Download presentation
Presentation is loading. Please wait.
1
CHE 315 – Lecture 5 9/9/05 Statistics
2
Quiz 2 1.An iron ore was analyzed by dissolving a 1.1324-g sample in concentrated HCl. After precipitation, filtration and washing, the residue was ignited to give 0.593 g of pure Fe 2 O 3 (159.69 g/mol). What was the % Fe (55.847 g/mol) in the iron ore? 2.Stormwater running off of parking lots have typical copper (63.55 g/mol) concentrations of 100 ppb. Convert that concentration to molarity.
3
Arithmetic mean (average) Best way to express results if data is symmetrical
4
Standard Deviation Measures how closely the data is clustered around the mean Degrees of freedom: n-1
5
Variance = s 2 Relative standard deviation –(coefficient of variance)
7
Gaussian distribution Approximate µ by and σ by s
9
z Used to express deviations from the mean in multiples of the standard deviation
12
Probabilities Range Percentage of measurements µ + 1 σ 68.3 µ + 2 σ 95.5 µ + 1.96 σ 95 µ + 3 σ 99.7
13
Confidence interval Range of values that will contain the true mean of the population to a given probability C.I. when s is large? small? C.I. when n is large? small?
16
Advantages to larger sample size –More confident of true value Disadvantages of larger sample size –Money –Time –Not enough sample
17
z vs. t t tends to z at large n’s Values of both in tables depend on confidence level –t also depends on degrees of freedom → t for a single measurement → t for n measurements
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.