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More on “Signal”
• Interference• Method blank• Matrix effect• Detection limit
The “Scales” of Analytical Chemistry
Review Significant Figures
• What are sig figs?
• Rules:Addition/subtractionMultiplication/divisionLog/antilogExact numbers
• When to round?
Significant Figures Examples
• Add the numbers 1.0556, 7.113*10-2, and 0.81
• How many kilometers is 9.3 miles? (Use the conversion factor 1 km = 0.62137 mi.)
• A student measures the mass and volume of a liquid to determine its density. The volume is 25.00 mL. An empty beaker has a mass of 74.881 g, and the beaker with liquid is 99.437 g. What is the density?
• What is the pH of a 1.56*10-3 M hydrochloric acid solution?
Accuracy
• What is accuracy?
• Quantifying accuracy
• Assessing accuracy
• No true value?
Precision
• What is precision?
• Quantifying precision
• Assessing precision
Characterizing Data Example
Calculate the average, mode, standard deviation, relative standard deviation, and percent relative error for the following data set (density of pennies, post 1982 = 7.18 g/mL). (By hand first, then use your calculator’s stat mode…)
1. 7.22 g/ml2. 6.87 g/ml3. 7.03 g/ml4. 7.30 g/ml
Two Types of Error
1. Determinate error
– Sampling
– Method
– Measurement
– Personal
**can be constant or proportional**
Class A Tolerances
Two Types of Error
2. Indeterminate/random
Visualizing these:Determinate Indeterminate
Uncertainty
• What is uncertainty?
• DUI example
If you don’t learn anything else in this class…