More on “Signal”
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Interference
Method blank
Matrix effect
Detection limit
The “Scales” of Analytical Chemistry
Review Significant Figures
• What are sig figs?
• Rules:
Addition/subtraction
Multiplication/division
Log/antilog
Exact 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.
2.
3.
4.
7.22 g/ml
6.87 g/ml
7.03 g/ml
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…