Quantitative Analysis Exam 1

Quantitative Analysis

determines how much of a specific substance is present

Qualitative Analysis

identifies what chemical species are present in a sample

Steps of Chemical Analysis

1. Formulate a question from a general problem

2. Select analytical procedure based on accuracy, sample size, and cost

3. Sampling a representative bulk material to analyze

4. Sample preparation by converting the bulk sample into a suitable form for measurement

5. Analysis by measuring the concentration of the analyze in replicate samples

6. Reporting and Interpretation by performing statistical calculation and drawing conclusions

Molarity

moles of solute/liters of solution

Molality

moles of solute/kilograms of solvent

Formal Concentration

total number of formula weights per liter of solution

Percent Composition

mass of solute/mass of solution * 100

Parts Per Million

mass of solute/mass of solution * 10⁶

Dilution

buoyancy correction

Volumetric Glassware

always read the bottom of the liquid meniscus at eye level

Calibrated Class A glassware

accounts for precise temperature and delivery standards

Systematic error

repeatable, traceable, and skews results consistently in one direction; can be eliminated via uncalibrated balance, bad standard

Random Error

unavoidable, unpredictable fluctuations above and below the true mean; cannot be eliminated

addition and subtraction sig figs

answer matches the fewest number of decimals places

Gaussian distribution

bell shaped curve centered at the population mean with width governed by standard deviation

mean

average of a sample set

standard deviation

measure of precision

coefficient of variation

standard deviation/mean *100

f test

compares the precision of two methods or sets of data

t test

compares two mean values to see if they differ significantly a a chosen confidence level

g test

identifies statistical outliers

confidence interval

range within which the true mean is expected to lie within given probability

method of least squares

draws the best-fit straight line through data points by minimizing the sum of the vertical deviations squared

Linear range

concentration interval over which instrument response is directly proportional to concentration

dynamic range

range from the limit of quantitation to where response bends away from linearity

standard deviation

• xi​ = individual measurement

• xˉ = sample mean (average)

• n = total number of measurements

• n−1 = degrees of freedom