In our daily lives: New materials New pharmaceuticals New energy sources Food supplies Can you think of anything else?
Is the science that deals with the materials of the universe and the changes that those materials undergo
What are some examples of chemical changes? Iron rusting Wood burning Food cooking Grape juice fermenting Plants growing How do we know that these are chemical changes?
1. Observations Quantitative vs Qualitative Quantitative – measurement involves a number and a unit 2. Formulating Hypotheses Possible explanation for the observation 3. Performing Experiments Gathering new information to decide whether the hypothesis is valid
QualitativeQuantitative red book4 quarters round tire6 wheels wooden desk24 students metal chair5 atoms aluminum foil65°C glass square2 x 4 x 8 rough board2 graduated cylinders
Theory (Model) A set of tested hypotheses that give an overall explanation of some natural phenomenon Natural Law The same observation applies to many different systems Ex. Law of Conservation of Mass
A law summarizes what happens; a theory (model) is an attempt to explain why it happens
Scientists must be objective when using the scientific method. The scientific method is affected by: Profit motivesReligious Beliefs WarsMisinterpretation of Data BudgetsEmotions FadsPrejudices PoliticsPeer Pressure
What is the difference between a hypothesis and a theory? What is the difference between an observation and a theory? What is the difference between a natural law and a theory?
Physical Quantity Name Abbreviation mass kilogram kg length meterm time seconds temperature KelvinK Electric Current AmpereA Amount of Substance mole mol Luminous Intensity candela cd
A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty. Measurements are performed with instruments No instrument can read to an infinite number of decimal places.
Accurate and precise Precise, but not accurate Neither accurate not precise Accuracy refers to the agreement between the measure quantity and the accepted value Precision refers to the degree of agreement of several repeated measurements (made in the same manner) to each other.
Random Error (Indeterminate Error) – Measurement has an equal probability of being high or low Systematic Error (determinate Error) – Occurs in the same direction each time (high or low), often resulting from poor technique or incorrect calibration. This can result in measurements that are precise, but not accurate
Non-zero integers always count as sig. fig. 3456 4 sig figs
Zeros Leading Zeros do not count as sig figs 0.0486 3 sig figs
Zeros Captive Zeros always count as sig figs 16.07 4 sig figs
Zeros Trailing Zeros are significant only if the number contains a decimal point. 9.300 4 sig figs
Exact Numbers have an infinite number of significant figures. 1 inch = 2.54 cm
1.0070 m 17.10 kg 100,890 L 3.29 x10 3 s 0.0054 cm 3, 200, 000 5 sig figs 4 sig figs 5 sig figs 3 sig figs 2 sig figs
Multiplication and Division number of sig figs in the results equals the number of sig figs in the least precise measurement used n the calculation (the one with the lowest number of sig figs). 6.38 x 2.0 = 12.76 13 (2 sig figs) 13 (2 sig figs)
CalculationCalculator Says 3.24 m x 7.0 m22.68 m 2 100.0 g ÷ 23.7 cm 3 4.219409283 g/cm 3 0.02 cm x 2.371 cm0.04742 cm 2 710 m ÷ 3.0 s236.6666667 m/s 1818.2 lb x 3.23 ft5872.786 lb·ft 1.030 g ÷ 2.87 mL2.9561 g/mL Answer 23 m 2 4.22 g/cm 3 0.05 cm 2 240 m/s 5870 lb·ft 2.96 g/mL
Addition and Subtraction The number of decimal places in the result equals the number of decimal places in the least precise measurement 6.8 + 11.934 = 18.734 18.7 (3 sig figs) 18.7 (3 sig figs)
CalculationCalculator Says 3.24 m + 7.0 m10.24 m 2 100.0 g - 23.73 cm 3 76.27 g/cm 3 0.02 cm + 2.371 cm2.391 cm 2 713.1 m – 3.827 s709.228 m/s 1818.2 lb + 3.37 lb1821.57 lb·ft 2.030 mL - 1.870 mL0.16 g/mL Answer 10.2 m 76.3 g 2.39 cm 709.2 L 1821.6 lb 0.160 mL