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…