

Kilo hecto deca U deci centi milli

Complete pages 6 & 7

Mass vs. Weight

Mass is a measure of the quantity of matter.Kilogram (kg)

Weight is a measure of the gravitational pull on matter.Newtons (Don’t need to know units now)

Mass does not depend on gravity.

Length Matters

Length is a measure of distance.Meter (m)

Kilometer (km) – longer distances

Centimeter (cm) – shorter distances

Derived SI Units

Combine more than one SI unit into a new unit

Called derived SI units since they are derived from the 7 SI units

Volume

Volume is the amount of space occupied by an object.

Cubic meters (m3) Cubic centimeter (cm3) is often used Liter (L) is a non-SI unit 1 L = 1000 cm3

1 mL = 1 cm3

Density

Density is the ratio of mass to volume, or mass divided by volume.

kg / m3

Can also use: g/mL = g/cm3

density =

mass

volume or D =

m

V

Conversion Factor

Conversion factor is a ratio derived from the equality between two different units that can be used to convert from one unit to the other.

Accuracy & Precision

Accuracy refers to the closeness of measurements to the correct or accepted value of the quantity measured.

Precision refers to the closeness of a set of measurements of the same quantity made in the same way.

Accuracy & Precision

Percentage Error

Percentage error is calculated by subtracting the accepted value from the experimental value, dividing the difference by the accepted value, and then multiplying by 100.

Percentage error = Value

experimental-Value

accepted

Valueaccepted

× 100

Percentage Error Problems

A student measures the mass and volume of a substance and calculates its density as 1.40 g/mL. The correct, or accepted, value of the density is 1.30 g/mL. What is the percentage error of the student’s measurement?

What is the percentage error for a mass measurement of 17.7g, given the correct value is 21.2g?

Percentage Error Problems

€

1.4 −1.3

1.3×100 = 7.7%

€

17.7 −21.2

21.2×100 = 17%

Section Review & HW

Complete Section Review pp. 42 & pp. 57

Complete Practice Problems pp. 59 (#16 – 23)