Analytical Chemistry, data anylisis.docx

Analytical chemistry

1. LECTURE 9: STATISTICAL TREATMENT OF
ANALYTICAL DATA

2. Probability Distributions of Populations

3. The most commonly encountered continuous distribution
is the Gaussian, or normal distribution.
The frequency of occurrence for a value, X, is
given by

4. ce,σ
The shape of a normal distribution is determined by two
parameters, the first of which is the population’s central,
or true mean value, μ, given as
The second parameter is the population’s varian
2

5. Normal distributions
for
(a) μ = 0 and σ
2
= 25;
(b) μ = 0 and ??????
2
= 100;
(c) μ = 0 and σ
2
= 400.

6. onandσ
Note Each normal distribution contains a single maximum
corresponding to μ and that the distribution is symmetrical about
this value.
increasing the population’s variance increases the
distribution’s spread while decreasing its height.
Because the normal distribution depends solely μ
2
, the
area, or probability of occurrence between any two limits defined
in terms of these parameters is the same for all normal distribution
curves

8. andσ
The amount of aspirin in the analgesic tablets from a particular
manufacturer is known to follow a normal distribution, with
μ = 250 mg
2
= 25.
In a random sampling of tablets from the production line, what
percentage are expected to contain between 243 and 262 mg of
aspirin?

12. NEXT LECTURE