Chapter 3

1. Chapter 3 Measurements

2. Scientific method is a series of steps followed to solve problems, including • Observations • Proposing and testing hypotheses • Developing theories/Laws • A scientist chooses which set of steps to use depending on the nature of the investigation.

3. Making Observations • Questioning → Problem • Identify the problem (What is causing the problem?) • Hypothesis • Educated guess; “If….then….”

4. Testing Hypotheses • Through Experiment • Independent Variable – thing you change in the experiment (ex: put a plant in dark room/light room) • Dependent Variable – the factor that changes; observed during exp.(plant dies, does or does not grow) • Control – the part of the experiment that does not get the IV (placebo) • Constants – factors that remain the same (water plants equally) Developing Theories/Laws Hypothesis – correct or incorrect?

5. Theory • A theory is a well-tested explanation of observations. • Theories are explanations, not facts, so they can be disproved but can never be completely proven • Ex: big bang theory, kinetic theory of gases, quantum field theory, atomic theory, human evolution theory, caloric theory

6. Law • A law is a statement or mathematical expression that reliably describes a behavior of the natural world. • These are fact that always hold true. Law of Universal Gravitation, Law of Conservation of energy, Law of conservation of mass

7. Hypothesis A hypothesis may be revised based on experimental data. Observations Theory A theory is tested by more experiments and modified if necessary. Experiments An experiment can lead to observations that support or disprove a hypothesis. Scientific Law A scientific law summarizes the results of many observations and experiments. Comparing hypothesis, theories and laws • A hypothesis – predicts an event • A theory – explains it • A law – describes it

8. What is a hypothesis? A. information obtained from an experiment B. a proposed explanation for observations C. a concise statement that summarizes the results of many experiments D. a thoroughly tested model

9. What is a hypothesis? A. information obtained from an experiment B. a proposed explanation for observations C. a concise statement that summarizes the results of many experiments D. a thoroughly tested model

10. Measurement is a quantity that has both a number and a unit. Ex: Your height (66 inches), your age (15 years), and your body temperature (37°C) Chemistry: A single gram of hydrogen, for example, contains approximately 602,000,000,000,000,000,000,000 hydrogen atoms.

11. Scientific Notation a given number is written as the product of two numbers: a coefficient and 10 raised to a power. Ex: 602,000,000,000,000,000,000,000 can be written in scientific notation as 6.02 x 1023. • The coefficient in this number is 6.02. The power of 10, or exponent, is 23. 94,700. = 9.47 x 104 0.00736 = 7.36 x 10–3

12. Do Now 55000 5.5 x 104 positive exponent 477 4.77 x 102 80,000,000 8 x 107 0.006 6 x 10-3 negative exponent 0.010 1.0 x 10-2

13. Accuracy vs Precision Accuracy • how close you are to the right answer Precision • Reproducing the same answer over and over (regardless if it is correct or not) Poor Accuracy, Good Precision Good Accuracy, Good Precision Poor Accuracy, Poor Precision

14. Which one is more precise? WHY? Beaker

15. Do Now What units would commonly be used to express the below quantity? • Length or distance: • Weight: • Volume: • Time: • Temperature: • Electric current: • Potential differences: • Heat:

16. Do Now What units would commonly be used t0 express the below quantity? • Length or distance: inches, feet, yard, miles (SI: meter m) • Weight: pounds, ounces, tons • Volume: gallons, cups, teaspoons, tablespoons, fluid ounces (SI: liter l) • Time: days, years, hours, minutes, seconds (SI: seconds s) • Temperature: degrees Fahrenheit, degrees Celsius (SI: Kelvin K) • Electric current: amperes (SI: ampere A) • Potential differences: volts • Heat: British thermal units (BTU) • *note: heat & temperature is different

17. International System of Units • Derived units are used for measurements such as volume, density, and pressure.

18. Mass Weight • a measure of the amount of matter in an object • a measure of gravitational force exerted on an object

19. Heat Energy transferred between objects that are at different temperatures. Heat energy is always transferred from a warmer object to a cooler object Energy Can Be Released As Heat • heat energy is transferred from the water to the ice • energy that is stored within the reacting chemicals are being released

20. Temperature • is a measure of the average KE of the particles in an object (how fast particles vibrate). • Boiling water • Energy from heating caused water molecules to move faster (more KE) • As you heat more, average KE increases so temperature increases • temperature change of the water is a measure of the energy transferred from the stove as heat

21. Temperature scale Celsius: 0°C = water freezes; 100°C = water boils **based around water Kelvin: 0 K (no negative #s) Absolute zero: where everything stops moving/vibrating Coldest Temperature = 0 K

22. Convert between the Celsius and Kelvin scales T°C = TK 273.15 K TK = T°C + 273.15°C

23. Converting between K and o C K = 0C + 273 0C = K – 273 Make the following temperature conversions: 25ºC to Kelvin   C  K K = 0C + 273 25 + 273 = 298 K 355K to Celsius K  C ºC = K – 273 355 – 273 = 82 °C

24. Do Now Convert the following: • 25oC to K Ans: 298 K • 300 K to oC Ans: 27oC • 37oC to K Ans: 310 K • 150K to oC Ans: -123oC

25. 10 g 10 g 10 g 10 g 19 cm3 10 cm3 3.7 cm3 0.88 cm3 0.53 g/cm3 1.0 g/cm3 2.7 g/cm3 0.88 g/cm3 mass Density = volume Density ratio of the mass of an object to its volume. Corn oil Water Increasing density (mass per unit volume) Corn syrup

26. Calculating Density • Solve for the unknown

27. How can you convert U.S. dollars to euros? Because each country’s currency compares differently with the U.S. dollar, knowing how to convert currency units correctly is essential. Conversion problems are readily solved by a problem-solving approach called dimensional analysis. CHEMISTRY&YOU

28. Conversion Factors is a ratio of equivalent measurements. For example: 1 dollar = 4 quarters = 10 dimes = 20 nickels = 100 pennies 1 meter = 10 decimeters = 100 centimeters = 1000 millimeters same amount of money same length 1 meter 100 centimeters m Larger unit 1 Smaller number 100 Larger number cm Smaller unit conversion factors

29. Dimensional analysis is a way to analyze and solve problems using the units, or dimensions, of the measurements.