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17 Nov 2019
How to answer the post lab question
Your unknown is an aqueous solution containing an amount of a magnesium salt and hydrochloric acid. Quantitatively transfer a 10.00 mL aliquot of the unknown solution to a 250 mL Erlenmeyer flask. Add 2-3 drops of methyl red. and titrate with your base. Express the results as the molarity of HCI in the unknown. This step is completed to determine the amount of titratable acid that may be present in your sample. You may repeal replicate titrations if you wish, though you must make sure you retain enough solution for the ion exchange portion of the experiment. Add 10.00 mL aliquot of your unknown solution to the top of the prepared column. Start collecting your aliquots in a clean Erlenmeyer flask. After the unknown has eluted nearly to the top of the resin bed, wash with about one bed volume of distilled water. Repeat the washing two more times, allowing each volume of wash to elute to the top of the resin bed before adding the next volume. All of the effluent should be collected. Add 3-4 drops of methyl red to the effluent and titrate with your 0.1 M NaOH. Do not discard the solution. After the endpoint is attained, place the titration flask under the column, and elute another one-half bed volume of distilled water into the solution you previously titrated. If the indicator changes to red (acidic solution), continue the titration with your standardized base to a yellow endpoint. Then repeat the process of eluting one-half bed volumes of distilled water and titrate if necessary, until the eluted distilled water does not require more than one drop of the base to change the indicator to yellow. Repeat the procedure above for a total of three unknown determinations. Recharge the column by converting the column to its fully protonated form (see instructions above) between each sample. Use the total amount of base used in this process to calculate, the millimoles of H^+ displaced from the resin, the millimoles of Mg^2+ remaining in the column on exchange sites, and finally the concentration of Mg^2+ in terms of mg of Mg^2+ per mL of sample. For your final answer, report the average concentration of Mg^2+ in your unknown sample in mg/mL and the confidence limits at the 95% level. Post lab question. Experiments 9 and 10 are different methods for the determination of alkali earth metals. Use your data, calculate and compare the %relative standard deviation for experiments 9 and 10. Discuss the difference (if any) and suggest reasons why the values are different, or if they are similar, suggest reasons why values are similar.
How to answer the post lab question
Your unknown is an aqueous solution containing an amount of a magnesium salt and hydrochloric acid. Quantitatively transfer a 10.00 mL aliquot of the unknown solution to a 250 mL Erlenmeyer flask. Add 2-3 drops of methyl red. and titrate with your base. Express the results as the molarity of HCI in the unknown. This step is completed to determine the amount of titratable acid that may be present in your sample. You may repeal replicate titrations if you wish, though you must make sure you retain enough solution for the ion exchange portion of the experiment. Add 10.00 mL aliquot of your unknown solution to the top of the prepared column. Start collecting your aliquots in a clean Erlenmeyer flask. After the unknown has eluted nearly to the top of the resin bed, wash with about one bed volume of distilled water. Repeat the washing two more times, allowing each volume of wash to elute to the top of the resin bed before adding the next volume. All of the effluent should be collected. Add 3-4 drops of methyl red to the effluent and titrate with your 0.1 M NaOH. Do not discard the solution. After the endpoint is attained, place the titration flask under the column, and elute another one-half bed volume of distilled water into the solution you previously titrated. If the indicator changes to red (acidic solution), continue the titration with your standardized base to a yellow endpoint. Then repeat the process of eluting one-half bed volumes of distilled water and titrate if necessary, until the eluted distilled water does not require more than one drop of the base to change the indicator to yellow. Repeat the procedure above for a total of three unknown determinations. Recharge the column by converting the column to its fully protonated form (see instructions above) between each sample. Use the total amount of base used in this process to calculate, the millimoles of H^+ displaced from the resin, the millimoles of Mg^2+ remaining in the column on exchange sites, and finally the concentration of Mg^2+ in terms of mg of Mg^2+ per mL of sample. For your final answer, report the average concentration of Mg^2+ in your unknown sample in mg/mL and the confidence limits at the 95% level. Post lab question. Experiments 9 and 10 are different methods for the determination of alkali earth metals. Use your data, calculate and compare the %relative standard deviation for experiments 9 and 10. Discuss the difference (if any) and suggest reasons why the values are different, or if they are similar, suggest reasons why values are similar.