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Chapter 26: Q7P (page 746)
What is deionized water? What kind of impurities are not removed by deionization?
Deionized water:Water that has passed through ion-exchangers to convert the present cations to protons and present anions to hydroxides
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Material balance. If you intend to measure all the anions and cations in an unknown, one sanity check on your results is that the total positive charge should equal the total negative charge. The table lists concentrations of anions and cations measured in pond water in an undergraduate experiment and expressed in mg/mL.
Find the total concentration of negative and positive charge (mol/L) to assess the quality of the analysis. What do you conclude about this analysis?
Figure 26-24 shows the effect on resolution of increasing voltage from 28 to120kV
(a) What is the expected ratio of migration timesin the two experiments? Measure the migration times for peak 1 and find the observed ratio.
(b) What is the expected ratio of plates in the two experiments?
(c) What is the expected ratio of bandwidths?
(d) What is the physical reason why increasing voltage decreases bandwidth and increases resolution?
The following substances were separated on a gel filtration column. Estimate the molecular mass of the unknown.
Totarlsulfexperimevt: Inorganic cations can be quantified by passing a salt solution throagh a cation-exchange columan in the form and titruting the relcasod H+with strong base. The moles of titrant equal the equivalenss of catioa charge in solution.
(a) What volume of 0.0231 M NaOH is needed to titrate the eluate when 10.00ml of ,have been loaded on a cation exchange columan in the H+foem?
(b) A 0.2692g sample of unknown salt is dissolved in demonized waler and loasedoato a cation exchange column in the H+form. The columin is rinsed with deionined water and the combincd loading and rinse solutions are titrated with 0.1396M KOH. A volume of 30.64mL is required to reach the endpoint. How many equivalents of cation are in the sample? Find the millieguivalents of cation per gram of sample (meq/g).
(c) The mass of substance containing one cquivalent is called the equivalent mas. If the cation has a +1 charge, the equivalent mass equals the molar mass. If the cation has a +2 charge, the equivalent mass is half the molar mass. What is the equivalent mass of the sample in (b)?
Blue Dextran 2000 was eluted during gel filtration in a volume of 36.4mL from a 40 * 2cm (length diameter) column of Sephadex G-50, which fractionates molecules in the molecular mass range 1500-30000.
(a) At what retention volume would hemoglobin (molecular mass 64000 ) be expected?
(b) Suppose that radioactive, which is not adsorbed on the column, is eluted in a volume of 109.8 mL. What would be the retention volume of a molecule with Kav= 0.65?
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