Chapter 2
Scientific Method
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Section 2-1 Click to return to Chemistry Page
Objectives
- Describe the purpose of the scientific method
- Distinguish between qualitative and quantitative observations.
- Describe the differences between hypotheses, theories, and models.
- Observing and Collecting Data
- observing- the use of the senses
- Qualitative measurement- describes the quality of a substance.
- Quantitative measurement- describes the substance using a numerical value.
- System- a specific portions of matter in a given region of space.
- Formulating Hypotheses- testable statement
- Testing Hypotheses-Requires experimentation
Stages in the Scientific Method ( pg 31)
- Theorizing-a broad generalization
Units of measurement
Sections 2-2
Objectives
- Distinguish between a quantity, a unit and a measurement standard.
- Name the SI units for length, mass, time, volume, and density.
- Distinguish between mass and weight.
- Perform Density Calculations.
- Transform a statement of equality to a conversion factor.
- SI measurement
- Le Systeme International d’Unites
- Has seven base units
- Governed by the National Institute of Standards and Technology
- SI Base Units
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Table 2-1 SI BASE UNITS |
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Quantity |
Symbol |
Name |
Ab. |
Defined Standard |
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Table 2-2 SI Prefixes |
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Prefix |
Unit abbreviation |
Exponential factor |
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- Mass- the amount of matter in a given object
- measured by a balance
- compared to a standard set of masses
- Weight- is a measurement of gravitational pull on matter.
- Derived SI Units
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Table 2-3 Derived SI units |
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Quantity |
Symbol |
Unit |
Abb. |
Derivation |
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- Volume- the amount of space occupied.
- Density- The ratio of mass to volume
- Density = Mass/ Volume
- Sample problem 2-1 pg. 39
- Conversion Factors- is a ratio derived from the equality between two different units that can be used to convert from one unit to the other.
- This is the most important math skill in chemistry.
- Commonly called FACTOR LABEL METHOD
- ALWAYS PUT A MULTIPLICATION SYMBOL AND LINE.
- Practice below Pg 41 sample problem 2-2
Section 2-3
Using Scientific Measurements
Objectives
- Distinguish between accuracy and precision
- Determine the number of significant figures in measurements.
- Perform mathematical operations involving significant figures.
- Convert measurement into scientific notation.
- Distinguish between inversely and directly proportional relationships.
- Accuracy and Precision
- Accuracy- how close one is to the answer
- Precision- refers to the range of the measurements. Do you constantly get the same answer?
- Percent Error- a measurement that states how good one’s answer is.
a. Percent error =
((Accepted value – Experimental value) ¸ Accepted Value) X 100%
b. Practice problem 2-3 page 45
- Significant Figures- in a measurement consists of all the digits known with certainty plus one final digit, which is somewhat uncertain or is estimated.
- What numbers are measured?
- What numbers are important?
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Table 2-5 Rules for Determining Significant Zeros |
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Rule |
Example |
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- Rounding- pg 48
- Addition or subtraction- answer must have the same number of decimal places as the number with the fewest decimal places.
- Multiplication and Division- Answer must have the same number of digits as the number with the fewest number of sig figs.
- Scientific notation- numbers written in the form M X 10 n
- 1 < M > 10
- n is some whole number
- Using Sample problems pg. 52
- Direct Proportions- when dividing one by the other produces a constant value
1. The variables will do the same
- Inverse proportions- when the product is constant.
1. The variables will do the opposite.