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Chemistry Chapter 3

Chemistry Chapter 3. Scientific Measurement. A) 241 2.41 x 10 2 B) 6015 6.015 x 10 3 C) 0.0162 1.62 x 10 -2. D) 0.512 5.12 x 10 -1 E) 6.62 x 10 2 662 F) 3.4 x 10 -3 0.0034. Scientific Notation Convert to or from Scientific Notation:.

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Chemistry Chapter 3

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  1. Chemistry Chapter 3 Scientific Measurement

  2. A) 241 2.41 x 102 B) 6015 6.015 x 103 C) 0.0162 1.62 x 10-2 D) 0.512 5.12 x 10-1 E) 6.62 x 102 662 F) 3.4 x 10 -3 0.0034 Scientific NotationConvert to or from Scientific Notation:

  3. Accuracy -how close measurements are to the correct or accepted value. Precision - closeness of a set of measurements.

  4. Percent error – compares the accuracy of an individual value or average values to the correct or accepted value.

  5. % error = Accepted value – Experimental value x 100% Accepted value STAAR CHART FORMAT

  6. Example: What is the percent error for a mass measurement of 17.7g, given that the correct value is 21.2g? % error = 21.2g – 17.7g x 100% = 21.2g 16.5%

  7. Significant Figures Rules 1. Nonzero Digits – every nonzero digit is significant. Ex: a) 32.8 m has three sig figs b) 981.78 km has five sig figs

  8. 2. Sandwich zeros – zeros appearing between nonzero digits are significant. Ex: c) 101.2 g has four sig figs d) 50.1 L has three sig figs

  9. 3. Placeholder – leftmost zeros appearing in front of nonzero digits are not significant. Ex: e) 0.000007 has one sig fig f) 0.0003809 has four sig figs

  10. 4. Trailer zeros – zeros at the end of a number and to the right of the decimal point are significant. Ex: g) 2000. m has four sig figs h) 34.0 mL has three sig figs Uncertainty in Measurement

  11. STAAR CHART FORMAT FOR SIG. FIGS.

  12. Rounding *The calculated value cannot be more precise than the measured values used to obtain it.

  13. a) 45.89m 45.9m b) 3004 m 3.00 x 103m c) 17.32 cm 17.3 cm d) 20019 L 2.00x104 L Example: Round each measurement to the three sig. figs.

  14. Rounding – Addition and Subtraction Round the answer to the same number of decimal places (not digits) as the measurement with the least number of decimal places.

  15. Example: Subtract 2.6103m from 5.44m. 5.44 m - 2.6103 m 2.8297 m 2.83m

  16. Rounding – Multiplication and Division Round the answer to the same number of sig. figs as the measurement with the least number of sig. figs.

  17. Example: Multiply 2.4 m2 and 15.82m. 2.4 m2 x 15.82 m = 37.968 m3 38 m3 Extra Practice

  18. SI Measurement – Le Systeme International d’Unites

  19. 7 SI Base Units

  20. SI Prefixes

  21. Mass – measure of the quantity of matter (SI unit is kg). The gram, g, is ideal for expressing masses of small objects such as a beaker. For even smaller masses like weighing out chemicals the milligram is used.

  22. Mass vs Weight Mass is the measure of the amount of matter, whereas weight is the measure of the gravitational pull on matter.

  23. Derived units are a combination of SI base units. *Volume is the amount of space occupied by an object. The derived unit for volume is cubic meters, m3. (Volume = l x w x h)

  24. Figure 01.20

  25. Density is a derived unit. It is mass divided by volume. density = mass or D = m volume V The SI units are kg/m3

  26. Density…: • is a physical property of a substance. • does not depend on the size of the sample. • As the mass of the sample increases so does the volume.

  27. Density of a substance determines whether it floats or sinks in a liquid. For instance, ice has a density of 0.92 g/mL, which is less than that of water (0.998 g/mL). Since ice is less dense, it will float on water.

  28. Example: The density of water is 0.998 g/mL. If copper pellets were placed in the water would it sink or float? (Density of copper is 8.92g/mL) The copper would sink as its density is higher than that of water.

  29. Examples:A sample of aluminum metal has a mass of 8.40g. The volume of the sample is 3.1cm3. Calculate the density of aluminum. D = m = 8.40g = 2.7g/cm3 V 3.1cm3

  30. A sheet of metal has a length of 32.0cm, a width of 2.00cm, and a height of 1.000cm. The density of the metal is 9.7g/cm3. Calculate the mass of the metal. D = m/V m = D x V m = (9.7g/cm3)(32.0cm x 2.00cm x 1.000cm) m = 620 g

  31. Specific Gravity • Comparison of the density of a substance with the density of a reference substance. • A hydrometer is used to measure the specific gravity of a liquid.

  32. Temperature • Determines the direction of heat transfer.

  33. Temperature Scales • Celsius scale: Uses water as the reference (i.e. 0oC and 100oC)

  34. Temperature Scales (cont.) • Kelvin scale: Freezing point of water is 273.15 K and its boiling point is 373.15 K. • Absolute Zero – all motion ceases

  35. Converting between Celsius and Kelvin K = oC + 273 oC = K – 273

  36. Liquid nitrogen boils at 77.2 K. What is this temperature in degrees Celsius? oC = K – 273 oC = 77.2 – 273 -195.8oC

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