Carbonate bicarbonate lab PDF

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Analysis of a Mixture of Carbonate and Bicarbonate 1

Chemistry 371 Analytical Chemistry Fall 2019 Analysis of a Mixture of Carbonate and Bicarbonate

Analysis of a Mixture of Carbonate and Bicarbonate 2

Abstract In this experiment titration techniques were used to determine the composition of a Carbonate bicarbonate mixture. After using direct and indirect titration of the sample 1010, the resulting mass percentages for the unknown were an average of 43. 6% of bicarbonate and an average of 7.44% of carbonate. My standard deviation ended up being a little high, so these results are not ideal. The main area of probable error would most likely be during the standardization of the HCl. This process was not as strait forward as the standardization of the NaOH. The process of boiling in the middle of the titration and problems with identifying the color change had large to do with this.

Introduction The purpose of the Analysis of a Mixture of Carbonate and Bicarbonate lab was to find the total alkalinity of an unknown mixture. We first use a strong standard acid to titrate with and to figure out the bicarbonate concentration by precipitating with barium which will mask the carbonate so you can then use back titrating to measure excess left over. This is a very important process and is used in many applications due to the fact that Carbonate and Bicarbonates can have a major effect on pH levels.(2) This experiment shows the advantages of direct and indirect methods using one sample with two indicators. (1)

Procedure Standardize HCl solution and NaOH solution were prepared use KHP dissolved in water to standardize the NaOH and then using the Na2CO3 to standardize the HCl. A mass of unknown was diluted in 250mL of double distilled, boiled water that was cooled to room temperature. 25mL of unknown was titrated using standardized HCl and bromocresol green as an indicator. 25mL of unknown, 50mL of NaOH, and 10mL of 36wt% BaCl2 was then mixed and a precipitate was formed of all the BaCO 3. This solution was then titrated using standardized HCl and phenolphthalein as an indicator. This was repeated for 3 trials.

Results and Data Data: Trial Number 1 2 3

Trial 1 2 3

Mass of KHP (g) 1.3470 1.3085 1.3467

Standardized Base Volume NaOH Used Molarity NaOH (M) (mL) 98.825 0.0668 93.90 0.0682 97.20 0.0678

Trial 1 2 3

Mass of Unknown (g) 2.4282 n/a n/a Standardized Acid Volume HCl used Molarity HCl (M) (mL) 32.45 0.0862 32.6 0.0859 33.75 0.0896

Analysis of a Mixture of Carbonate and Bicarbonate 3 Avg.

0.0676

Trial 1 2 3 Avg.

Avg.

Unknown Only (25mL) Volume HCl Used (mL) 23.35 23.825 23.625

Calculated Data Trial Mol CO3&HCO3 1 0.002036 2 0.002078 3 0.002060 Avg Std Dev

Mol NaOHtotal 0.00338 0.00338 0.00338

Mol NaOHw/HCl 0.002145 0.002211 0.002097

Calculations: Volume used to titrate:

Unknown, NaOH, and BaCl2 Trial Volume HCl Used (mL) 1 24.60 2 25.35 3 24.05 Avg.

Mol NaOHw/HCO3 0.001735 0.001669 0.001783

Mol CO3 0.000301 0.000409 0.000277

Mass% HCO3 43.60 41.94 44.80 43.45 1.4362

Mass% CO3 7.44 10.12 6.85 8.14 1.7428

Example for trial 1:

∆ V =V final−V initial

98.825 mL NaOH=99.325 mL−0.50 mL

Molarity of NaOH:

(

0.0872

Molarity of NaOH for trial 1:

)

( (

m KHP∗1mol KHP g∗1 mol KHP ∗1 mol NaO ∗1 mol NaOH 204.22 g KHP 204.22 g KHP 0.0668 M = 1 .3470 M NaOH = ÷∆ 1 mol KHP 1mol KHP Molarity of HCl:

(

m Na 2 co 3∗1 mol Na 2 CO 3 ∗1 mol HCL 105.988 g Na2 CO 3 M HCl = 1 mol Na2 CO 3 Moles of Carbonate and Bicarbonate:

´ HCl∗V HCl added =moles HCl M moles acid=moles base

Molarity of HCl for trial 1:

Moles of Carbonate and Bicarbonate for trial 1:

0.0872 M ∗0. 0 2335 L=0.002036 moles HCl ¿ 0.002036 moles carb ./bicarb .

Total moles of NaOH:

Total moles of NaOH for trial 1:

Moles of NaOH reacted with HCl:

Moles of NaOH reacted with HCl for trial 1:

´ NaOH ∗V NaOH ∈sample =moles NaOH M ´ HCl∗V HCl added =moles HCl M moles acid=moles base

Moles NaOH reacted with Bicarbonate:

)

g∗1 mol ∗1mol HCL 105.988 g ÷. 0.0862 M = 0.1504 1mol Na 2CO 3

0.0676 M∗0.0500 L=0.00338 moles NaOH 0.0872 M ∗0.02460 L=0.002145 moles HCl ¿ 0.002145 moles NaOH wit h HCl Moles NaOH reacted with Bicarbonate for trial 1:

moles NaOH wit h HCO3 =moles NaOH total−moles NaOH w mol w/ HCO 3=0.00338 moltotal −0.002145 molw / HC ¿ 0.001735 moles NaOH wit h HCO3 Moles of Bicarbonate:

moles HCO 3=moles NaOH Moles of Carbonate:

moles CO3= molesCO 3∧HCO 3−moles HCO 3 Mass percent of Bicarbonate:

Moles of Bicarbonate for trial 1:

¿ 0.001735 moles NaOH Moles of Carbonate for trial 1:

molCO 3=0.002036 mol CO 3∧ HCO 3−0.001735 mo ¿ 0.000301 molesCO 3 Mass percent of Bicarbonate for trial 1:

Analysis of a Mixture of Carbonate and Bicarbonate 4 moles HCO 3∗61.016 g HC O 3 =m HC O 3 1 mol HC O3 m HC O 3 ∗100 % =mass % m sample/10 Mass percent of Carbonate:

molesCO 3∗60.008 g C O 3 =m C O 3 1mol C O 3 m C O3 ∗100 %=mass % m sample

0.001735 mol HCO 3∗61.016 g HC O3 =0.105863 1mol HC O 3 0.105863 g HC O 3 ∗100 %= 43.60 % 2.4282 g /10 Mass percent of Carbonate for trial 1:

0.000301mol CO3∗60.008 g C O 3 =0.018062 gC 1 mol C O 3 0.018062 g C O 3 ∗100 %=7.44 % 2.4282 g /10

Discussion and Conclusions A primary standard is a substance that is pure and can be used immediately with calculated amounts. The primary standard can then be used to standardize a secondary standard. These secondary standards can then be calculated accurately with standardization. An indirect titration is also called a back titration. It involves determining the concentration of mixture through reacting it with a known number of moles of excess reagent. Excess is titrated with a second reagent and concentration of analyte is related to the amount of reagent consumed.

References and notes (1) Ind. Eng. Chem.1924167709-710 Publication Date:July 1, 1924 https://doi.org/10.1021/ie50175a019 (2) W. Sumerford. Determining an Alkali Carbonate in Presence of an Alkali Bicarbonate - A Colorimetric Method. Industrial & Engineering Chemistry Analytical Edition 1943, 15 (1) , 38-39. DOI: 10.1021/i560113a019....