Chem Lab Final Outline - Chem Lab Final Outline Lecture 1 &...

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Chem Lab Final Outline I. Error a. Systematic Error : error that occurs in repeated determinations with the same sign and approximately the same magnitude i. Due to a flaw in the procedure or the experiment ii. Occur repeatedly with about the same magnitude and same sign 1. Ex: leaking buret always administering less and same amount because leak stays same iii. Can be prevented! 1. Ex: stop using the buret because its leaking iv. Error analysis can estimate the magnitude of random errors and find ways to improve the experimental procedures b. Random Error : accidental errors i. Unavoidable ii. Due to limitations of equipment, human error, etc. iii. Taking the average results from multiple trials can improve accuracy c. Absolute Error : The discrepancy between the result and the true value d. Relative Error : The absolute error expressed as a fraction of the average value of the measured quantity i. Relative Error = l absolute error l a. average value ii. Can be expressed part of error in a measurement per hundred (%), per thousand (ppt) or per million (ppm) parts of the quantity measured iii. The larger the measured value, the smaller the relative error e. Error can be anticipated II. Propagation of Error a. Addition and Subtraction i. The relative error of z is the sum of the absolute errors of x and y b. Multiplication and Division i. The relative error of z is the sum of the relative errors of x and y c. Exponential i. If z = a e^(bx), the relative error of z is b times the absolute error in x d. Logarithm i. If z = a ln(x), the absolute error of z is a times the relative error in x ii. If z = log(x), the absolute error of z is III. Significant Figures a. Only report one doubtful digit in an error estimate IV. Ideal Gas Law a. PV=nRT b. R (ideal gas constant or universal gas constant) = PV/nT c. Ideal Gas Behavior: i. The gas molecules are treated as points, not small spheres; i.e. the molecules have zero volume ii. There is no interacting force between the gas molecules iii. There is no loss of kinetic energy when the molecules collide with each other or with the wall of the container; i.e. all collisions are
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elastic V. Dalton’s Law of Partial Pressure a. If gases A and B are in a container, P total = (n A + n B ) RT/V VI. The Siphon Effect a. Siphon = a tube filled with water, the sides of the tube immersed in same liquid but at different levels b. Pressure is exerted on the upper end of tube (P 1 =pgh 1 ) c. Pressure is also exerted on the lower end of the rube (P 2 =pgh 2 ) d. Only works because the two ends of the tubes are subject to atmospheric pressure (P atm pushes down on the bodies of liquid in which the tube is immersed in, therefore affecting the siphon’s pressure by working against P 1 and P 2 ) e. P net = P 2 - P 1 = pg∆h f. For this experiment, i. P flask < P atm because P flask + pg∆h must equal P atm if the liquid does not move ii. To make P flask = P atm , make ∆h=0. iii.
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This note was uploaded on 06/20/2011 for the course CHEM 151 taught by Professor Mao during the Spring '08 term at Washington University in St. Louis.

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Chem Lab Final Outline - Chem Lab Final Outline Lecture 1 &...

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