Analysis carbonate

Experiment 3: Analysis of a Mixture of Carbonate and Bicarbonate
Conducted September 19-21, 2011

Purpose: To introduce the technique of titration. This is a very common wet chemical technique, and the determination of a wide variety of analytes can be determined by using this technique. This lab will also introduce the concept of use of standards. A number of secondary standards will beused, all of which are determined from a primary standard. The amount of the two different carbonate species via an indirect titration method will be determined.

Method: An unknown mixture of carbonate and bicarbonate was obtained and placed in a dessicator. Next, NaOH(s) was placed in a 500mL bottle with 500mL of water to make an approximately 0.1M solution. Concentrated HCl was thenplaced in a 1L bottle with 1L of water to make an approximate 0.1M solution of HCl. Approximately 0.51g of KHP was weighed for three different samples. This is used to standardize the base, which is used to standardize the acid. 2.0-2.5g of unknown was placed in a 250mL volumetric flask. This was then diluted to the mark with freshly boiled and cooled triply distilled water. 25mL of aliquot wastransferred to a 250mL Erlenmeyer via pipet. This was then titrated with standardized HCl using bromcresol green to determine the endpoint. This was repeated until tree good trials were obtained. 25.00mL of unknown and 50.00mL standard NaOH were then placed in a 250mL Erlenmeyer flask via pipet. 10mL of 10wt% BaCl2 was then placed in the Erlenmeyer flask and the flask was swirled to precipitateall the BaCO3. This was then titrated immediately with standard HCl using phenolphthalein indicator. This was repeated until three good trials were obtained. Relative percent carbonate and bicarbonate, and standard deviation was then calculated.

Reactions:
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Data:

Standardization of NaOH
Using 2.0255g NaOH in 500mL water
|Trial |Mass KHP (g)|Volume NaOH (mL) |Molarity NaOH (M) |
|1 |0.5106 |27.20 |0.0919 |
|2 |0.5102 |27.49 |0.0909 |
|3 |0.5100|28.21 |0.0885 |
|4 |0.5106 |27.02 |0.0925 |
|Average | | |0.091 |
|Standard Deviation|| |0.00176 |

Standardization of HCl
Using 8.33mL HCl in 1L water
|Trial |Volume NaOH (mL) |Molarity HCl (M) |
|1 |22.85 |0.0832 |
|2 |22.71|0.0833 |
|3 |22.88 |0.0832 |
|4 |22.71 |0.0833 |
|Average | |0.0833 |
|Standard Deviation||0.0000816 |

Total Alkalinity Titration
Using 2.1624g unknown in 250mL of CO2 – free water
Titrated using bromcresol green indicator
|Trial |Volume unknown (mL) |Volume HCl added (mL) |Molarity HCO3- (M) |Molarity CO32- (M) |
|1 |25.00 |33.10 |0.1103...