Ion Exchange Lab
Determination of Percent Potassium
& Percent Iron in an Iron Oxalate Salt by Ion Exchange
Introduction: This experiment involves determining both the percent potassium (K) and iron (Fe) in a single titration after passing a solution containing a known mass of complex salt through an ion exchange column.
Ion Exchange: Certain materials called ion exchange resins consist of rather large molecules which contain ions that can be displaced.
The resins are solids, insoluble in water, usually granular in texture, which when added to water swell to form a slurry. The ionizable group on the resin ionizes in the presence of water, a process represented by Equation 1 for a resin containing a sulfonic acid group. (-SO3-H).
R-SO3-H + H2O R-SO31- , H3O+ (1)
R represents the large insoluble resin molecule to which a sulfonic acid group is chemically bonded, H3O+ represents acid hydronium ion bound to the resin sulfonate ion. This particular type of resin is called a cation exchange resin for reasons described later, and the chemical form of the resin represented in Equation 1 is called the acid form for obvious reasons.
When a slurry of the resin in water is poured into a vertical glass or plastic column equipped with a porous plug at the bottom to trap the resin and excess water is allow to flow out, the column becomes filled with water soaked resin, as shown in Figure 1.
resin
porous plug
Figure 1
If an aqueous solution of a salt such as KCl (K+ + Cl-) is poured into the resin filled column, the KCl solution will displace the solution surrounding the resin and that solution will elute from the bottom of the column. In the process, as the KCl solution passes down the column, K+ ions displace (exchange with) H3O+ ions and aqueous HCl (H3O+ + Cl-) elutes from the column, Equation 2.
R-SO3-,H3O+ + K+ + Cl- R-S)3-,K+ + H3O+ + Cl- (2)
Thus the solution coming out of the column will contain a quantity
& Percent Iron in an Iron Oxalate Salt by Ion Exchange
Introduction: This experiment involves determining both the percent potassium (K) and iron (Fe) in a single titration after passing a solution containing a known mass of complex salt through an ion exchange column.
Ion Exchange: Certain materials called ion exchange resins consist of rather large molecules which contain ions that can be displaced.
The resins are solids, insoluble in water, usually granular in texture, which when added to water swell to form a slurry. The ionizable group on the resin ionizes in the presence of water, a process represented by Equation 1 for a resin containing a sulfonic acid group. (-SO3-H).
R-SO3-H + H2O R-SO31- , H3O+ (1)
R represents the large insoluble resin molecule to which a sulfonic acid group is chemically bonded, H3O+ represents acid hydronium ion bound to the resin sulfonate ion. This particular type of resin is called a cation exchange resin for reasons described later, and the chemical form of the resin represented in Equation 1 is called the acid form for obvious reasons.
When a slurry of the resin in water is poured into a vertical glass or plastic column equipped with a porous plug at the bottom to trap the resin and excess water is allow to flow out, the column becomes filled with water soaked resin, as shown in Figure 1.
resin
porous plug
Figure 1
If an aqueous solution of a salt such as KCl (K+ + Cl-) is poured into the resin filled column, the KCl solution will displace the solution surrounding the resin and that solution will elute from the bottom of the column. In the process, as the KCl solution passes down the column, K+ ions displace (exchange with) H3O+ ions and aqueous HCl (H3O+ + Cl-) elutes from the column, Equation 2.
R-SO3-,H3O+ + K+ + Cl- R-S)3-,K+ + H3O+ + Cl- (2)
Thus the solution coming out of the column will contain a quantity