Chemistry 160
Questions for Laboratory 3
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1. A student obtained the following results for weight % sulfate in a gravimetric determination

25.279 25.304 25.292 25.410
25.287 25.313 25.300 25.275
  1. Apply the Q-test to the discordant value (2.410). Should it be rejected? (Show your work)
  2. Calculate the mean, variance, standard deviation, and relative standard deviation. (Show your work)
  3. Report the mean at the 95% confidence level.

 

 

 

 

 

 

 

 

 

 

2. Compare the confidence limits calculated in steps 1, 3, and 5 of the experiment. What are the reasons for the differences? Compare step 1 to step 3, step 1 to step 5, and step 3 to step 5.

 

 

 

 

 

 

 

3. An analysis laboratory suspected of poor work was given a National Institute of Standards and Technology (NIST) standard alloy containing 35.6743% Cu. Analysis of 5 aliquots of this alloy gave the following %Cu values:

35.80 % 35.89 % 36.12 % 36.03 % 36.20 %

Use to the Student's-t formula to determine the "true" mean with confidence level of 95%. Are the laboratories results statistically different from the NIST standard value at the 95% level?

 

 

 

 

 

 

 

 

4. Is there a significant difference between the weight of water determined in Step 4 and the mean weight determined in Step 1? What type of error is (would be) responsible for the difference?