CHAPTER 2 MEASUREMENTS AND CALCULATION Chemistry

Scientific Method CHAPTER 2 SECTION 1

Scientific Method The 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.

Scientific Method Data  Qualitative  Quantitative  Collected by observation System  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.

Experiment Experimentation allows to test a hypothesis  Controls are the experimental conditions that remainconstant  Variables are any experimental conditions that change Variables:  Dependent: outcome of interest  Independent: what is being changed  Control: what is being kept the same

If phosphorous stimulates corn-plant growth, then corn plants treated with a soluble phosphorous compound should grow faster, under the same conditions as non-treated corn-plants. Figure 2 page 30 Identify: o Hypothesis o Control Experiment o Dependent Variables o Independent Variables o Control Variables

Scientific Method

Hypothesis or Theory Hypothesis  A hypothesis is an explanation for a phenomenon which can be tested in some way.The results can support or reject the hypothesis. Theory  A theory is a broad generalization that explains a body of facts or phenomena. NEVER say “my theory is…”

Inductive and Deductive Reasoning Inductive Reasoning  Start with observations, and through experiment generalize a rule Deductive reasoning  Use rules or axioms to predict the outcome of experiments or the reason behind an observation

Units of Measurement CHAPTER 2 SECTION 2

SI Measurements Scientists all over the world have agreed on a single measurement system called  Le Système International d’Unités, abbreviated SI. SI has seven base units  most other units are derived from these seven

Base SI Units Table 1 page 34

Density and Derived SI Units Metric conversion table Density:  D = m / v Volume:  1 ml = 1 cm 3

Derived SI Units Table 3 page 36

Conversion Factors 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 Dimensional analysis is a mathematical technique that allows you to use units to solve problems involving measurements

Class Work Dimensional Analysis  Find the unit for the volume of a cube where the sides are measured in mm  Find the unit for the speed of a train traveling a certain amount of kilometers over a certain time in hours  Find the unit for the mass of an object where the volume is measured in ml and the density is in g/ml Practice Problem A p 40 Practice Problem B p 42

Using Scientific Measurement CHAPTER 2 SECTION 3

Accuracy and Precision Figure 8 page 44

Percentage Error  PE =[ ( Ve – Va ) / Va ] * 100 Error in Measurement Figure 9 p 46

Class Work Practice Problem C page 45

Significant Figures Table 5 page 47

Significant Figures Adding or subtracting decimals  answer must have the same number of digits to the right of the decimal point as there are in the measurement having the fewest digits to the right of the decimal point Multiplication or division  answer can have no more significant figures than are in the measurement with the fewest number of significant figures.

Rounding Table 6 page 48

Proportions Two quantities are directly proportional to each other if dividing one by the other gives a constant value.

Proportions Two quantities are inversely proportional to each other if their product is constant.

Class Work Practice Problem D page 48 Practice Problem E page 50 Practice Problem F page 54 Practice Problem page 62  Powers of 10