• most scientific advances result from carefully planned investigation.

Scientific Method

• a logical approach to solving problems.

Observing• collecting data

• measuring

Formulating Hypotheses• analyzing data

• predicting

Testing• experimenting• collecting data

If data doesnot supporthypothesis

Theorizing• constructing models

• predicting

Publish Results• communicating

1. Observing

• Making measurements and/or collecting data.

• Data can be either qualitative (descriptive/words) or quantitative (numerical).

2. Formulating Hypotheses

• A testable statement that serves as the basis for making predictions.

3. Testing Hypotheses

• Experiments are performed that provide data to support or refute a hypothesis.

4. Theorizing

• When predictions of the hypothesis are successful, scientists use models (explanations of how phenomena occur and how events are related).

• Theories: a generalization that explains body of facts and phenomena.

Units of Measurement

• a measurement represents a quantity that has magnitude, size or amount.

• scientists use SI units to describe measurements.

• there are seven base SI units.

Common SI Prefixes

• prefixes are used to represent quantities that are larger or smaller than the base unit.

Density

• the ratio of the mass to volume

What is the density of a sample of ore that has a mass of 74.0 g and occupies 20.3 cm3?

Answer: 3.65 g/cm3

Find the volume of a sample of wood that has a mass of 95.1 g and a density of 0.857 g/cm3.

Answer: 111 cm3

Diamond has a density of 3.26 g/cm3. What is the mass of a diamond that has a volume of 0.35cm3?

Answer: 1.14 g

Using Scientific Measurements

• accuracy: the closeness of

measurements to the correct or

accepted value.

• precision: closeness of a set of

measurements of the same

quantity made in the same way.

Percent Error

• a calculation used to see how accurate your measurements are.

Error in Measurement

• some error or uncertainty always exists in any measurement.

due to:

1. Skill of the measurer.

2. Precision of the measuring instruments.

Conversion Factors

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

Ex: Convert 0.014 mg to grams.

0.014 mg X (1 g / 1000mg) = 0.000014 g

Ex: Convert 6.2 km to m.

6.2 km X (1000m/1km) = 6200 m

Ex: How many cg are there in 6.25 kg?

6.25 kg X (1000g/1kg) X (100cg/1g) =

625000 cg

Conversion Practice!

Mark McGuire hit 70 homeruns in the 1998 season. Given thatthere are 4 bases with 90 feet between each base, how many miles did he run last season from homeruns? (5,280 feet per mile).

According to current records, Kamato Hongo of Japan lived to the ripe old age of 116 yrs old! How old is this women in seconds?

Do Now!!!!!!!!!!!!!!!!!!!!!!!!!!!

Significant Figures

“Atlantic-Pacific Rule”

1. “P” is for Pacific: meaning the decimal point is PRESENT.

• Count significant figures starting with the first non-zero digit on the left.

Ex: 0.004703

18.00

0.0205

2. “A” is for Atlantic: meaning the decimal point is ABSENT.

• Count significant figures starting with the first non-zero digit on the right.

Ex: 140,000

20060

1,000,000

4 significant figures

4 significant figures

3 significant figures

2 significant figures

4 significant figures

1 significant figures

Rules for Rounding

1. If the number being examined is less than 5, drop it and all the figures to the right of it.

2. If the number being examined is more than 5, increase the number to be rounded by 1.

3. If the number being examined is 5, round the number so that it will be even.

Ex: Round 62.5347 to four significant figures.

Answer: 62.53

Round 3.78721 to three significant figures.

Answer: 3.79

Round 726.835 to five significant figures.

Answer: 726.84

Round 24.8514 to three significant figures.

Answer: 24.8 (since the “8” is even it stays as “8”)

Scientific Notation

• used to express very large and very small numbers.

• follows the format:

M x 10n where 1≤M<10

n is any integer.

Using Significant Figures in Calculations

1. Addition and Subtraction

• Your answer must have the same number of decimals as the value with the fewest number of decimals.

Ex: 25.1g + 2.03g = ?

Answer: 27.1 g

Ex: 5.44m – 2.6103m = ?

Answer: 2.83m

Ex: 87.3cm – 1.655cm = ?

Answer: 85.6cm

2. Multiplication and Division

• Your answer can have no more significant figures than are in the measurement with the fewest number of significant figures.

Ex: 3.05g / 8.47mL = ?

Answer: 0.360 g/mL

Ex: 51.4g / .71cm3 = ?

Answer: 72 g/cm3

Ex: 21.100cm x 0.500cm x 2.90cm = ?

Answer: 30.6 cm3

Chapter 3 Exam will Cover:

Scientific Method Units of Measurement Density Conversion Factors Accuracy and Precision (10% error = good accuracy!) Significant Figures Calculating Percent Error Rounding