Gravimetric Analysis

Quantitative Analysis Process of determining how much of one or more constituents are present in a sample Two Types of Quantitative Analysis: 1) Gravimetric Analysis – Uses weights 2) Volumetric Analysis – Uses volumes

Gravimetric Analysis Dissolves the sample Precipitates out one of the constituents Collects and weighs the precipitate Determines the weight of the constituent Calculates the percent of the constituent in the original sample

Example A unknown chloride salt of mass g is dissolved in water. Silver nitrate is added and g of AgCl precipitate is formed. What is the percent of chlorine in the original sample?

Statistics Used to analyze results Experiments are repeated several times It is important that the results are repeatable and not just random (there is precision)

Mean Average of the measurements mean = sum of results number of results

Deviation How much a result is different from the mean d = result - mean

Standard Deviation Gives an indication of the precision of the measurement s.d. = sum of the squares of deviations number of results - 1

Example An experiments results are 1, 3, and 5. Calculate the mean, the deviations from the mean, and the standard deviation.

What does it tell you? Any result more than two standard deviations from the mean is meaningless and should be discarded