1Review of FundamentalsCHEM-5181Fall 2009Prof. Jose L. JimenezTue 1-Sep-2009Business Items• Discuss syllabus– Time for class on Thu• Sign up for Labs• Fundamentals review used to be a homework, trying clickers this year• Homework assigned later today– Fundamentals• Partially based on clicker responses–TOFMS2Precision vs. Accuracy I• Measure two variables– E.g. concentration of Na+and Cl-in seawater• Accepted value at originXYPrecision vs. Accuracy II• CQ: Which is the most precise?–A–B–C–D– I don’t knowxxxxxxxxxxxxxxxxA B C D3Precision vs. Accuracy III• CQ: Which is the most accurate?–A–B–C–D– I don’t knowxxxxxxxxxxxxxxxxA B C D• Follow up: Which is better, A or B?Precision vs. Accuracy IV• Precision– Agreement between two or more measurements made in an identical fashion• Accuracy– Accuracy is the nearness of a measurement to the accepted valuexCQ: This measurement isA. AccurateB. PreciseC. Precise and AccurateD. NeitherE. I don’t know4Clicker Q• Random errors are often distributed according to the normal error lawNormal Probability Density Function010203040506070800.45 0.47 0.49 0.51Absorbance (unitless)Probability DensityCQ: the probability that theabsorbance is exactly0.49 is:A. 0.49B. 25C. infinityD. zeroE. I don’t knowCLT: http://www.chem.uoa.gr/Applets/AppletCentralLimit/Appl_CentralLimit2.htmlPDF vs CDF• Probability Density vs. Cumulative ProbabilityNormal Probability Density Function010203040506070800.45 0.47 0.49 0.51Absorbance (unitless)Probability DensityNormal Cumulative Probability Function00.20.40.60.811.20.45 0.46 0.47 0.48 0.49 0.5 0.51Absorbance (unitless)Cumulative ProbabilityCQ: the probability that the absorbance is between 0.48 and 0.49 is:A. zero B. It is not definedC. 0.37 D. 0.56E. I don’t know5Fourier AnalysisA. H3is the Fourier transform of h1B. H3is the FT of h2C. H4 is the FT of h1D. B and C are trueE. All are falseh1(t)H3(f)h2(t) H4(f)http://www.chem.uoa.gr/Applets/AppletFourAnal/Appl_FourAnal2.htmlClicker Q• What is the strength of the electric field between two parallel plates at –1000 and 1000 V with respect to ground, if they are separated by 5 mm?A. 2000 TeslaB. 400,000 Volts/meterC. ZeroD. 400,000 Newtons/CoulombE. 2000 Coulombs6Clicker Q• What is the strength of the electric field between two parallel plates at +2000 and +4000 V with respect to ground, if they are separated by 5 mm?A. 2000 TeslaB. 400,000 Volts/meterC. ZeroD. 400,000 Newtons/CoulombE. 2000 CoulombsClicker Q• What is the net electric force on a neutral mercury atom in an electric field of 106V/m? A. It depends on the polarizability of HgB. 1.6 x 10-13NewtonsC. 1.6 x 10-13Newtons / meterD. ZeroE. I don’t know7Clicker Q• What is the force acting on a singly charged (+) potassium ion with zero velocity in a 1 Tesla magnetic fieldA. 1 NewtonB. 1.6 x 10-19NewtonsC. ZeroD. It depends on the relative alignment E. I don’t knowClicker Q• What is true for the distribution of molecular speeds of N2at ambient T & PA. The average speed is ~472 m/sB. The minimum speed is 0 m/sC. The maximum speed is not boundD. None of the aboveE. A, B, and C8Clicker Q• The average thermal speed of SF6at ambient T & P isA. Smaller than that of N2B. Larger than that of N2C. Same as that of N2D. None of the aboveE. A, B, and CClicker Q• Air molecules in this classroom are colliding with each other approximately:A. Once a secondB. 100 times per secondC. 10,000 times per secondD. 106times per secondE. 1010times per second9Clicker Q• The time between collisions for air molecules in an ionizer at a pressure of 10-4Torr is approximately:A. 0.1 nsB. 1 μsC. 100 μsD. 10 msE. 3 sClicker Q• What is the condition for laminar flow in a tube?A. Pressure <= 1 atmosphereB. Reynolds number < 1 C. Reynolds number < 2000D. T < Tcriticaland P<PcriticalE. What is laminar flow?10Clicker Q• What is the vapor pressure of water at 100 degrees C?A. 1012 TorrB. 760 mbarC. 1 barD. 1 atmosphereE. 15 TorrLinear Regression• Standard regression minimizes sum of squared residuals– Residual = vertical distance between datapoint and line• Depending how much scatter there is in the data, the slope and intercept will have more or less error– y = (m ± sm) * x + (b ± sb)– Not displayed in simple regression in Excel• Only gives y = m * x + b–Need to used advanced reg.11The Trouble w/ Standard Regression• Every point pulls the line towards itself– With a weight equal to the squared residual– Noisy points, outliers, can seriously distort fitRegression Demo Program–http://www.vias.org/simulations/simusoft_linregr.html12Example of Non-Parametric Regression• Goal: reduce the pull of outliersA. Green line is a better fitB. Red line is a better fitC. Neither line is a good fitD. The difference in the lines is the uncertainty of the regressionE. I don’t knowhttp://www.chem.uoa.gr/applets/AppletTheil/Appl_Theil2.htmlMore Complete Regression• Nonparametric regression– Does not assume a distribution• Typical linear regression assumes no errors on X, Gaussian errors on Y– More robust in the presence of outliers– http://www.chem.uoa.gr/Applets/AppletTheil/Appl_Theil2.html• Regression with errors in X and Y• Weighted linear regression – Different points have more or less error• Numerical recipes for explanations• Chapters 14 & 15• http://www.nr.com/• Different regressions in many