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So yesterday we talked about experiments, but…

So yesterday we talked about experiments, but…. Experiments Don’t Always Go According to Plan. Accidental Discoveries Teflon (page 48) Mauve clothing dye (Page 49). Theories and Laws.

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So yesterday we talked about experiments, but…

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  1. So yesterday we talked about experiments, but…

  2. Experiments Don’t Always Go According to Plan • Accidental Discoveries • Teflon (page 48) • Mauve clothing dye (Page 49)

  3. Theories and Laws • When a hypothesis withstands repeated testing, it may become a theory – a well-tested explanation of observations • Theories are explanations, not facts • They can be disproved, but can never be completely proven. • Law is a statement or mathematical expression that reliably describes a behavior in the natural world

  4. The main difference While a theory is an attempt to explain the cause of certain events in the natural world, a scientific law describes the events

  5. Models • A model is a representation of an object, a system, a process, or an idea. • A model is used to help describe or communicate information about ideas or theories that are difficult to observe or explain otherwise.

  6. Dimensional Analysis Using Conversion Factors

  7. Système Internationale d’Unitès Units • There are 7 SI Base Units

  8. In Chemistry, we must remember to use a number (quantity) and unit (abbreviation) In other words, 5 is usually only half the answer.

  9. Something else to consider • These base units may be too large or small depending on the situation • Therefore we need to use dimensional analysis – conversion factors • For this we need: • Prefixes (page 13; Table 3) • Equalities • Sometimes more than one

  10. Helpful Chart to remember Smaller Bigger deci (d) 10 deca (da) centi (c) 100 (hecto, h) milli (m) 1000 kilo (k) Micro (m) 1000000 mega (M) nano (n) 1000000000 giga (G)

  11. Let us look at some examples 0.765 g to kg 1 kg 0.765 g x = 0.000765 kg 1000 g 1) Rewrite what is given 2) Set up the equalities so that the unit you start with is canceled out and the new one is left. 3) Fill in the numerical values 4) Multiply by the top numbers; divide by the bottom numbers

  12. Sometimes 2 steps are needed 23745 kg to milligrams 1000 mg 1000 g 23745 kg x x = 1 1 kg g 23745000000 mg

  13. Try the Problems on the Metrics and Measurement Worksheet Groups 1, 3, 5, and 7 do the odd problems Groups 2, 4, 6 and 8 do the even problems

  14. 0.35 0.950 27.5 1 1 4.5 250 0.5 7.5 15,000 Answers to those problems

  15. Derived Units • These units are derived by multiplying or dividing the base units. • Examples • Speed – m/s • Area – m2 • Volume – m3, but scientist tend to use the L or mL *1cm3 = 1mL • Density = g/mL (D=m/V)

  16. Example Density Problems(from page 858) 16) What is the density of an 84.7 g sample of an unknown substance if the sample occupies 49.6 cm3? 17) What volume would be occupied by 7.75 g of a substance with a density of 1.70766 g/cm3?

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