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Ch.1 lecture a


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1/9/13 Lecture on Matter and Measurements

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Ch.1 lecture a

  1. 1. 1/9/2013CHM 101 Chapter 1: Matter & Measurement
  2. 2. Classifying Matter Matter is anything that has mass and A mixture is 2 or more takes up volume substances physically A pure substance has a fixed or definite mixed, but not composition chemically combined.Element - Contains Compound – combinationonly 1 type of atom of 2 or more elements always in same ratio
  3. 3. Classifying MatterIdentify each of the following pure substances as examples of elements or compounds.
  4. 4. States of MatterIdentify general characteristics for each of the three states of matter below(solid, liquid, gas).
  5. 5. Properties of MatterPhysical ChangesIn the example below, water (H2O) is undergoing physical changes, from solid toliquid to gas, but does not change its chemical identity.
  6. 6. Properties of MatterChemical properties identify a substance based on reactions with other substances. Sodium (Na) (and other Group 1A Alkali metals) is known to react violently with water (H2O). 2Na (s) + 2H2O (l)  2NaOH + H2 (g)Chemical changes occur when one substance is converted into a differentsubstance, thus changing the chemical identity. H2 (g) + O2 (g)  2H2O (g)
  7. 7. Chemical Change: Sodium in Water 2Na (s) + 2H2O (l)  2NaOH + H2 (g)
  8. 8. Measurements Measurements always consist of a number and a unit.The numbers in a measurement (measured numbers) should be carefully recordedand reported.From the example above, we know the length of the baby is 53.3 cm. We should useall of the numbers given, but we can’t use any more.
  9. 9. Units of MeasurementWe will primarily usethe metric system ofunits (above).You should know thehighlighted conversions(on the right) to theEnglish system.
  10. 10. Units of Measurement You MUST know the prefixes below and be able to use them as conversion factors. Used torepresent largequantities Used torepresent smallquantities
  11. 11. Precision in Measurements• The tools that we use to measure matter can only be so precise• For example, a ruler only has so many markings on it, which limits one’s ability to determine a precise measurement between markings• This brings us to a dreaded scientific concept: SIGNIFICANT FIGURES!
  12. 12. Significant FiguresExact (Defined) Values have an infinite number of SF’s. 12 eggs = 1 dozen 1 foot = 12 inches Why are we concerned with SF’s?If a reported result is based on several different measurements, the final resultcan be no more precise than the least precise piece of information in thecalculation.For example, if you take the mass of two items as 25.2 g and 1.34 g, how wouldyou report the total mass? 26.54 g or 26.5 g or 27 g????
  13. 13. Significant Figures Rules (You need to memorize these rules and be able to apply them) Rule Example1. All non-zeroes are significant 2.25 (3 significant figures)2. Leading zeroes are NOT significant 0.00000034 (2 significant figures)3. Trailing zeroes are significant ONLY if an 200 (1 significant figure)explicit decimal point is present 200. (3 significant figures) 2.00 (3 significant figures)4. Trapped zeroes are significant 0.0509 (3 significant figures) 2045 (4 significant figures)
  14. 14. Significant Figures Counting Significant Figures Count all digits reading left to right, starting with the first non-zero digit.How many significant figures are in the following measurements? My answer Correct Answer 454 m 0.803 ft 0.0040 g 3000 lb 3000. lb 3.0 x 103 lb
  15. 15. Significant Figures in CalculationsAddition & Subtraction – the number of decimal places in the answer must equal the# of decimal places in the value with the fewest decimal places. Be careful! Your calculator doesn’t care about SF’s!!! You have to decide how many digits to report. 25.2 one decimal place + 1.34 two decimal places 26.54 calculated answer 26.5 answer with one decimal place *Report the sum with the correct number of SF’s: 3.008 g + 0.5 g = ?
  16. 16. Significant Figures in CalculationsMultiplication & Division – the number of SF’s in the answer must equal the numberof SF’s in the value with the fewest SF’s. 110.5 x 0.048 = 5.304 = 5.3 (rounded) 4 SF 2 SF calculator 2 SF *Report the answer with the correct number of SF’s: 8.542 420 = ? Throughout this course you will be expected to report your answers with the correct number of significant figures!!!
  17. 17. Rules for Rounding When the first digit dropped is less than 5 the retained numbers remain the same. 45.832 rounded to 3 significant figures drops the digits 32 = 45.8 When the first digit dropped is greater than 5 the last retained digit is increased by 1. 2.4884 rounded to 2 significant figures drops the digits 884 = 2.5
  18. 18. Rules for Rounding  When the first digit dropped is exactly equal to 5, the last retained digit... … stays the same if it is even. 1.45 rounded to 2 significant figures drops the digit 5 = 1.4 … increases by one if it is odd. 8.350 rounded to 2 sig figures drops the digits 50 = 8.4*Round the following numbers to 4 significant figures:45.38527.29511.00253983.33359 When working a problem, do not round until all calculations are complete. This will avoid introducing round-off errors.