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Measurement review

HIGHLAND PARK CHEMISTRY. Measurement review. Uncertainty in Measurements. Different measuring devices have different uses and different degrees of accuracy. Significant Figures. The term significant figures refers to digits that were measured.

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Measurement review

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  1. HIGHLAND PARK CHEMISTRY Measurementreview

  2. Uncertainty in Measurements Different measuring devices have different uses and different degrees of accuracy.

  3. Significant Figures • The term significant figures refers to digits that were measured. • When rounding calculated numbers, pay attention to significant figures so the accuracy of answers is not overstated

  4. Significant Figures • All nonzero digits are significant. (5288) • Zeroes at the beginning of a number are never significant(0.084) • Zeroes between two significant figures are themselves significant. (88084) • Zeroes at the end of a number are significant if a decimal point is written in the number.(88.084)

  5. Significant Figures • When addition or subtraction is performed, answers are rounded to the least significantdecimal place. • When multiplication or division is performed, answers are rounded to the number of digits that corresponds to the least number of significant figures in any of the numbers used in the calculation.

  6. Scientific Notation • Chemistry deals with very large and very small numbers. • There are 602,000,000,000,000,000,000,000moleculesof water in 18 mL • one electron has a mass of 0.000000000000000000000000000911 g • We need a shorter way of writing these numbers

  7. Standard Exponential Form • another name for scientific notation. • consists of two parts • a number between 1 and 10 and • multiplied by 10, raised to some power • 602,000,000,000,000,000,000,000 = 6.02 x 1023 • 0.000000000000000000000000000911 g = 9.11 x 10-28

  8. Putting a number into scientific notation • determine how many times you have to move the decimal place to make it into a number between 1 and 10 • 3240000 (LP) • use that as the power of 10 • 3.24 x 106

  9. What if the number is smaller? • if you make the number bigger by moving the decimal point, make the exponent smaller and visa-versa • 0.00045 (RN) • 4.5 x 10-4

  10. SI Units • Système International d’Unités • Uses a different base unit for each quantity

  11. Metric System Prefixes convert the base units into units that are appropriate for the item being measured.

  12. Volume • The most commonly used metric units for volume are the liter (L) and the milliliter (mL). • A liter is a cube 1 dm long on each side. • A milliliter is a cube 1 cm long on each side.

  13. Mass • Weight is a force. Mass is the amount of matter. • 1 gram is defined as the mass of 1 cm3 of water at 4 ºC. • 1000 g = 1000 cm3 of water • 1 kg = 1 L of water

  14. Mass • 1 kg = 2.5 lbs • 1 g = 1 paper clip • 1 mg = 10 grains of salt

  15. Temperature: A measure of the average kinetic energy of the particles in a sample.

  16. Temperature • Scientific measurements: Celsius and Kelvin scales used most often • Celsius scale is based on properties of water. • 0C is the freezing point of water. • 100C is the boiling point of water.

  17. The Fahrenheit scale is not used in scientific measurements. • F = 9/5(C) + 32 • C = 5/9(F − 32) Temperature • The Kelvin is the SI unit of temperature. • There are no negative Kelvin temperatures. • K = C + 273.15

  18. Or USE ONE FORMULA F = 1.8C + 32

  19. Dimensional Analysis • Dimension = unit • Analyze = solve • Using the units to solve the problems. • If the units of your answer are right, chances are you did the math right.

  20. Dimensional Analysis • A ruler is 12.0 inches long. How long is it in cm? ( 1 inch is 2.54 cm) • in meters? • A race is 10.0 km long. How far is this in miles? • 1 mile = 1760 yds • 1 meter = 1.094 yds • Pikes peak is 14,110 ft above sea level. What is this in meters?

  21. Dimensional Analysis • Another measuring system has different units of measure. 6 ft = 1 fathom 100 fathoms = 1 cable length 10 cable lengths = 1 nautical mile 3 nautical miles = 1 league • Jules Verne wrote a book 20,000 leagues under the sea. How far is this in feet?

  22. 1 m 1 m 1 m 1 m 100 cm 100 cm 100 cm 100 cm 3 Units to a Power • How many m3 is 1500 cm3? 1500 cm3 1500 cm3

  23. Units to a Power • How many cm2 is 15 m2? • 36 cm3 is how many mm3?

  24. 65 mi hr Multiple units • The speed limit is 65 mi/hr. What is this in m/s? • 1 mile = 1760 yds • 1 meter = 1.094 yds 1760 yd 1 m 1 hr 1 min 1 mi 1.094 yd 60 min 60 s

  25. Multiple units • Lead has a density of 11.4 g/mL. What is this in pounds per quart? • 454 g = 1 lb • 1 L = 1.094 qt

  26. Density • How heavy something is for its size. • The ratio of mass to volume for a substance. • D = M / V • Independent of how much of it you have • gold - high density • air low density.

  27. m V d= Density: Physical property of a substance

  28. Platinum Mercury Aluminum DENSITY - an important and useful physical property 13.6 g/cm3 21.5 g/cm3 2.7 g/cm3

  29. Calculating • The formula tells you how. • Units will be g/mL or g/cm3 • A piece of wood has a mass of 11.2 g and a volume of 23 mL what is the density? • A piece of wood has a density of 0.93 g/mL and a volume of 23 mL what is the mass?

  30. Floating • Lower density floats on higher density. • Ice is less dense than water. • Most wood is less dense than water. • Helium is less dense than air. • A ship is less dense than water.

  31. Density of water • 1 g of water is 1 mL of water. • density of water is 1 g/mL • at 4ºC • otherwise it is less

  32. Problem A piece of copper has a mass of 57.54 g. It is 9.36 cm long, 7.23 cm wide, and 0.95 mm thick. Calculate density (g/cm3).

  33. Strategy 1. Get dimensions in common units. 2. Calculate volume in cubic centimeters. 3. Calculate the density. (9.36 cm)(7.23 cm)(0.095 cm) = 6.4 cm3 Note only 2 significant figures in the answer!

  34. Error • Accepted value – The right answer • Based on reliable references • Experimental Value- what you get in lab • Error= experimental value – accepted value • Can be negative

  35. Percent Error [Accepted – experimental] • Absolute value of error • I know that I weigh 215 kg. If I weigh myself and the balance says 210 kg, what is the percent error?

  36. Accuracy versus Precision • Accuracy refers to the proximity of a measurement to the true value of a quantity. • Precisionrefers to the proximity of several measurements to each other.

  37. Can you hit the bull's-eye? Three targets with three arrows each to shoot. Both accurate and precise Precise but not accurate Neither accurate nor precise How do they compare? Can you define accuracy and precision?

  38. Accuracy:degree to which the measurement agrees with the accepted ( known) value. • Precision: degree to which the individual measurements agree with each other. • Accepted Value: 47.32 g • Student A B C • Weigh 1 47.13 47.45 47.95 • 2 47.94 47.39 47.95 • 3 46.83 47.42 47.89 • 4 47.47 47.41 47.93 A = Not accurate Not precise (range is too large) B = Accurate and Precise C = not accurate, precise (real close to each other)

  39. Qualitative / quantitative • Qualitative Measurements = results in descriptive, non-numeric form Ex. basketball is brown Surface of basket ball has indented seams • Quantitative Measurments = results in definite form, numbers/units Ex. Diameter of BB is 31 inches Air Pressure in BB is 12 pounds/ square inch

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