Chpt 2 introduction to chemistry

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  • 1. Introduction to Chemistry: Matter Basic Chemistry Chapter 2 Rev. 1/15/02
  • 2. The study of matter is central to the study of chemistry.Q. What is matter?A. Matter is anything that … … has mass, … and takes up space.
  • 3. What are somethings that are matter?
  • 4. If it’s not matter, what is it? Energy EnergyHeat Light Kinetic energy
  • 5. Do things you cannot see have mass?What about air? How would you experimentally determine that air has mass?A column of air 1 inch square at the base and as tall as the atmosphere, weighs 14.7 pounds at sea level.
  • 6. Consider these statements:The mass of the beaker is 215 grams. The beaker weighs 215 grams.What is the difference between mass and weight?
  • 7. Look at the difference between a balance and a spring scale.A balance compares two masses like a “see-saw”.A spring balance requires a force to stretch the spring.
  • 8. That’s the answer.Weight is a force. To weigh something we must exert an opposing force.Mass is not a force, it is a measure of the quantity of matter.
  • 9. Suppose, on Earth you weigh 60 kilograms. That means that you will also have a mass of 60 kilograms.On the surface of the Earth, mass andweight have the same numericalvalue. Note: 60 kilograms is about 130 pounds.
  • 10. But, if you go to the moon…Take a balance and a spring scale.Even though there is no air on the moon, there is still gravity.The gravity on the moon is 1/6th that of Earth.
  • 11. On the moon …The balance will indicate 60 kilograms,but the spring scale will indicate 10 kilograms …because the force exerted by gravity is 1/6 that of Earth’s.
  • 12. The bottom line …Scientists tend to use “mass” and “weight” interchangeably, even though they know the difference. We will too.Just be sure you know the difference when it shows up on a test.
  • 13. Where will you weigh more? (a) Mt. Everest (b) Myrtle Beach (c) The bottom of a South African diamond mine
  • 14. The Metric System
  • 15. What are the basic units of mass, length, volume,temperature and time in the metric system?
  • 16. The metric system …Mass Gram gLength Meter mVolume Liter LTemperature Kelvin KTime Second s
  • 17. What are the commonly used metric prefixes?Mega- x 106 megabyte, megohmKilo- x 103 kilometer, kilogramCenti- x 10-2 centimeterMilli- x 10-3 millimeter, milligramMicro- x 10 -6 micrometer, microgramNano- x 10 -9 nanometer
  • 18. What are the symbols for the metric prefixes? Mega- M - MB, MΩ Kilo- k - km, kg Centi- c - cm Milli- m - mm, mg, mL Micro- µ - µm, µg, µL Nano- n - nm
  • 19. Density
  • 20. What is density?Density is the ratio of the mass m of an object to D= the volume of V the object. Typical units of density are grams per milliliter, g/mL
  • 21. Does the density of a substance depend on the amount of substance?No. The ratio is a constant. As you add more mass of the substance, the volume increases as well.
  • 22. Does the density of a substance depend on the temperature of the substance?Yes. But only slightly for solids and liquids. As the temperature changes, expansion and contraction occurs, which changes the volume slightly, but …
  • 23. The density of a confined gaschanges dramatically as thetemperature changes… … because thevolume of a gasdepends on the Gastemperature. Cylinder with movable piston hotplate
  • 24. Develop a method to measure the density of a piece of metal.What equipment will you need? What data should you take?How will you analyze the data?
  • 25. Devise a method to measure the density of a liquid.What laboratory equipment will you need? What kind of data should you take?How will you analyze the data?
  • 26. How can youmeasure thevolume of anodd-shapedsolid?
  • 27. Hint: ArchimedesEureka!
  • 28. Liquid Displacement An object will displace its own volume of water.
  • 29. Devise a method to measure the density of a metal cylinderWhat equipment will you need? What data should you take?How will you analyze the data?
  • 30. MeasurementsAccuracy and Precision
  • 31. Consider four targets and three shots on each:Low Precision High PrecisionLow Accuracy Low Accuracy Low Precision High Precision High Accuracy High Accuracy
  • 32. Precision vs AccuracyPrecision – the reproducibility of the measurementAccuracy – the closeness to the correct answer
  • 33. Precision is indicated by … An uncertainty in the measurement 5.4 +/- 0.2 mL 34.56 +/- 0.01 g 19.3 +/- 0.1 cm It wouldn’t make sense to write a volume as 15.675 mL when the graduated cylinder is only precise to the nearest mL: +/- 1 mL
  • 34. Precision is also indicated … … by the number of significant digits in a measurement. 14.7 has 3 significant digits 1004 has 4 significant digits 200. has 3 significant digits 0.0046 has 2 significant digits 204.70 has 5 significant digits
  • 35. Rules for Significant Digits1. All non-zero digits are significant.2. Zeroes between non-zero digits are significant.3. Zeroes which are place holders are not significant, unless otherwise indicated.4. Zeroes which indicate the level of precision are significant.
  • 36. Examplesa. 243.5 a. 4b. 0.0405 b. 3c. 1,900 c. 2d. 100. d. 3e. 0.00360 e. 3f. 304.50 f. 5
  • 37. Precision in calculations: The answer can have no more precision that the least precise factor. In other words: the answer has the same number of significant digits as the value with the lowest number of significant digits.
  • 38. Multiply 3.5 cm by 0.251 cm to get the area.The calculator gives 0.8785 cm2 But we write the answer as 0.88 cm2 3.5 has two significant digits, and 0.251 has three significant digits … the answer can only have two significant digits. 0.88 cm2
  • 39. A student finds a side of a rectangle to be 3.69 m and another student finds the other side to be 12 m. Find the area of the rectangle. A=LxW A = 3.69 m x 12 m A = 44 m2Not 44.28, since the answer can have only two significant digits.
  • 40. Do the following calculations andexpress the answer to the correctnumber of significant digits.1. 45.3 x 0.0031 = 0.142. 0.0850 x 32.2 = 2.743. 65.0 / 20.30 = 3.204. (7.3 x 103)( 3.030 x 104) = 2.2 x 1085. 360 / 12 = 30.
  • 41. TemperatureMeasurements
  • 42. Temperature is ameasure of “how hotor cold” something is. How do we measure temperature?
  • 43. Thermometer Temperature probeThermocouple Color
  • 44. Temperature ScalesK C F Boiling point373 100 212 of water Freezing point of water273 0 32 (Melting point of ice) Absolute zero0 -273 -462 (Coldest possible temp.)
  • 45. Temperature Conversions K = C + 273 F = 1.8 C + 32
  • 46. In later projects we will study heat transfer, conservation of energy,and measure the specificheat capacity of a metal.
  • 47. Things to find out about: Temperature and heat changes The “Law of Conservation of Energy” Specific heat capacity The equation Q = mc∆T A procedure to measure the mass and volume of a solid cylinder of metal. A procedure to measure the specific heat capacity of the metal.
  • 48. Next presentation: Chpt 3 - EnergyClick on the link below: Energy