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Chapter 5: QCE (page 113)
In Figure 5-6, the x-intercept is and its standard uncertainty is. Find theandconfidence intervals for the intercept.
Theandconfidence interval for the intercept has to be calculated asand.
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Here is a use objective for a chemical analysis to be performed at a drinking water purification plant: "Data and results collected quarterly shall will be used to determine whether the concentrations of haloacetates in the treated water demonstrate compliance with the levels set by the Stage 1 Disinfection By-products Rule using Method (a specification that sets precision, accuracy, and other requirements).
Which one of the following questions best summarizes the meaning of the use objective?
(i) Are haloacetate concentrations known within specified precision and accuracy?
(ii) Are thehaloacetates detectable in the water?
(iii) Dothehaloacetate concentrations exceed the regulatory limit?
Europium is a lanthanide element found at parts per billion levels in natural waters. It can be measured from the intensity of orange light emitted when a solution is illuminated with ultraviolet radiation. Certain organic compounds that bindEu(III)are required to enhance the emission. The figure shows standard addition experiments in which10.00mLof sample and20.00mLcontaining a large excess of organic additive were placed in 50-mL volumetric flasks. Then Eu(III) standards (0,5.00,10.00,or15.00mL) were added and the flasks were diluted to50.0mLwithH2O. Standards added to tap water contained0.152ng/mL(ppb) of Eu(III), but those added to pond water were 100 times more concentrated (15.2 ng/mL).
(a) Calculate the concentration of Eu(III)(ng/mL) in pond water and tap water.
(b) For tap water, emission peak area increases by.4.61units when 10.00mL of 0.152ng/mL standard are added. This response is4.61 units/1.52ng = 3.03units per ng ofEu(III). For pond water, the response is12.5units when10.00mLof15.2ng/mLstandard are added, or0.0822units per ng. How would you explain these observations? Why was standard addition necessary for this analysis?
Chloroform is an internal standard in the determination of the pesticide DDT in a polarographic analysis in which each compound is reduced at an electrode surface. A mixture containing chloroform andDDT gave signals offor chloroform andfor DDT. An unknown solutioncontaining DDT was placed in avolumetric flask andof chloroform (FM 119.39, densitywere added. After dilution to the mark with solvent, polarographic signals of andwere observed for the chloroform and DDT, respectively. Find the concentration of DDT in the unknown.
1.00 mL of blood serum was diluted to 25.00 mL in each flask of a standard addition experiment like Figure 5-7 to measure a hormone with a molecular mass of 373 g/mol. The x-intercept of the graph was 4.2 ppb (parts per billion). Find the concentration of hormone in the serum and express your answer in ppb and molarity. Assume that the density of serum and all solutions is close to 1.00 g/mL
What is the difference between a false positive and a false negative?
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