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Homework

This homework assignment involves reading pages 11-13 and solving problems from Chapter 1, including significant figures and scientific notation.

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Homework

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  1. Homework • Read Pgs. 11-13 • Chapter 1 Problems 20, 24, 26,30 • Worksheet Scientific Measurement (2A Extra Practice Problems)

  2. Significant figures Addition and Subtraction • The answer must have the same number of decimal places as the factor with the least number of decimal places.

  3. Significant Figures Example of Addition: 1250 + 23.98 1273.98 (this is what a calculator will show) 1274 (this is the answer corrected for significant figures, rounded to the 1’s place)

  4. Significant figures Multiplication and division • The answer must have the same number of significant figures as the factor with the least number of significant figures.

  5. Significant figures Example of Division: 15.375 / 5.0 = 3.075 (this is what a calculator will show) Since the denominator only has 2 significant figures the answer is rounded to 3.1

  6. Significant Figures • 8.654 m x 0.34 m = • 2.10 cm x 0.50 cm = • 10.4815 ml ÷ 8.4 ml = • 0.365 m ÷ 0.050 m =

  7. textbook HW 20a. 3 26a. 132.5 g b. 4 b. 298.69 cm c. 4 c. 13 lb d. 1 d. 350 oz e. 5 30. only c is exact 24a. 0.5 b. 401.4 c. 0.2684 d. 7.8

  8. Scientific Measurement 1 a. 3 2 a. 133 g e. 50.8 dm b. 4 b. 109 mL f. 2.86x103 cal c. 7 c. 13 cm d. 2 d. 14 g/mL e. 3 f. 6 3 a. 1.0 e. 740. 4a. 145g e. 1.30x102dm b. 40.1 f. 80 b. 64mL f. 16 cm c. 6.2x10-5 c. 91.7 cm2 g. 6000cal d. 1.5 d. 4.3g/cm3

  9. Unit 1 • Read pages 8-9 • Unit 1 Sci. Notation and % Error • Chapter 1 Problems 20, 24, 26,30 • Quiz: Oct 18/19 (Thursday / Friday)

  10. Numbers and Measurement • Chemistry requires us to make accurate measurements that are often very small or very large. • To more easily handle these very large and small numbers, we use scientific notation.

  11. Scientific Notation • Measurements are written as the product of two numbers • A coefficient – number between 1 and 10 • 10 raised to a power – the exponent indicates the number of times the coefficient must be multiplied or divided by 10.

  12. Scientific Notation • Write the following in scientific notation: • 6,954,000 • 175.983 • Write the following in standard numerical form: • 6.75 x 10-3 • 1.865 x 102

  13. Calculations in Scientific Notation • Multiplication • Multiply coefficients • Add exponents • Perform the following calculations: • 7.2 x 102· 5.02 x 10-3 • 1.0 x 102· 2.6 x 108

  14. Calculations in Scientific Notation • Division • Divide coefficients • Subtract the exponent of the denominator from the exponent of the numerator. • Perform the following calculations: • 8.4 x 103 / 2.1 x 10-2 • 7.25 x 104 / 5.0 x 102

  15. Calculations in Scientific Notation • Addition and subtraction • Make the exponent of both numbers the same • Align decimal points, and add coefficients • The exponent of the result will be the same as for the measurements

  16. Calculations in Scientific Notation • Perform the following calculations: • 6.3 x 104 + 2.1 x 10-3 • 7.563 x 102 - 1.77789 x 10-3

  17. Calculations in Scientific Notation • 1.5 x 106 + 2.7 x 103 • 6.38 x 10-3 – 3.8 x 10-4

  18. International System of Units

  19. SI Units • 103 for kilo- k • 106 for mega- M • 109 for giga- G • 10-1 for deci- d • 10-2 for centi- c • 10-3 for milli- m • 10-6 for micro- μ • 10-9 for nano- n • 10-12 for pico- p

  20. Accuracy: Evaluations of Measurements • Accepted value: True or correct value based on reliable source • Experimental value: measured by you during the experiment

  21. Error • Difference between the accepted value and the experimental value • Take the absolute value

  22. % Error % Error = Error / accepted value * 100 % Error = Actual – Experimental x 100 Actual

  23. What is the % error? • A student measures a volume as 25.0mL, whereas the correct volume is 23.2mL.

  24. Density • Which is heavier – a pound of popcorn or a pound of cheese? • They would have the same mass!! • However, if you had equal VOLUMES of popcorn and cheese, the cheese would have more mass.

  25. Density • A cube of gold-colored metal with a volume of 64 cm3 has a mass of 980. grams. The density of pure gold is 19.3 g/cm3. Is the metal pure gold?

  26. Unit 1 • HW: Read pages 9-10 • Unit 1: Density and Temperature • More Conversion Problems

  27. Temperature • The temperature of an object determines the flow of heat transfer. • Celsius scale uses the freezing point of water as 0 and the boiling point of water as 100. • Kelvin scale uses 273 for the freezing point of water, and 373 as the boiling point.

  28. (Gabriel) Fahrenheit Scale • German physicist • Developed scale in 1714 • Hg was used in thermometer • Freeze pt. water = 32˚F • Boiling pt. water = 212˚F • 0˚F = freeze pt. of water, salt and dry ice (CO2)

  29. Why use Hg in a thermometer? • For every degree the mercury’s temp. increases, the difference in which the Hg expands is NOTICABLE and CONSTANT. • Alcohol thermometer used in Alaska because Hg will freeze!

  30. (Anders) Celsius Scale • Developed in 1742 • Swedish Astronomer • Freezing pt. of water = 0˚C • Boiling pt. of water = 100˚C • Uses Hg in thermometer

  31. (Lord William) Kelvin Scale • Developed in 1848 • Based on absolute zero = zero heat energy = all motion stops • 0 Kelvin = -273.15˚C • No degree on scale (Kelvin units) • Kelvin is a theoretical scale because it does not compare the temp. to FP or BP of water. • Based on lowest temperature possible – No negative numbers on scale

  32. Compare the 3 temperature scales

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