Quant Lab 4

Quant Lab 4 - Cation Exchange By: Cassandra Shenefelt TA:...

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Cation Exchange By: Cassandra Shenefelt TA: Hilary Easter Designator: Dr. MacCarthy Thursday 2:00 PM to 4:50 PM February 21, 2008 Abstract The goal of this experiment was to find the molarity of an unknown solution using the ion-exchanging capability of resin. This involved titrating ion rich solutions through the resin and flushing de-ionized (DI) water through to help get all the H + ions. This was then titrated with the standardized NaOH solution to find the molarity of the unknown solution. Background Resin is a porous solid in which a long carbon polymer and acid groups interact with surrounding solutions. This causes H + ions to be formed and titrated out, this than assists in finding the amount and molarity of the unknown substance placed through the resin using a simple equation: 2Resin-SO 3 -H + M +2 Resin-(-SO 3 ) 2 -M + 2H + Introduction The ion exchanging capability of a substance can help determine the mass of an unknown substance. In the case of this lab, resin is the ion-exchanger and the unknown is a Ca solution. Generating the resin with an acid wash helped to create the groups which had an ion attached to it. In the first part of the lab, a known Ca solution was used to familiarize ones self with the capability and process of the column, in the second part an unknown amount of Ca was used. Methods For this experiment it had two parts, the first was preparing the ion- exchange in the column and getting familiarized with the steps taken to obtain the correct amount of H + ions and titrate that amount correctly with the standardized NaOH solution. The second part was analyzing an unknown substance using the methods in the previous steps to determine the molarity and weight percentage of the unknown. The first part required several steps. Each one must be followed exactly to correctly prepare and use the ion exchange column. The first step was to obtain 25mL of ion- exchange resin (Dowex 50W-X8, 20-50 mesh) in a 150mL beaker. This required precision, to obtain the resin one must get as much resin and as little liquid out of the container as possible but still keep the resin hydrated, the level of the resin should be the solid substance at the 25mL mark, not the liquid. Also, in the first step, obtain a second beaker of about 100mL of 2M HCl. Next, mix half the HCl with the resin and thoroughly stir for approximately three minutes. Once the resin has settled, keeping the resin moisturized, drain the clear liquid, keeping all the resin, into a clearly marked 600mL waste beaker. Repeat
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this HCl wash of the resin to fully ensure all the H + ions have attached themselves to the groups on the resin. Thirdly, to wash off the excess H + ions mix about 50mL of de-ionized water with the resin, stir this, let it settle and drain the clear solution into the waste beaker. Repeat this wash until the pH paper shows that it is more acidic than the de-ionized water used. To create the ion-exchange
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Quant Lab 4 - Cation Exchange By: Cassandra Shenefelt TA:...

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