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CHEMISTRY

CHEMISTRY. July 31, 2012. Brain Teaser (write the question & answer). Convert 100m to cm. Convert 158 kL to L. Convert 85 mg to kg. How many sig digits are in 0.0031324? How many sig digits are in 12.40? How many sig digits are in 386.042? How many sig digits are in 3100.0 x 10^2?.

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CHEMISTRY

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  1. CHEMISTRY July 31, 2012

  2. Brain Teaser (write the question & answer) • Convert 100m to cm. • Convert 158 kL to L. • Convert 85 mg to kg. • How many sig digits are in 0.0031324? • How many sig digits are in 12.40? • How many sig digits are in 386.042? • How many sig digits are in 3100.0 x 10^2?

  3. Introduction to Chemistry Chemistry: The Central Science Chemistry is the science that investigates and explains the structure and properties of matter. Seeks to explain the submicroscopic events that lead to macroscopic observations

  4. Branches of Chemistry

  5. SI Units (Le Systéme Internationale) Scientists need to report data that can be reproduced by other scientists. They need standard units of measurement. Units of measurement Base Units • A base unit is a defined unit in a system of measurement • There are seven base units in SI.

  6. Base Units

  7. Why do we use the (SI) system? Advantages Simple to use Easy to convert from one unit to another Dimensional Analysis Universal – used worldwide By all scientists to communicate By all industrialized nations Except United States U.S. loses billions of dollars in trade

  8. Practice • Convert 10mL to KL • Convert 5.3g to cg

  9. Accuracy and Precision

  10. Data Terms Quantitative Measurements Examples Give results in a definite form, usually values 24L, 10 cm, 14 ºC

  11. Data Terms Qualitative Measurements Examples Give results in a descriptive, non-numeric form. The beaker was warm. The density was greater than that of water.

  12. Data Terms Accuracy Examples How close a measurement comes to the actual value of whatever is being measured Water freezes at 0º C, and boils at 100º C. How close is the measurement to the values.

  13. Data Terms Precision Examples Reproducibility of the measurement 9 out of 10 lab groups report the temperature of boiling water to be 95º C. A basketball player shoots 20 free throws, 18 of which bounce off the right side of the rim.

  14. Accuracy vs. Precision Target Practice Accurate Precise Accurate & Precise

  15. An archery target illustrates the difference between accuracy and precision.

  16. Accuracy and Precision Measurements

  17. Scale Reading and Uncertainty Uncertainty: Limit of precision of the reading (based on ability to guess the final digit). Existed in measured quantities versus counted quantities

  18. Percent error Theoretical – Experimental x 100 = % error Theoretical

  19. SIGNIFICANT FIGURES

  20. Significant Figures Significant Figures Digits in a measurement that have meaning relative to the equipment being used

  21. Significant Figures Place What is the increment on the equipment? What you know for sure.

  22. Significant Figures Digits with meaning Digits that can be known precisely plus a last digit that must be estimated.

  23. Triple Beam Balance (DO NOT USE) http://www.wisc-online.com/objects/index_tj.asp?objID=GCH202 DO NOT USE What are the units?

  24. Ruler http://www.funbrain.com/measure/ What are the units?

  25. Graduated Cylinder http://www.uwplatt.edu/chemep/chem/chemscape/labdocs/catofp/measurea/volume/gradcyl/gradcyl.htm What are the units?

  26. Significant Figures What do you notice? Depends on type of equipment being used. Depends on size of equipment used.

  27. Significant Figures Raw Data Rules How do you know how many sig figs? All digits 1-9 are significant. Zeros between significant digits are always significant. Trailing 0’s are significant only if the number contains a decimal point Zeros in the beginning of a number with a decimal point are not significant. Zeros following a significant number with a decimal are significant.

  28. Significant Figures Pacific to Atlantic Rule Examples Pacific = Decimal Present Start from the Pacific (left hand side), every digit beginning with the first 1-9 integer is significant 20.0 = 3 sig digits 0.00320400 = 6 sig digits 1000. = 4 sig digits

  29. Significant Figures Atlantic Rule to Pacific Examples Atlantic = Decimal Absent Start from the Atlantic (right hand side), every digit beginning with the first 1-9 integer is significant 100020 = 5 sig digits 1000 = 1 sig digits

  30. Practice How many significant figures are in 400.0 4000 4004 0.004

  31. Rally Rows How many significant figures are in 0.02 0.020 501 501.0 5000 5000. 5050 01.0050 50300 5.0300

  32. Review Questions Determine the number of significant figures in the following: 1005000 1.005 0.000125 1000. 0.02002 2002 200.200

  33. Review Questions Determine the number of significant figures in: 72.3 g 60.5 g 6.20 g 0.0253 g 4320 g 0.00040230 g 4.05 x 10^5 g 4500. g

  34. Quick Review What are Significant Digits? Examples Triple Beam Balance Graduated Cylinder All the certain digits plus the estimated digit in a measurement. How many decimal places can we count Hundreths Depends on the size

  35. Significant Figures in Calculations Exact Numbers Examples Infinite # of sig figs Do not affect the number of significant digits in the final answer. They are not measurements!! 1000m = 1 km 12 in = 1 foot

  36. Significant Figures in Calculations Multiplication and Division Example The number with the smallest number of significant digits determines how many significant digits are allowed in the final answer. Volume of a box L x W x H (3.05m)(2.10m)(0.75m) 2 sig figs 4.8m3

  37. Significant Figures in Calculations Example Density of a penny M = 2.53g V = 0.3mL D = M / V # significant figures allowed D = 8g/mL

  38. Significant Figures in Calculations Addition and Subtraction Example The number of significant digits depends on the number with the largest uncertainty. (you may be using different scales) Shoes 951.0 g Clothes 1407 g Ring 23.911 g Glasses 158.18 g Total 2540. g

  39. Significant Figures in Calculations Example What is the mass of a penny if, the weighing paper alone has a mass 0.67 g and weighing paper plus the penny has a mass of 3.2 g. 3.2 g -0.67 g 2.5 g

  40. Significant Figures in Calculations Remember A calculated number can only be as precise as the least precise measurement in the calculation.

  41. Practice Calculate each of the following to the correct number of significant figures. Include units on your answer. (25 g/mol)(4.0 mol) = (3.48 in)(1.28 in)(0.010 in) = 2.06 cm + 1.8 cm + 0.004 cm = If the mass of a lead cube is 176.91 g and it measures 2.51cm x 2.49 cm x 2.49 cm, what is the density of lead?

  42. Practice Calculate each of the following to the correct number of significant figures. Include units on your answer. (25 g/mol)(4.0 mol) =1.0 x 102 (3.48 in)(1.28 in)(0.010 in) = .045 in3 2.06 cm + 1.8 cm + 0.004 cm = 3.9 cm If the mass of a lead cube is 176.91 g and it measures 2.51cm x 2.49 cm x 2.49 cm, what is the density of lead? 11.3 g/cm3

  43. Rally rowsSig figs in Calculations 12 cm + 0.031cm + 7.969 cm = (41.025 g - 23.38g) ÷ 8.01 mL= 17.3 cm x 6.2 cm + 3.28 cm2 = 109.3758 m2  45.813 m = What is the mass of Salt (NaCl) if the sodium has a mass of 22.99 g and the Cl a mass of 35.5g?

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