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Chapter 26: Q27P (page 748)
What is electroosmosis?
Electroosmosis (electroendosmosis) is the pumping process in which charged particles tend to migrate to a less charged area.
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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)?
The water-soluble vitamins niacinamide (a neutral com- pound), riboflavin (a neutral compound), niacin (an anion), and thiamine (a cation) were separated by micellar electrokinetic chromatography in 15mMborate buffer (pH8.0)with 50mMsodium dodecyl sulphate. The migration times were niacinamide (8.1min), riboflavin (13.0min), niacin (14.3min), and thiamine. What would the order have been in the absence of sodium dodecyl sulphate? Which compound is most soluble in the micelles?
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?
Would molecular exclusion, affinity, or hydrophobic interaction chromatography be most appropriate for each of the following applications?
(a) State the purpose of the separator and suppressor in suppressed ion chromatography. For cation chromatography, why is the suppressor an anion-exchange membrane?
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